Conference Agenda

The crystallisation of various materials from solution is an important area of study in the field of in situ X‑ray diffraction. Beamline I12 at Diamond synchrotron offers the improved experimental capabilities for in situ investigation of the large-scale synthesis process in unprecedented detail [1]. Time-resolved monochromatic high energy X-ray diffraction on the Beamline I12 is a fast and efficient method for investigation of crystallization allowing the detection of crystalline intermediates, formulating an idea about the crystallization mechanism, and the assessment of individual reaction parameters, i.e., reaction rate constants and activation energies. Thus, the optimization of the synthesis conditions of new compounds can be achieved. The high X-ray flux on the beamline I12 allows real-time monitoring the synthesis in the large containers, including standard laboratory metal autoclaves. Using monochromatic X-rays for the synchrotron experiments produces the high-quality diffraction data that permits the full structural refinements to be undertaken on metastable materials observed during the reaction.

The simplest experimental setup for low temperature in situ diffraction experiments is a metal heating block, which allows measurements during the synthesis from room temperature to approx. 90^oC. It can be used with magnetic hotplate stirrer, allowing to mix substance during the measurements providing the homogeneous distribution of material in the reaction tube. For synthesis at temperatures close to the room temperature, the remotely controlled syringe pump can be used allowing simultaneous or sequential adding the reactants, thus permitting the investigation of the reaction in the controlled way from the very early stages [2].

Figure 1. Custom design metal heating block for in situ chemistry measurements with magnetic hotplate stirrer (left); ODISC furnace with quartz tube inside and magnetic stirrer below (middle); ODISC furnace with metal autoclave inside and magnetic stirrer below (right).

For more demanding in situ synthesis – at temperatures above 100^oC or in metal autoclaves – the custom designed furnace ODISC was developed on the beamline I12 [3]. The furnace is very versatile with integrated heating, stirring, and precise sample centring and it can be used for a wide range of in situ experiments on the beamline. On the beamline I12, the furnace ODISC can be used in two configurations: 1) in situ measurements of reaction kinetic during solvothermal synthesis experiments, which performed at temperatures below boiling temperature of the solvent. In this case simple quartz tubes are used as a container during large-scale in situ synthesis [4]. 2) in situ measurements of reaction kinetic during hydrothermal synthesis, which should be performed in metal autoclaves. Despite measurements during the crystallization were performed in the metal autoclave, the data quality recorded on the beamline I12 allowed the refinement of the diffraction data and subsequent analysis of crystallization kinetic [5].The references should be in Heading 4 style (Times New Roman 9 pt, shortcut CTRL + NUM 4) and listed immediately at the end of the text without a heading.

[1] Drakopoulos M., Connolley T., Reinhard C., Atwood R., Magdysyuk O., Vo N., Hart M., Connor L., Humphreys B., Howell G., Davies S., Hill T., Wilkin G., Pedersen U., Foster A., De Maio N., Basham M., Yuan F., Wanelik K. J. (2015). Synchrotron Rad. 22, 828.

[2] Yeung H.H-M., Sapnik A.F., Massingberd-Mundy F., Gaultois M.W., Wu Y., Fraser D.A.X., Henke S., Pallach R., Heidenreich N., Magdysyuk O.V., Vo N.T., Goodwin A.L. (2019). Angew. Chem., Int. Ed., 58, 566.

[3] Moorhouse S.J., Vranješ N., Jupe A., Drakopoulos M., O’Hare D. (2012). Rev. Sci. Instr. 83, 084101

[4] Cliffe M.J., Castillo-Martínez E., Wu Y., Lee J., Forse A.C., Firth F.C.N., Moghadam P.Z., Fairen-Jimenez D., Gaultois M.W., Hill J. A., Magdysyuk O.V., Slater B., Goodwin A.L., Grey C.P. (2017). J. Am. Chem. Soc. 139, 5397.

