The crystal structure of the new mineral (IMA 2020-073) devilliersite Ca₄Ca₂Fe³⁺₁₀O₄[(Fe³⁺₁₀Si₂)O₃₆], crystalizing in space group P–1 with cell parameters a = 10.56619(10) Å, b = 10.94969(11) Å, c = 9.08459(7) Å, α = 106.4300(8)°, β = 95.7466(7)°, γ = 124.2978(11)°, V = 786.906(16) ų, Z=1, was solved from single-crystal diffraction data, collected at PSI(SLS). Devilliersite, as well as khesinite, Ca₄Mg₂Fe³⁺₁₀O₄ [(Fe³⁺₁₀Si₂)O₃₆] [1], is a ^VIFe³⁺-analog of dorrite, Ca₄Mg₂Fe³⁺₁₀O₄[(Al₁₀Si₂)O₃₆] [2] and synthetic SFCA (Silico-Ferrite of Calcium and Aluminium) [3]. The structural formula of minerals of the dorrite–khesinite series can be written as ^VII(A1₂A2₂)_Σ4 ^VI(M1M2M3₂M4₂M5₂M6₂M7₂)_Σ12O₄[(T1₂T2₂T3₂T4₂T5₂T6₂)_Σ12O₃₆], where A are seven coordinated sites, M are octahedral sites and T are tetrahedral sites (Figure 1). The total scattering densities at the cation positions were determined using the atomic scattering factors combined with a refinement of the individual site occupancies and results of microprobe analysis.

In the structure of devilliersite all of the A-sites are fully occupied by calcium. However, chemical analyses show that additional 0.68 Ca atoms are present. For crystallochemical reasons this excess Ca has to be expected at the largest octahedral site M5, where it was placed and fixed for the refinement. The remaining scattering power at the M5 site is explained by Mg. The octahedral M1, M2, M3, M4 and M6 sites are dominated by Fe³⁺, their scattering power was modelled with Fe and Mg, and converged for all sites to ~93% Fe. The M7 octahedra shows the smallest level of distortion, with bond lengths ranging from 1.999(2) to 2.75(19). In the Ti-rich minerals of the rhönite-group, titanium is found at the M7 site. Therefore, we fixed Ti at this site, according to the results of the chemical analysis, and the remaining occupancy was refined as Fe vs. Mg. Scattering power indicates that the T4 site in devilliersite is fully occupied by Si. Occupancy of all other tetrahedral sites was refined as Al vs Fe. The refined chemical formula is ^VIICa₄^VI(Ca_1.36Mg_1.33Fe_9.07Ti_0.24)_Σ12O₄^IV(Al_3.24Fe_6.76Si₂)_Σ12O₃₆.

[1] Galuskina, I.O., Galuskin, E.V., Pakhomova, A.S., Widmer, R., Armbruster, T., Krüger, B., Grew, E.S., Vapnik, Ye., Dzierazanowski, P., Murashko, M (2017). Eur. J. Mineral, 29, 101–116

[2] Cosca, M.A., Rouse, R.R. and Essene, E.J. (1988). Am. Miner, 73, 1440-1448.

[3] Kahlenberg, V., Krüger, H., Goettgens, V.S. (2019). Acta Crystallogr. B75, 1126-1136.

Funding: European Union's Horizon 2020 research and innovation program, project CALIPSOplus, grant No. 730872.

Abstract:

Refractory materials from kaolinitic clays and clay chamotte or quartz were studied to increase the refractoriness under load at temperature above 1300°C. Two different clays mined in Burkina Faso were used and chamotte grains were obtained by preliminary firing a local clay. Fired materials at 1350-1400°C present a typical granular composite microstructure were large grains of chamotte or quartz are embedded in the clay matrix phase. Under load at high temperature, the behavior of material is influenced by the nature of the clay matrix phase that progressively melt at high temperature, the type of chamotte or quartz grains, the grain sizes of different phases and the sequence of the thermal transformations during firing. Kinetics of creep under a constant load were characterized against temperature and time. It gives the typical temperatures at fixed creep strains, that’s a well-recognized method for the refractoriness quantification. It’s shown that the kinetic of creep change with the variation of viscosity with temperature of the melted clay matrix phase, that’s related to both the chemical composition and the extend of the micro-composite nature of the heat transformed clays. Results also indicated that values of activation energy for creep are correlated to the refractoriness of materials.

La ilmenita es uno de los minerales más comunes en la corteza terrestre, a menudo se encuentra en rocas ígneas y arenas negras de depósitos aluviales y puede ubicarse en diferentes partes del mundo; se utiliza como fuente natural de TiO2 y Fe y como catalizador en procesos de fotodegradación [1]. Una investigación realizada en el Grupo de Investigación en Química Estructural - GIQUE y Grupo de Investigaciones en Minerales, Biohidrometalurgía y Ambiente - GIMBA utilizando negro rico en ilmenita de Barbacoas (Nariño, Colombia) para aplicaciones fotocatalíticas encontró que la superficie específica del mineral (2.4- 4,2 m2 / g) es bastante bajo en comparación con el de los fotocatalizadores comunes (20-50 m2 / g) [2,3]. Con el objetivo de inducir cambios morfológicos que conduzcan a un aumento de la superficie, eso implicaría más sitios activos disponibles para la reacción; Esta investigación propone someter concentrados ricos en ilmenita a molienda de bolas de alta energía asistida por soluciones ácidas de ácido acético y ácido sulfúrico, ya que los ácidos pueden provocar cambios en la distribución y estado de oxidación de los elementos en la superficie mineral, produciendo poros y grietas en la superficie del mineral. superficie [4,5]. Sin embargo, la molienda de alta energía en presencia de soluciones ácidas puede modificar significativamente la cristalografía de materiales nanoestructurados, por lo tanto, es importante evaluar el efecto de la tensión aplicada sobre el tamaño de partícula, área superficial y composición, mientras se trazan cambios en la microestructura de ilmenita. El producto del tratamiento con ácido se obtuvo evaluando la concentración de ácido en la solución 1, 3 y 5% p / v, tiempo (1-3 h), velocidad de molienda 650 rpm, relación peso bola / potencia BPR (3: 1 , 10: 1 y 20:

Particle size distribution was measured by dynamic light scattering (DLS) and the minimum average particle size of 325 nm was reached by milling for 1 h with BPR 20:1 and size of grinding medium of 4.0 mm. Qualitative analysis of the XRD pattern of the samples performed using the software Diffrac.EVA showed the presence of ilmenite, hematite and rutile as crystalline phases (Fig. 1) and the quantitative phase analysis in the XRD patterns reported ilmenite as the phase in greater proportion using Diffrac.TOPAS. although no changes were observed in the position of the peaks in the powder XRD patterns of the samples milled with neither the acid solutions, decreasing in the intensity and widening of the peaks were noticed (Fig. 1), which evidenced amorphization of the phases as a result of the stress applied. The morphology evaluated by scanning electron microscopy (SEM) ratify the decrease in particle size and showed different shapes of particle for both acid solutions however, it was noted that acetic acid slightly favours the decrease in particle size (Fig. 2). In order to further improve the properties of the material it was decided to increase the concentration of the acid solutions and milling time.

There are several naturally occurring minerals that show temperature induced phase transitions, leading to a variety of materials which display specific properties such as superionic conductivityand ferroic behaviour.^[1-5] Some of the minerals crystallize with different hydration levels and show phase transitions at elevated temperature.^[2,3] It is important to note that superionic conductors exhibit high ionic conductivity ( ≈10^-3 to 10^-1 S/cm) at modest temperatures (400-600 °C) and are playing a major role to design next generation solid state batteries.^[1,4] The ionic conductivity of a material and its crystal structure are highly correlated with each other. In this context, the phase behaviour of compound belongs to the Vanthoffite family, Na₆Co(SO₄)₄.xH₂O (x = 2, 4) with temperature has been investigated. Single crystals of di-and tetra-hydrates of the mineral Na₆Co(SO₄)₄ grow concomitantly from aqueous solution containing stoichiometric molar ratio of starting materials. Both of this hydrated forms have similar morphology and crystallize in P`1 with Z=1. In fact, the elusive anhydrous crystal (Na₆Co(SO₄)₄) [inset Fig. 1a] could be produced in situ from the tetra-hydrate/di-hydrate crystal and the transition pathway has been characterized via variable temperature single crystal X-ray diffraction analysis. Further, we have also examined the phase transitions displayed by the anhydrous phase using in situ powder X-ray diffraction and in situ Raman spectroscopy with respect to temperature [Fig. 1b]. The structural features are shown to correlate with the conductivity measurements with the super ionic behaviour (σ =1.1× 10^-2 S/cm) appearing at 570 ˚C [Fig. 1a]. These observations are significant for the development and understanding of mineral based solid electrolytes.

[1] Sharma, V., Swain, D., Guru Row, T. N. (2017). Inorg. Chem. 56, 6048.

[2] Swain, D., Guru Row, T. N. (2009). Inorg. Chem. 48, 7048.

[3] Saha, D., Madras, G., Guru Row, T. N. (2011). Cryst.Growth Des. 11, 3213.

[4] Swain, D., Guru Row, T. N. (2007). Chem. Mater. 19, 347.

[5] Pradhan, G. K., Swain, D., Guru Row, T. N., Narayana, C. (2009). J. Phys. Chem. A 113, 1505.

The roméite-group [1,2] is part of the pyrochlore supergroup and comprises some cubic oxides of A_2-mB₂X_6-wY_1-n formula in which Sb⁵⁺ predominates in the B-site. Indices m, w and n indicate vacancies in A, X and Y crystallographic sites, respectively. A-site is typically occupied by cations with ionic radii greater than 1.0Å or H₂O, whereas X-site is usually occupied by O^2-, but smaller amounts of OH^- or F^- are also commonly found. Finally, Y-site is typically occupied by anions O^2-, OH^- or F^-; however, large ionic radii monovalent cations (>1.0Å) such as K⁺, Cs⁺ and Rb⁺, or even H₂O can occupy it. Since the predominance of Sb⁵⁺ for B site is already known, the correct A and Y main occupants determine different minerals in the group and are important for the discovery of new mineral species [3]. As a source of Sb, the roméite-group minerals are economically relevant, since Sb is present in different applications, from cosmetic industry to the metal alloy production. However, only five roméite-group mineral species, namely fluorcalcioroméite, hydroxycalcioroméite, hydroxyferroroméite, oxycalcioroméite, and oxyplumboroméite have been approved by IMA. Many others can probably be discovered from possible chemical substitutions at crystallographic sites. This study analysed three different samples and determined their chemical composition by electron microprobe analysis and Raman spectra and crystal structure obtained from single-crystal X-ray diffraction. The first sample occurs in Kalugeri Hill, Babuna Valley, Jakupica Mountains, Nezilovo,Veles, Macedonia, whereas the other two occur in Prabornaz Mine, Saint Marcel, Valle d'Aosta, Italy. Sample 1 was identified as fluorcalcioroméite, and samples 2 and 3 as hydroxycalcioroméite. These are the first descriptions of these mineral species at the mentioned occurrences.

All samples belong to the cubic crystal system, space group ??3̅?, Z = 8, where ? = 10.2881(13)Å, V = 1088.9(4)ų for sample 1, ? = 10.2970(13)Å, V = 1091.8(4) ų for sample 2, and ? = 10.289(6)Å, V = 1089.3(19)ų for sample 3. The crystal structure refinements led to the convergence of R-factors of the three samples: 1) R₁ = 0.016. wR₂ = 0.042 and Goodness-of-fit = 1.176; 2) R₁ = 0.230. wR₂ = 0.049 and Goodness-of-fit = 1.095; 3) R₁ = 0.029. wR₂ = 0.090 and Goodness-of-fit = 1.338. Bond-valence calculations validated the crystal structure refinements determining the correct valences at each crystallographic site. Discrepancies observed in the Sb⁵⁺ bond-valence calculations were solved with the use of the proper bond valence parameters revised by Mills et al. (2009) [4]. The resulting structural formulas were (Ca_1.29Na_0.55□_0.11Pb_0.05)_Σ=2.00(Sb_1.71Ti_0.29)_Σ=2.00(O_5.73OH_0.27)_Σ=6.00(F_0.77O_0.21OH_0.02)_Σ=1.00 for sample 1, (Ca_1.30Ce_0.51□_0.19)_Σ=2.00(Sb_1.08Ti_0.92)_Σ=2.00O_6.00(OH_0.61O_0.21F_0.18)_Σ=1.00 for sample 2, and (Ca_1.61□_0.24Na_0.15)_Σ=2.00(Sb_1.80Ti_0.20)_Σ=2.00O_6.00(OH_0.48F_0.35O_0.17)_Σ=1.00 for sample 3. The Raman spectra of all samples exhibited the characteristic bands of chemical bonds present in roméite-group minerals - the most evident one corresponded to the stretching of Sb-O bond around 510 cm^-1. Peaks around 1600 and 3600 cm^-1 were observed, confirming the presence of water in the structure.

[1] Atencio, D., Ciriotti, M., Andrade, M. (2013). Mineralogical Magazine. 77, pp. 467-473.

[2] Mills, S. J. (2017). European Journal of Mineralogy. 29, pp. 307-314.

[3] Atencio, D., et al. (2010). Canadian Mineralogist. 48, pp. 673-698.

[4] Mills, S. J., et al. (2009). Zeitschrift für Kristallographie. 229, pp. 423-431.

Oxidotellurates show a vast structural diversity, especially with tellurium in the +IV oxidation state, which has been summarized and categorized recently by Christy et al. ^[1]. This can be attributed to the 5s² electron lone pair of Te^IV. Its large space consumption often leads to rather low symmetric and one-sided coordination polyhedra and to the formation of modular structures like clusters, chains, layers or open-framework clusters penetrated by channels ^[2].

Single crystals of Cd₄Te^IV₅O₁₄, a newly discovered compound in the Cd/Te^IV/O-system, were obtained under hydrothermal conditions from a mixture of Cd(NO₃)₂∙4H₂O and K₂TeO₃ (molar ratio 4:5). The educts were mixed together in a teflon vessel, which was filled with water to about ⅔ of its volume and then heated inside a steel autoclave to 483 K for a week. The title compound appeared as a minor product besides CdTeO₃ ^[3]. Single crystals of Cd₄Te₅O₁₄ are colourless and bar-shaped.

The asymmetric unit of the monoclinic unit cell (C2/c, a = 11.9074(3), b = 14.3289(3), c = 8.7169(2) Å, β = 113.629(1) °, V = 1362.58(6) ų) contains three Te, three Cd and seven O sites. With the exception of one Te and two Cd sites that are located on the 4e position (site symmetry 2), all atoms are located on the general 8f Wyckoff position. The Cd sites are all coordinated by six oxygen atoms in a range of 2.235(2)-2.539(2) Å. By edge- and corner-sharing the [CdO₆]-polyhedra form an open three-dimensional framework. The Te^IV sites exhibit a coordination number of 4, which is better described as 3+1 for the Te1 and Te2 sites. The [TeO₄]-polyhedra have a bisphenoidal shape which is derived from a distorted [TeψO₄] trigonal bipyramid where the lone pair occupies an equatorial position.

The [TeO₄]-units are connected to each other by corner- and edge-sharing. This way they form helical [Te₅O₁₄]^{8 ̶} chains oriented parallel [203]. The sequence of the atomic sites ( ̶ Te3 ̶ Te2 ̶ Te1=Te1 ̶ Te2 ̶ ) repeats after 5 atoms which makes it a fünfer-chain. For Te-O-single-chain structures only zweier, dreier, vierer, sechser and achter-chains (repeating units of 2, 3, 4, 6 and 8 Te-atoms) have been found ^[1]. Using the nomenclature used by Christy et al. ^[1] the chains are denoted as (… ̶ ◊ ̶ ◊ ̶ ◊=◊ ̶ ◊ ̶ …). Considering the translational symmetry of the chain, a periodicity of 10 Te-atoms is found until the helix repeats itself (Fig. 1). Moving 10 Te-atoms up the chain corresponds to a translation of 2a+3c.

--- Figure 1 ---

Figure 1. [Te₅O₁₄]-chains in Cd₄Te₅O₁₄; symmetry codes: i) ½-x, -½+y, ½-z; ii) ½-x, ½-y, 1-z; iii) ½+x, -½+y, 1+z; iv) 1-x, y, 1½-z; v) 1+x, -y, 1½+z

The only other known structures with the composition M₄Te₅O₁₄ are two polymorphs of Ca₄Te₅O₁₄ ^[4-5]. α-Ca₄Te₅O₁₄ ^[4] consists of [Te₈O₂₂]-achter-single chains (…–(◊–Δ)–◊–◊–(◊–Δ)–◊–◊–…) as well as isolated [TeO₃] groups. The high-pressure β-Ca₄Te₅O₁₄ ^[5]is formed by isolated [Te₃O₈]- and [TeO₃] groups.

[1] Christy, A. G., Mills, S. J. & Kampf, A. R. (2016). Miner. Mag. 80, 415–545. [2] Stöger, B. & Weil, M. (2013). Miner. Petrol. 107, 253–263. [3] Kraemer, V. & Brandt, G.; (1985). Acta Cryst. C41, 1152-1154. [4] Weil, M. (2004). Solid State Sci. 6, 29-37. [5] Weil, M., Heymann, G. & Huppertz, H. (2016). Eur. J. Inorg. Chem. pp. 3574-3579.

The X-ray centre of the TU Wien is acknowledged for providing access to the single-crystal and powder X-ray diffractometers. The Christiana Hörbiger foundation is acknowledged for financial support by funding the Christiana Hörbiger award.

Arsenic(III) oxide has been known to form stoichiometric compounds with potassium and ammonium halides since the 19^th century but they have not been structurally charaterized until the middle of the 20^th century[1-4]. It was found that the compounds are intercalation compounds in which like-charged ions form alternating layers which are separated by electroneutral As₂O₃ layers (see Figure 1). This type of compounds have been found in nature as minerals, for instance, lucabindiite [5]. In case of intercalates with ammonium and potassium cations the layers are hexagonal and non corrugated, whereas for smaller sodium cations the arsenic(III) oxide layers are corrugated and exhibit lower symmetry. Herein, we present the synthesis methods and structural charaterization of the first As₂O₃ intercalates with potassium, rubidium and cesium chlorides containing water molecules in their crystal structure: MCl·As₂O₃·½H₂O (for M = K, Rb, Cs) and KCl·As₂O₃·3H₂O. The compounds are not only studied by single-crystal X-ray diffraction but also by solid state NMR spectroscopy and ATR-FTIR. The crystal structure determination of KCl·As₂O₃·½H₂O permitted for a correction proposal of NH₄Cl·As₂O₃·½H₂O crystal structure.

[1] Rüdorff, F. (1886). Ber. Dtsch. Chem. Ges. 19, 2668–2679.

[2] Edstrand, M. & Blomqvist, G. (1955). Arkiv för kemi. 8, 245–256. [3] Pertlik, F. (1987). J. Solid State Chem. 70, 225–228.

[4] Pertlik, F. (1988). Monatsh. Chem. 119, 451–456.

[5] Garavelli, A., Mitolo, D., Pinto, D. & Vurro, F. (2013). Am. Mineral. 98, 470–477.

One of the defining issues in the nuclear industry's long-term development is the long-term storage of high-level waste (HLW). Preserving matrices with a complex of unique physicomechanical and chemical properties should be used to immobilization HLW. Currently, aluminophosphate and borosilicate glasses are uмsed as such matrices. Their disadvantages are low capacity for waste (4–15 wt.%), High solubility in water, rapid crystallization, deterioration of protective properties over time. It is proposed to use crystal matrices as an alternative to glasses. The study of the ternary system NdO1.5-TiO2-ZrO2 is necessary to predict the compositions of ceramics promising as matrices for the rare-earth-actinide fraction of high-level waste (HLW). By solid-phase synthesis by sintering in a muffle furnace, 6 samples were obtained with a percentage along the line of 60 wt% NdO1.5 with variable compositions of TiO2-ZrO2, and 6 samples with a percentage along the line of 35 wt% NdO1.5 with a variable composition of TiO2-ZrO2, at temperatures of 1450⁰С and 1500⁰С.
The X-ray phase analysis was carried out on an Empyrean Malvern Panalytical X-ray powder diffractometer (CuKα, 40 kV, 20 mA, 0.02 ° step), a JSM_5610LV scanning electron microscope with a ULTIM MAX 100 energy dispersive spectrometer (SEM / EDS). The phase structure was determined by comparing the experimental X-ray diffraction patterns with the standards from the database.
X-ray phase analysis of the samples showed that at a temperature of 1450⁰C for six samples with 60 wt% NdO1.5 with variable TiO2-ZrO2 compositions, the formation of phases does not occur completely and require higher temperatures, and on the 35 wt% NdO1.5 13% ZrO2 line and 52% TiO2 is assumed to form a eutectic region. A preliminary SEM analysis confirmed this. More detailed results of the analysis of samples will be shown on the stand.

Ni₂MnGa is a widely studied system due to its interesting properties related to the magnetic shape memory phenomena. The compounds based on Ni-Mn-Ga system have also an interesting application potential as the micropumps or the sensors [1, 2]. Their shape memory properties are connected to the martensitic transformation, during which the high-temperature cubic phase (austenite) undergoes a transformation to the low-temperature phase with a lower symmetry (martensite) [3].

As a consequence of a large magnetic anisotropy and a high mobility of the internal regions (so called twin variants/twinned domains) magnetically induced reorientation could be achieved - it is more energeticaly preferable to reorient the whole unit cell than to rotate magnetic moments. A similar structural reorientation could be achieved by the application of an external mechanical force in tension or compression.

In our previous studies [3, 4], the high resolution reciprocal space mapping with x-ray diffraction proved itself as a good tool to study the structure in Ni₂MnGa samples which could contain several twinned domains due to the shape memory effects. The reciprocal space mapping helps to distiguish between the Bragg reflections corresponding to individual twins. Moreover, reciprocal space mapping allows the precise study of the lattice parameters and a possible modulation in the structure.

Our goal was to study the structure during the reorientation by x-ray diffraction in-situ in the applied tension. For this purpose, we mounted the tensile stage (possible load up to 4 kN) inside the diffractometer. The studied specimen was Ni₅₀Mn₂₈Ga₂₂ with martensitic structure at the room temperature. Besides the lattice parameters and volume ratios of individual twin variants in the various tension, the measurement revealed that the results differ in dependence on the way how the sample is hold inside the stage. Holding directly with clamps allows almost full structural reorientation at approximately 10 MPa, but the sample cracks when the twin boundary reached the place on the sample hold by the clamps. Holding by a glue prevented the reorientation and the full reorientation did not occur up to 20 MPa.

[1] A. R. Smith, et al., Microfluidic. Nanofluidics, 18 (2005), p. 1255, doi: 10.1007/s10404-014-1524-6

[2] A. Hobza, et al., Sensor. Actuator. A, 269 (2018), p. 137, doi: 10.1016/j.sna.2017.11.002

[3] O. Heczko, et al., Acta Mater., 115 (2016), pp. 250-258, doi: 10.1016/j.actamat.2016.05.047

[4] P. Cejpek, et al., J. Alloys Compd., 855 (2021) 157327, doi: 10.1016/j.jallcom.2020.157327

Borosilicate mineral tourmaline is one of the most widespread minerals in nature, one of the most popular gems and promising piezoelectric, adsorption material [1,2]. Synthetic Ga,Ge-rich analogue is structure model of tourmalines at high pressure. This work presents the results of Mössbauer studies of Ga,Ge-rich tourmaline crystals which contain a significant iron content. The crystals were grown in hydrothermal boric, boric-alkaline, boric-fluoride solutions at 650 ˚С and 100 MPa [3,4]. The chemical composition of the five studied tourmaline crystals in atoms per formula unit, calculated based on the 15 (T + Y + Z) atoms, is shown in Table 1.

The ⁵⁷Fe Mössbauer absorption spectra were measured at room temperature on a standard MS-1104Em spectrometer with a ⁵⁷Co (Rh) source. The structural and electronic states of iron ions have been studied and refined. A comparison is made with the results of X-ray diffraction measurements.

This work was supported by the Russian Ministry of Science and Higher Education under the Research Program AAAA-A18-118020590150-6 within the State assignment of D.S. Korzhinskii Institute of Experimental Mineralogy RAS - in part of crystal growth; and under the Research Program АААА-А20-120022890091-8 within the State assignment of the FSRC “Crystallography and Photonics” of RAS - in part of Mössbauer spectroscopy.

[1] Wang, C. P.; Wu, J. Z.; Sun, H. W.; Wang, T.; Liu, H. B.; Chang, Y. Adsorption of Pb(II) Ion from Aqueous Solutions by Tourmaline as a Novel Adsorbent. Ind. Eng. Chem. Res. 2011, 50 (14), 8515–8523. https://doi.org/10.1021/ie102520w.

[2] Shekhar Pandey, C.; Schreuer, J. Elastic and Piezoelectric Constants of Tourmaline Single Crystals at Non-Ambient Temperatures Determined by Resonant Ultrasound Spectroscopy. J. Appl. Phys. 2012, 111 (1). https://doi.org/10.1063/1.3673820.

[3] Setkova, T. V.; Balitsky, V. S.; Shapovalov, Y. B. Experimental Study of the Stability and Synthesis of the Tourmaline Supergroup Minerals. Geochemistry Int. 2019, 57 (10), 1082–1094. https://doi.org/10.1134/S0016702919100094.

[4] Pushcharovsky, D. Y.; Zubkova, N. V.; Setkova, T. V.; Balitskii, V. S.; Nekrasov, A. N.; Nesterova, V. A. (Ga,Ge)-Analogue of Tourmaline: Crystal Structure and Composition. Crystallogr. Reports 2020, 65 (6), 849–856. https://doi.org/10.1134/S1063774520060279.

The present investigation describes the synthesis and structural study of a metal-zinc ligand [ZnL.H2O], which was used to generate three dimensional supramolecular complex formulated as [Y{Zn(L)(SCN)}(SCN)2].[Y{Zn(L)(SCN)}2(DMF)2].(NO3). The title compound crystallizes in the triclinic space group P-1 with the following unit cell parameters: a = 14.8987(7) Å, b = 15.6725(8) Å, c = 19.2339(10) Å, α = 94.610(4)°, β = 103.857(4)°, γ = 101.473(4)°, V = 4234.4(4) Å3, Z = 2, R1 = 0.063 and wR2 = 0.96. For this compound, the structure reveals that one heterodinuclear unit [Y{Zn(L)(SCN)}(SCN)2] is co-crystallized with a heterotrinuclear unit [Y{Zn(L)(SCN)}2(DMF)2].(NO3). In the dinuclear moiety, the organic molecule acts as a hexadentate ligand and in the trinuclear unit, it acts as a pentadentate ligand with one of the oxygen methoxy group remaining uncoordinated. In both units the coordination environment of the zinc metal can be described as distorted square pyramidal. In the dinuclear unit the Y(III) is hexacoordinated while it is octacoordinated in the trinuclear unit. The environment of the Y(III) can be described as a distorted octahedral geometry in the dinuclear and as a distorted square antiprism in the trinuclear units respectively.

Schiff base compounds have been recognized as privileged of organic molecules, because of their interesting and important properties, they are able to coordinate with various metals and stabilize them. It’s an important special centre of attraction in many areas like biological, clinical, medicinal, analytical and pharmacological field [1]. They are also used in analytical medicinal and polymer chemistry. The azomethine (C=N) linkage in Schiff bases is significant in determining the mechanism of transamination and resamination reactions in biological systems[2], and it has been suggested that the azomethine group is responsible of the biological activities of Schiff bases molecules. Schiff bases ligands with chelating abilities have been recognized as privileged ligands to form stable complexes with a large variety of transition metals [3].

Herein, newly synthesized mononuclear copper(II) and zinc(II) complexes containing an azo Schiff base ligand (L), prepared by condensation of 2-hydroxy-5 (otolyldiazenyl)benzaldehyde and propylamine, were obtained and then characterized using infrared and NMR spectroscopies, mass spectrometry and X-ray diffraction. Ligand L behaves as a bidentate chelate by coordinating through deprotonated phenolic oxygen and azomethine nitrogen. The copper and zinc complexes crystallize in triclinic and orthorhombic systems, respectively, with space groups P-1 and Pca21. In these complexes, the Cu(II) ion is in a square planar geometry while the Zn(II) ion is in a distorted tetrahedral environment. The photochemical behaviors of ligand L, [Cu(L)2] and [Zn(L)2] were investigated.

[1] P. Przybylski, A. Huczynski, K. Pyta, B. Brzezinski, and F. Bartl, “Biological Properties of Schiff Bases and Azo Derivatives of Phenols,” pp. 124–148, 2009.

[2] P. P. Dholakiya and M. N. Patel, “Synthesis and Reactivity in Inorganic and Metal- Organic Chemistry Metal Complexes : Preparation , Magnetic , Spectral , and Biocidal Studies of Some Mixed ‐ Ligand Complexes with Schiff Bases Containing NO and NN Donor Atoms,” no. April 2015, pp. 37–41, 2010.

[3] A. Corma, H. Garcia, F. X. Llabrés, and I. Xamena, “Engineering
metal organic frameworks for heterogeneous catalysis,” Chemical Reviews, vol. 110, p. 4606, 2010

Geopolymers based on clay materials from Burkina Faso were developed and then characterized for use in building. The results of the characterization of the clay mineral material referenced TAN as well as its calcined forms have shown by several analysis techniques (XRD, IR, ICP-AES) that TAN contains kaolinite (71%), quartz (20%), illite (4%) and goethite (2%). TAN clay and its calcined forms are each mixed with the alkaline solution (sodium hydroxide solution 8 mol. L^-1) in a mass ratio (alkaline solution/clay) ranging from 0.33 to 0.36. The results of the mechanical and mineralogical tests of the geopolymers produced showed that GP-MK₀ produced had the best performance favorable for its use in construction. Indeed, its linear shrinkage (3.44%) is low and the compressive strength (22.50 MPa) is greater than 4 MPa. This performance of GP-MK₀ is due to the formation of a phase rich in silica and alumina (Na₂(AlSiO₄)₆(OH)₂. 2H₂O).

The whitlockite-type compounds have a structure favorable for the introduction of dopant ions, which led to the implementation or enhancement of functional properties. The use of different doping methods can significantly affect the concentration and structural location of activator ions in the crystal matrix, and hence the properties of the material. This was the motivation for the work. The main research methods are X-ray structural analysis (diffractometers and synchrotron, room temperature and 100 K; statistical structure) and X-ray absorption spectroscopy (synchrotron; local structure).

In the idealized whitlockite structure Ca₃(PO₄)₂ (space group R3c, Z = 18) with the composition (Ca1₁₈Ca2₁₈Ca3₁₈)(P1₁₈P2₁₈)O₁₄₄, Ca1 and Ca3 atoms are located in two-capped trigonal prisms (CN = 8; CN is a coordination number) and Ca2 atoms form mono-capped trigonal prisms (CN = 7), P1 and P2 atoms being in tetrahedra (CN = 4). In the whitlockite-type structure Ca₃(VO₄)₂ (CVO; space group R3c, Z = 21) with the composition [Ca1₁₈Ca2₁₈Ca3₁₈Ca4₆(Ca5_2.65)(Ca5А_0.35)](V1₁₈V2₁₈V3₆)O₁₆₈, there are additional sites in the framework channels: Ca4 and Ca5A (octahedra; CN = 6), Ca5 (tetrahedron; CN = 4), Ca5 + Ca5A (distorted octahedron; CN = 6), and V3 (trigonal pyramid; CN = 3 + 1).

Dopant ions (up to 1.0 wt%) introduced into the melt (Czochralski method) over CVO stoichiometry are distributed over the Ca3 and Ca4 (light-green CVO:Tm and green CVO:Mn crystals) as well as Ca5 + Ca5A (CVO:Mn) crystallographic sites. The dopant ions form specific local environments: in the CVO:Tm structure, CN Tm³⁺ = 7 (octahedral coordination by O^2- ions with one additional O atom) and CN V⁵⁺ = 4.4; in the CVO:Mn structure, CN Mn³⁺ = 6 (an elongated octahedron is a tetragonal bipyramid; Jahn-Teller effect) and CN V⁵⁺ = 4. Air annealing of CVO:Mn crystals promotes the appearance of yellow-orange crystals with Mn⁴⁺ and Mn^(3+d)+ ions having octahedral coordination in the Ca3 and Ca5 sites in the structures of the lower and upper parts of the crystal boule, respectively.

High-temperature diffusion annealing of CVO crystal with the presence of Mn₂O₃ solid phase (blue-green CVO:Mn₂O₃) increases the number of sites (Ca2, Ca3, Ca4) occupied by a greater number of Mn^(2+d)+ ions with variable formal charge and tetrahedral local environment. Similar annealing of CVO with the Co₃O₄ solid phase (violet CVO:Co₃O₄) leads to the appearance of Co²⁺ ions, which, unlike CVO:Mn₂O₃, partially replace the Ca²⁺ ions in the Ca2, Ca3, Ca4, Ca5, and Ca5A crystallographic sites.

The bands revealed on the absorption spectra were assigned to Tm, Co, and Mn ions having different formal charges and different local environments in the CVO structure.

Lead zirconate titanate, PbZr_1-xTi_xO₃ (PZT), is a ceramic perovskite material that has exceptional striking piezoelectric properties at the morphotropic phase boundary (MPB) showing a piezoelectric response (d₃₃) of 200-600 pC/N [1]. This compound plays an important role in industry and has many commercial applications [2-3]. However, the toxicity of lead has spurred considerable interest in the discovery of Pb-free ferroelectric materials. Here, we present our results on two different Pb-free piezoelectric systems: 1) solid solutions between BaTiO₃ (BT) and BiInO₃ (BI), and 2) BaZr_0.2Ti_0.8O₃ (BZT) and Ba_0.7Ca_0.3TiO₃ (BCT).

1) Solid solutions between BaTiO₃ and BiInO₃: Bismuth based perovskites are established as good ferroelectric materials, but it is still necessary to improve the piezoelectric properties of Bi-based perovskites to compete with the exceptional ferroelectric properties of PZT. To fully understand the reason of these maximized physical properties at the MPB, it is crucial to study the structure in detail. For the system (1-x)BT – (x)BI, we study the electromechanical properties and the structure of the solid solution between the Bi-based material BI with orthorhombic space group Pna2₁ and the classical piezoelectric material BT with tetragonal structure P4mm, in the region 0.03 ≤ x ≤ 0.12. Based on a structural analysis study previously carried out by Datta et al. [4], it was predicted that there is an MPB created by a polarization extension mechanism for the system at x = 0.1. In our work, based on Rietveld analysis performed on neutron and synchrotron radiation X-ray diffraction data, we have found that a gradual structural phase transition takes place from a polar tetragonal structure (P4mm) and passes through two regions of coexisting phases: 1) P4mm + R3m in the range 0.03 ≤ x ≤ 0.075, and 2) + R3m for 0.10 ≤ x ≤ 0.12. The properties also transition from ferroelectric (x ≤ 0.03) to relaxor ferroelectric (x ≥ 0.05) as the dielectric permittivity maximum becomes temperature and frequency dependent. This transition was also confirmed via polarization-electric field measurements as well as strain-electric field measurements. At the critical composition of x = 0.065, a moderate strain of ~ 0.104%, and an effective piezoelectric coefficient (d₃₃*) of 260 pm/V were observed. The original purpose of this study was to demonstrate the polarization extension mechanism as predicted in the literature, but due to the ferroelectric to relaxor transition, this mechanism was not found to be present in this system. However, this demonstrates that BaTiO₃-based lead-free ceramics could be modified to obtain enhanced electromechanical properties for actuator applications [5].

2) Solid solutions between BaZr_0.2Ti_0.8O₃ and Ba_0.7Ca_0.3TiO₃: The solid solution (1-x)BZT-xBCT is the first Pb-free piezoelectric material with a significantly high enough d₃₃ ~ 620 pC/N at the MPB at x = 0.50, that has the potential to replace the industry standard PZT in certain applications [6]. So far, lots of studies have focused mainly in investigating the physical properties. However, the two structural characterization works of the structure at the MPB for BZT-xBCT, using solely synchrotron X-ray diffraction data, yield different results [7-8]. Here, we re-investigate the phase diagram of (1-x)BZT-xBCT as a function of temperature using high quality neutron powder diffraction data collected at POWGEN at the Spallation Neutron Source and applying the Rietveld method. We study the composition x = 0.50 at the MPB, one composition in the rhombohedral range (x = 0.40), and another composition in the tetragonal range (x = 0.60). Neutron diffraction is a powerful tool to have more accurate information about the light elements such as oxygens. So, this work is crucial to investigate the octahedral tilts of (1-x)BZT-xBCT materials, and further understand how the structure has an impact on their physical properties. We expect to obtain a detailed description of the structures at different temperatures, solve the debate of the symmetry at the MPB, and build a phase diagram.

[1] Damjanovic, D., Klein, N., Li, J., Porokhonskyy, V. (2010) Funct. Mater. Lett. 3 (1):5–13.

[2] Panda, K. P. (2009) J. Mater. Sci. 44 (19):5049–5062.

[3] Roedel, J., Jo, W., Seifert, K. T. P., Anton, E. M., Granzow, T., Damjanovic, D. (2009) J. Am. Ceram. Soc. 92 (6):1153–1177

[4] Datta, K., Suard, E., Thomas, P. A. (2010) Appl. Phys. Lett. 96 (22):221902–221903.

[5] Manjon-Sanz, A., Berger, C., Dolgos, M. R., J. Mater. Sci. (2017) 52:5309–5323.

[6] Liu, W., Ren, X. B., Phys. Rev. Lett., (2009) 103, 257602.

[7] Keeble, D. S., Benabdallah, F., Thomas, P. A., Maglione, M., Kreisel, J. (2013) Appl. Phys. Lett., 102(9) 092903.

[8] Haugen, A., Forrester, J. S., Damjanovic, D., Li, B., Bowman, K. J., Jones, J. L, (2013) J. Appl. Phys., 113, 014103.

The global demand for energy production has intensified the interest in improving the efficiency of energy generation systems. In this context, thermoelectric materials have been used to take advantage of the conversion of residual heat into electricity [1]. High efficiencies have been obtained using lead-based nano-structured thermoelectric materials, such as (PbTe) m-AgSbTe₂ systems [2]. Due to the presence of lead, a known toxic element, and tellurium, a rare element in the earth's crust, alternatives must be sought. Chemical modifications and doping of SnSe have generated interest due to its low intrinsic thermal conductivity [3]. Of such modifications, AgSn_mSbSe₂Te_m phases with m = 2 and 10 have shown values ​​of ZT = 0.1 at RT [4]. On the other hand, to enhance the Seebeck coefficient in AgSbTe₂ compounds, Bi doping has been used, which increased the ZT value by 10% [5].

Herein, we report the synthesis, characterization, and electrical properties of AgSn_m(Sb_1-xBi_x)Se_m+2 compounds, with m = 1, 2. These phases were synthesized by the ceramic method at high temperatures (Figure 1A). Rietveld refinement results indicated that the selenides consisted of phases related to NaCl-type crystal structure. The powder X-ray diffraction (XRD) patterns were refined in the Pm-3m and P4/mmm space group. The backscattered image and EDS analysis of the samples revealed that the chemical compositions were uniform throughout the scanned region. The microstructural features of the samples were analysed using HRTEM. Figure 1B shows the ED patterns for the selected areas. The results suggest the presence of regions with different symmetries at the nanoscale.

Figure 1. (A) X-ray diffraction patterns (XRD) for AgSn_m(Sb_1-xBi_x)Se_m+2 (B) HRTEM images showing electron diffraction patterns (ED) and fast fourier transforms (FFTs). The arrows indicate the dots of the reciprocal lattice, which violate the systematic absence of the Fm-3m space group.

[1] Zhang, X., & Zhao, L. D. (2015). Thermoelectric materials: Energy conversion between heat and electricity. Journal of Materiomics, 1(2), 92-105.

[2] Han, M. K., Androulakis, J., Kim, S. J., & Kanatzidis, M. G. (2012). Lead‐Free Thermoelectrics: High Figure of Merit in p‐type AgSn_mSbTe_m+2. Advanced Energy Materials, 2(1), 157-161.

[3] Zhao, L. D., Lo, S. H., Zhang, Y., Sun, H., Tan, G., Uher, C., Wolverton C., Dravid V. P. & Kanatzidis, M. G. (2014). Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals. Nature, 508(7496), 373.

[4] Figueroa-Millon, S., Álvarez-Serrano, I., Bérardan, D., & Galdámez, A. (2018). Synthesis and transport properties of p-type lead-free AgSn_mSbSe₂Te_m thermoelectric systems. Materials Chemistry and Physics, 211, 321-328.

[5] Mohanraman, R., Sankar, R., Chou, F. C., Lee, C. H., & Chen, Y. Y. (2013). Enhanced thermoelectric performance in Bi-doped p-type AgSbTe₂compounds. Journal of Applied Physics, 114(16), 163712.

Keywords: Rietveld analysis; lead-free Thermoelectric; HRTEM, Selenides

Authors are grateful for FONDECYT Project N° 1190856

Alexandrite and emerald are two gem-quality varieties of chrysoberyl (BeAl2O4) and beryl (Be3Al2Si6O18), respectively. Chrysoberyl is a multiple oxide which crystallises within orthorhombic system and space group Pmnb. Its crystalline structure is composed of O2- anions which are distortedly arranged in a cubic closed packing together with Be2+-tetrahedra and Al3+- octahedra cations; Be2+ is an inversion Ci-type site and Al3+ is divided into inversion Al1 (Ci-type) and reflexion Al2 (Cs-type) sites. Beryl is a cyclosilicate which crystallises within orthorhombic system and space group P6/mcc. Its crystalline structure is composed of Si4+ tetrahedra which are interconnected by their vortices, forming ring-like layers that are stacked. Between the Si4+-rings, layers of Be2+-tetrahedra and Al3+-octahedra cations are alternately arranged. Moreover, the senary axis of beryl is perpendicular to the planes formed by the stacked Si4+-rings and is parallel to the channels-like voids formed by the aforementioned rings. Chrysoberyl and beryl have been extensively studied and referred not only as gemstones (i.e. the role of Cr3+ as a chromophore element) but also as materials used to manufacture lasers. Alexandrite and emerald were simultaneously approached in few studies, although studied separately. Thus, there was no study nor reference about the “joint-occurrence” of emerald and alexandrite in just one “polycrystal”. Consequently, no crystallographic relation could be established in this situation, specially all the processes that could explain the hypothetical transition from orthorhombic to hexagonal symmetry or vice versa. Two minerals that “illustrate” the crystallographic relations and the transition between the orthorhombic and hexagonal symmetries, in naturally occurring minerals, are the silicates cordierite [(Mg,Fe)2Al3(AlSi5O18); space group Cccm] and indialite [Mg2Al3(AlSi5O18); space group P6/mcc], respectively. The transition between these phases occurs above 1450 ºC and is related to Fe / (Mg + Fe) ratio during the crystallisation [1]. The transition between orthorhombic to hexagonal (no matter the order) has been mainly demonstrated by epitaxial processes which are only exemplified by synthetized materials. The phase perovskite- SrIrO3 is generally synthetized within hexagonal symmetry (space group C2/c). In conditions of high pressure, this phase symmetry becomes orthorhombic (space group Pnma) due to epitaxial processes on oxide substrates with the same crystal structure of perovskite [2]. Another example of the role of epitaxy in the transition between the aforementioned symmetries is given by multiferroics of RMnO3-type (R = rare earth elements or REE). In this case, the type of REE of R site influences the symmetry: to R = La-Dy, symmetry is orthorhombic, and to R = Ho-Lu, symmetry is hexagonal. However, with the aid of epitaxial stabilization technique, orthorhombic symmetry-materials such as TbMnO3, DyMnO3 and GdMnO3 can be synthetized within hexagonal symmetry and originate high quality magnetic materials [3]. After contextualizing the state-of-art of the crystallographic

relations and transition between orthorhombic to hexagonal symmetries, this study also proves to be novel due to the rarity of the samples: natural “joint-occurrence” alexandrite + emerald polycrystals (core of alexandrite surrounded by an emerald monocrystal) from Brazil. Apart from the transition in symmetry, other relevant questions are: how to explain the transition between a silicate (emerald) and an oxide (alexandrite), or vice versa, in the same polycrystal? Why the arrangement of the inner alexandrite monocrystals varies among the samples? Which mineral phase has crystalized first and how their genesis can be explained by chemical data? In order to answer consistently to these questions and for a better knowledge of these implications, these samples are being investigated with the aid of techniques such as electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and electronic probe microanalysis (EPMA). Preliminary TEM studies show an orientation relationship between micrometer sized grains of emerald and alexandrite.

Compounds including thallium in formal negative oxidation states have been known since Zintl stated the existence of NaTl in the 1930s [1]. In the 1980s and 1990s, binary materials of alkali metal and thallium have been characterized [2] but crystal structures always suffered from severe absorption effects due to very large absorption coefficients for these kinds of materials. This fact for a long time was equitable to the physical frontier of the method of structure determination for these element combinations. Nowadays, for these compounds, which were formerly assumed to behave rather as a primary beam stop, very good data sets can be realized due to highly resolving detectors and intensive x-ray sources [3]. This is the pre-condition for a renaissance of investigations on alkali metal thallides. The amount of alkali metal does not readily suggest the formed thallium sublattice. In fact, one can find transitions between different type structures in dependence of the more electropositive element involved. Looking at the already known alkali metal thallide compounds, it is striking that some gaps still have remained [4]. For example, in A₁₅Tl₂₇ (A= Rb, Cs) [5] and K₄₉Tl₁₀₈ [6] type structures, the ratio of alkali metal : thallium is very similar, but the respective crystal structures severely differ. While K₄₉Tl₁₀₈ is a complex cubic compound, A₁₅Tl₂₇ involves Tl₁₁⁷⁻ clusters and two-dimensional thallium layers. Here, partially occupied alkali metal Wyckoff sites allow for the discussion of their effect on the observed thallium sublattice. Additionally, the possibility of partially replacing cesium by thallium could be demonstrated for the new binary material Cs_14.53Tl_28.4 in terms of an ordered substitution variant of Cs₁₅Tl₂₇.

[1] E. Zintl and W. Dullenkopf, Z. phys. Chem. 1932, B16, 195-205; S. M. Tiefenthaler, M. Schlosser, F. Pielnhofer, I. G. Shenderovich, A. Pfitzner and S. Gärtner, Z.Anorg.Allg. Chem. 2020, 646, 82-87; S. Tiefenthaler, N. Korber and S. Gärtner, Materials 2019, 12.

[2] J. D. Corbett, Angew. Chem. Int. Ed. 2000, 39, 670-690.

[3] S. Gärtner, S. Tiefenthaler, N. Korber, S. Stempfhuber and B. Hischa, Crystals 2018, 8.

[4] S. Gärtner, Crystals 2020, 10(11), 1013

[5] Z. C. Dong and J. D. Corbett, Inorg. Chem. 1996, 35, 1444-1450

[6] G. Cordier, V. Müller and R. Fröhlich, Z. Kristallogr. 1993, 203, 148-149.

Keywords: x-ray structure determination; high absorption coefficients; thallides; alkali metal; Zintl phases.

In recent years, many studies have been carried out on cement and its phases to understand the morphology, and to control the mineralogy of this material; due to the great position it has become globally occupied. This material is formed from a synthetic rock called clinker; tricalcium silicate (Ca3SiO5 or C3S) its major constituent present a concentration from 40% to 70%, and its solid solution with various impurities is called alite. Impure C3S exhibits seven polymorphs from ambient temperature to 1500°C; three forms triclinic (T1, T2, T3), three monoclinic (M1, M2, M3) and one shape rhombohedral (R). At room temperature, impurities stabilize some of the high temperature forms of the pure compound. Those forms are related by transformation matrix determined in this article. The aim of the present paper is to investigate the structural modulations of alite.

The utilization of transition-metal based layered compounds is already established in industrial applications. Considering a combination with mixed-anion systems creates an extended pool of materials that can be screened for superior functionality. The option for post-synthetic alterations to the system offers further possibilities to control properties and gives access to kinetically stable products.

Previous works explored the possibility to influence magnetism and reversibly insert lithium in the oxysulfides Sr₂MnO₂Cu_2m-δS_m+1 (δ ≈ 0.5).[1-3] While trying to minimize the weight of these materials the compound Ca_xSr_2-xMnO₂Cu_4-δS₃ (x = 1; δ ≈ 0.5) was obtained by ceramic synthesis. The compound consists of antifluorite-type copper sulfide double layers exhibiting a copper deficiency and square planar MnO₂ sheets separated by the alkaline-earth cations. Magnetic susceptibility measurements show high-temperature Curie-Weiss behavior and a positive Weiss constant of 9(2) K suggests that the net exchange interactions are predominantly ferromagnetic. The effective magnetic moment of μ_eff = 5.63(2) μ_B indicates the oxidation of manganese to a (2+δ)⁺ state. Oxidative copper deintercalation provides control over the oxidation state of Mn, while replacing Cu⁺ by Li⁺ under reductive ion exchange conditions (sse Fig. 1) also makes the material interesting for battery applications.

Palladseite, Pd₁₇Se₁₅ was described as a new mineral by Davis et al. [1] from residual concentrates from gold washing at Itabira, Minais Gerais, Brazil. Palladseite has an ideal chemical composition of Pd₁₇Se₁₅. Ag, Cu, Hg and Pt are common elements to occur in the palladseite structure and are regarded as non-essential elements for palladseite; e.g. Cabral and Lehmann [2] indicated 3.89 wt.% of Hg and 4.43 wt.% of Ag for palladseite-like mineral from Gongo Soco, Brazil. Crystal structure of synthetic Pd₁₇Se₁₅ was solved by Geller [3].

In order to explain the incorporation of reported significant amounts of Ag, Cu, Hg, Pt and Te and define the range of their solubility in the palladseite structure, an experimental study of solubility of above-mentioned elements in the synthetic analogue of palladseite at 400 °C was performed. Silica glass tube technique was used. To document the impact of these elements on the palladseite crystal structure, Rietveld refinement analysis of powder X-ray diffraction data of experimental products was carried out.

Palladseite (Pd₁₇Se₁₅) crystalizes in the Pm-3m space group (a = 10.607 Å) and contains four Pd and three Se sites. It has a framework crystal structure formed by three types of polyhedra: [PdSe₆] octahedra, [PdSe₄] squares and [PdSe₄] flattened tetrahedra. Three way of substitution mechanism were revealed to occur in the palladseite structure. Cu, Ag and Hg enter the palladseite structure in a significant amount (e.g. up to 8.8 wt% of Hg) and occupy a new position 3d of the Pm-3m space group, which was empty in pure Pd₁₇Se₁₅. As a consequence, Pd occupancy of adjacent [Pd(4)Se₆] octahedron is reduced to 0.5 for Cu and Ag - bearing palladseite. Incorporation of Hg cases vacancy of this [Pd(4)Se₆] position. Contrary to that, Pt substitutes Pd at the Pd(2) position in the palladseite structure and shows square-planar coordination by Se atoms. This is in agreement with expected coordination preference of Pt. Te enters palladseite structure in an significant amount (6.50 wt. %) and substitutes Se atoms without further modification of the palladseite structure.

Incorporation of Cu, Ag and Hg to the palladseite causes significant changes of its powder X-ray diffraction pattern and hence can be easily detected.

Figure 1. Crystal structure of substituted palladseite (M = Ag, Cu or Hg). For Hg-bearing palladseite, the Pd(4) site is empty. Note three types of coordination polyhedra including [PdSe₄] squares (yellow), [PdSe₄] flattened tetrahedra (green) and [PdSe₆] octahedra (orange).

[1] Davis, R.J., Clark, A.M., Criddle, A.J. (1977). Mineral Mag. 41, 123. [2] Cabral, A.R., Lehmann, B. (2007). Ore Geology Reviews, 32, 681. [3] Geller, S. (1962) Acta Cryst. 15, 713.

Keywords: Pd17Se15, palladseite, Rietlved refinement, minerals, substitutions

This work was supported by an internal project of the Czech Geological Survey no. 311020.

Apatite is a name currently used for a mineral supergroup which contains over 40 mineral species with a similar atomic framework structure. According to occupancy of the two metal-cation sites and the tetrahedral site in the crystal structure, the apatite supergroup is subdivided into five groups. One of these groups is the apatite group where the metal sites are occupied by the same dominant element: Ca, Pb, Mn or Sr, and the tetrahedral site is occupied by P, As, or V [1,2]. In common use, the name apatite comprises the calcium phosphate minerals in which the halogen site is occupied by the F^-, Cl^- or OH^- anions in the form of columns along the edges of the unit cell. If the column site is dominated by F, the apatite is referred to as fluorapatite which crystallizes in space group P6₃/m.

On the basis of a multipole refinement from high resolution x-ray diffraction data collected up to 0.4 Å, a quantitative experimental charge density distribution has been determined for natural (n) and synthetic analog (s) of fluorapatite. The Bader charges [3] for all atoms were determined from electron density integration within atomic basins (Fig. 1), q^Ca(1)_(n)=+1.6e; q^Ca(1)_(s)=+1.5e; q^Ca(2)_(n)=+1.5e; q^Ca(2)_(s)=+1.6e; q^F_(n)=-0.4e; q^F_(s)=-0.4e; q^P_(n)=+3.4e q^P_(s)=+3.5e; q^O(1)_(n)=-1.5e; q^O(1)_(s)=-1.5e; q^O(2)_(n)=-1.3e; q^O(2)_(s)=-1.4e; q^O(3)_(n)=-1.3e; q^O(3)_(s)=-1.4e. The topological analysis of the electron density distribution showed, apart from the presence of strong Ca…F, Ca…O, P…O interactions, weak O…O interactions associated to charge-shift bonding [4,5].

The crystal structure model and the electron density distribution of fluorapatite serves as a reference for ongoing studies of the substituted F-Cl; F-OH and Cl-OH apatite series.

Figure 1. The atomic basin representation of all atoms from assymetric unit of fluorapatite. Atomic basins are surrounded by atoms from their closest neighbourhood.

[1] Pasero M., Kampf A.R., Ferraris C., Pekov I.V., Rakovan J.F., White T.J. (2010). European Journal of Mineralogy, 22, 163-179.

[2] Hughes J.M., Rakovan J.F. (2015). Elements, 11, 165-170.

[3] Bader, R. F. W. (1994). Atoms in Molecules: A Quantum Theory Clarendon Press.

[4] Shaik, S., Danovich, D., Wu, W. & Hiberty, P. C. (2009). Nat. Chem. 1, 443–449.

[5] Stachowicz, M., Malinska, M., Parafiniuk, J. & Woźniak, K. (2017). Acta Crystallogr. Sect. B Struct. Sci. Cryst. Eng. Mater. 73, 643–653.

KW acknowledges a financial support within the Polish National Science Centre (NCN) OPUS17 grant - decision DEC-2019/33/ B/ST10/02671.

Oxide materials that have high temperature stability are potential candidates for waste heat energy conversion applications. The phase diagrams of the Ca-M-Co-O (M=Sr, La, Sm, Eu, Gd, and Ho) systems were determined. These diagrams offer compatibility relationships in the ternary oxide systems that are essential for processing and for the understanding of thermoelectric properties. In these systems, in addition to the well-known (Ca, M)₃Co₄O₉ phase (with misfit layered structure) that has excellent thermoelectric properties, other low-dimensional phases include the homologous series, A_n+2Co_nCo’O_3n+3 (where A=Ca, and (Ca, Sr)). While the members of the A_n+2Co_nCo’O_3n+3 series have reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical conductivity needs to be increased in order to achieve higher figure of merit (ZT) values. This paper discusses our phase equilibria/structure/property studies of selected cobaltates in the Ca-M-Co-O systems.

The excellent optical properties and versatile crystal chemistry make borates outstanding candidates for application as nonlinear optical (NLO) materials. These properties are enhanced by introducing “extra” anions, halides yielding the best performances. Introducing halides increases the abundance of non-centrosymmetric structures. As constituents of ionic lattices, halide ions readily contribute to the formation of salt-inclusion structures, which are generally defined as structures comprised of two parts, of varied dimensionality, exhibiting one, covalent, and the other, ionic character of chemical bonding. The ionic part generally fills the channels and/or cavities of porous covalent networks, while the cases where these parts constitute interpenetrating frameworks are scarce.

We have successfully synthesized and characterized several new silver halide borates, Ag₄B₄O₇X₂ (X = Br, I), Ag₃B₆O₁₀I, and Ag₄B₇O₁₂Br, which were prepared by slow cooling stoichiometric melts jr glass crystallization. The crystal structure of Ag₄B₄O₇X₂ is non-centrosymmetric (s.g. P6₁22) and comprised of coalesced pentaborate groups or so-called “kernite” chains 5B : 2∆3□ : (<∆2□ >–<∆2□ >–)sharing vertices to form a framework with equal content of BO₃ triangles and BO₄ tetrahedra. Their thermal expansion is strongly anisotropic due to the orientation of rigid kernite chains aligned parallel to ab plane. The calculated band structures indicate that Ag₄B₄O₇Br₂ and Ag₄B₄O₇I₂ are direct semiconductors with a band gap of about 2.0 and 2.4 eV, respectively.

The crystal structure of Ag₄B₇O₁₂Br is triclinic (s.g. P-1), and formed by unique layers comprised of vertex-sharing triborate and tetraborate groups. Ag₃B₆O₁₀I is orthorhombic (s.g. Pnma) and isostructural to Na₃B₆O₁₀Br. The structure contains two interpenetrating frameworks one of them comprised of vertex shearing B₆O₁₃ hexaborate groups; the metal-halide anti-ReO₃ framework is strongly distorted towards formation of isolated Ag₃I²⁺ groups with relatively short Ag×××Ag contacts indicative of “argentophilic” interactions.

Crystal structures of these borates are comprised of two porous interpenetrating frameworks and demonstrate a further development of the “salt-inclusion” architecture toward a “covalent-inclusion” structure. The AgX sublattices exhibit strong anharmonic vibrations. The joint-probability density function was calculated from the inverse Fourier transform of the anharmonic ADPs approximated by the third-order expansion of the Gram–Charlier series [1]. This indicates the presence of structural analogies between borate nitrates and borate halides and indicates further directions in the search for new compounds in these families.

This work was financially supported by the Russian Science Foundation through Grant 21-73-00216.

(1) Kuhs, W. F. (1992). Acta Cryst. A109, 80–98.

Ambiphilic molecules such as phosphine-borane and amine-borane have drawn huge interest recently. Amine borane in particular, has been widely known to be efficient in sensing of hazardous anions such as fluoride and cyanide which can monitored using the fluorimetry. In addition, the coordination properties of P-/N- donor containing borane compounds with various coinage metals had a significant impact in their luminescence properties which can be utilized for various biological or electronic applications.^1,2

Erstwhile, we have reported a series of backbone heteroatom-substituted imidazoles (SPh, PPh₂, SiMe₃, O₂BPh, I, Br) as a precursors for the synthesis of functionalized NHC-metal complexes.³ In this work, synthesis of ambiphilic ligand on metal halogen exchange with a Lewis acidic BMes₂ (Mes = mesityl) at the backbone of the imidazole was achieved.⁴ Among them, two isomeric boron-phosphine functionalized imidazoles, monoboron-functionalized imidazoles, and its corresponding imidazolium salts were prepared and thoroughly characterized. Their solid-state structures reveals a dimeric B−N adduct that six-membered [C−B− N]2 ring, and a tetrameric B−N adduct that forms an interesting 16-membered macrocycle, among various other monomeric BMes₂-substituted imidazoles. The fluoride sensing properties of the synthesised BMes₂-containing imidazoles were studied using UV−vis and fluorescence spectroscopy.

The ideal separation provided by P^N-type ligand gives room for metal-metal interaction upon the coordination with coinage metals which in turn lead to bright luminescent. Here, the P^N type ligand synthesised was treated with CuX(X=Br,I) to give L₂Cu₄I₄-type luminescent metal complexes. In addition, metalation of the P^N ligand with other coinage metal salts such as AgX (X=OTf, NO₃), AuCl.SMe₂ was also tried. Upon crystalisation, their solid state structures reveal the cleavage of C-5 BMes₂

Metallothermally reduced deep-sea nodules from Clarion-Clipperton Zone (Pacific Ocean) are investigated in this study. The aim is to prepare “natural alloy”, to construct as simply as possible way to reduce nodules into the usable alloy without wasting the energy, mainly to avoid the purification of individual metals. Here used nodules contain manganese as the dominant element, whereas iron, nickel and copper are other major constituents besides aluminium and silicon. The deepest investigated is the aluminothermic process [1], nevertheless the other reducing metals - titanium and silicon - are investigated too.

The nodules were reduced and annealed alloys at 700 °C with various excess of aluminium (0 %, 10 %, and 20 %). Using XRD there were found three, five and eight phases, some of them not listed in databases. Some other minor phases as sulphide MnS were found using SEM with EBSD/EDS coupled detectors.

There is a couple of interesting points. The formation of main manganese rich phase, which develops from β-Mn₆₆Ni₂₀Si₁₄ phase (P2₁3 space group) at 0 % of excess to β-Mn phase (P4₁32 space group) at 10 % of excess and to α-Mn phase (I-43m space group) at 20 % of excess. The separation of Mn₂FeSi and Mn₂FeAl phases. Those phases were just recently confirmed experimentally to exist.

[1] Novák P., Nguyen H. V., Šulcová L., Kopeček J., Laufek F., Tsepeleva A., Dvořák P. & Michalcová A. (2021) Materials 14, 561.

Keywords: deep-sea nodules, metal reduction, aluminothermy, EBSD, manganese

We acknowledge Czech Science Foundation project 20-15217S for support and CzechNanoLab Research Infrastructure (LM2018110) by MEYS CR for SEM infrastructure support.

What should be investigated to comprehend a journey, life, or any dynamic phenomenon? Apart from the input and outcome, the observable steps in-between are pivotal in understanding the whole process and getting perspectives for further utilization. The struggle in rationalizing crystallization, a supramolecular reaction, for the targeted design of functional materials is to recognize the underlined possible pathways. The task is significantly challenging due to the obscurity of well-defined links between synthesis, structure, and property. However, Polyoxometalates (POM), the intermediate soluble molecular analogues of the bulk oxides, may provide some insights. These anionic oxo-clusters, typically of V, Mo, and W, have been of interest to researchers in the field of solid-state and materials chemistry not only due to their promising potential in near-future applications but also for the fundamental acumens they can provide into surface properties of bulk oxides. Out of many possible POM architectures, our choice of the Anderson Evans archetype was based on its structural versatility tunable at the molecular level. Our interest further strengthened upon noticing the ruby-like emission from the Cr-analogue of the archetype {Cr(OH)₆Mo₆O₁₈}^3-, even when other luminescent species were present. We then ventured on the quest of incorporating luminescent lanthanide counter cations into {Cr(OH)₆Mo₆O₁₈}^3- as well as the photo-physically silent {Al(OH)₆Mo₆O₁₈}^3- for understanding the variations in properties of the landscape of structures associated with changes in synthetic parameters. The poster presents a multidimensional structural landscape of lanthanide coordinated solids based on the Anderson-Evans cluster and the investigation of its photoluminescent properties.