[5] Cook D.S., Wu Y., Lienau K., Moré R., Kashtiban R.J., Magdysyuk O.V., Patzke G.R., Walton R.I. (2017). Chem. Mater. 29, 5053–2057.

The activation of B-H bonds in σ-borane complexes is of interest not only due to their applications in catalysis (hydroborations, borylations), but because of the ambiguity of σ-borane coordination modes, which can be challenging to formerly define.^[1] Because σ-borane complexes are intermediates to B-H activation, they can be difficult to study due to the transience of the highly reactive species.

The σ-borane complexes [Rh(PONOP)(ɳ²-HBR)][BAr^F₄], (PONOP = 2,6-Bis(di-tert-butyl-phosphinito)pyridine; Ar^F = 3,5‑Bis(trifluoromethyl)phenyl; HBR = HBcat: 1; HBR = HBpin: 2) have been synthesised in good yields and have been established to undergo oxidative addition (OA) in solution at modest temperatures (< 75 °C). However, the OA products were unstable in solution, preventing their full characterisation using traditional solution-based methods. A single crystal high-pressure study of 1 was undertaken up to pressures of 25.8 kbar. An isomorphous phase transition was observed between the pressures of 4.8 and 8.8 kbar, which was accompanied by several geometrical rearrangements of the HBcat ligand with respect to the remainder of coordination complex. Most notably, the decrease in the N-Rh-B bond angle of ca. 6 ° across the phase transition suggests an increased overlap between the metal d orbital and the ‘empty’ boron orbital, indicating a stronger interaction between the metal centre and the σ-borane ligand. ^[2]

We aim to further the understanding of B-H bond activation by studying σ-borane complexes using high-pressure X-ray diffraction (HP-XRD) as the principal analytical tool. Precise structural determination and analysis of a systematic series of σ-borane complexes will ultimately allow for better modelling of their reactive transition states in associated catalytic cycles, ultimately enabling better targeted design of industrially relevant catalysts.

[1] Hebden, T. J.; Denney, M. C.; Pons, V.; Piccoli, P. M. B.; Koetzle, T. F.; Schultz, A. J.; Kaminsky, W.; Goldberg, K. I.; Heinekey, D. M. (2008) J. Am. Chem. Soc. 130, 10812–10820.

[2] Marder, T. B.; Lin, Z., Contemporary Metal Boron Chemistry I. Springer-Verlag: Berlin Heidelberg, 2008; Vol. 130, p 125-127.

Keywords: organometallic chemistry; B-H bond activation; pincer complexes; high-pressure crystallography

Alex Longcake acknowledges the Royal Society for a PhD studentship (RGFEA180160) and Diamond Light Source for time on Beamline I19 under proposal CY26847.

The development of carbon-neutral energy-generation is critical to combatting climate change. One such technology is the development of next-generation ion conductors for solid-oxide fuel cells (SOFCs). SOFCs offer a much more efficient method to extract energy from hydrogen or hydrocarbon fuels than current combustion engines due to their one-step chemical process. However, a bottleneck to the large-scale uptake of SOFCs is the poor performance of the conducting electrolytes that separate the anode from the cathode. Various lanthanoid fergusonite structures (LnBO₄) have recently been proposed as solid electrolyte candidates in solid-oxide fuel cells, with increased high-temperature ionic conductivity being measured in chemically doped lanthanum orthoniobates (LaNbO₄) [1]. However, a phase transition from I2/a to I4₁/a within the operational temperature of SOFCs makes these structures non-ideal.

To understand the effects of chemical doping on the structure and electrochemical properties of these fergusonite structures, several complex fergusonites have been investigated [2-3]. Of interest is the substitution of Nb^V for Ta^V on the B-site, which has shown a decrease in the unit cell volume of the structure [4]. This is particularly remarkable, given the two metal cations have the same ionic radius and Ta has an extra 5d valence shell compared to the 4d shell of Nb. Such substitution has further shown to increase the I2/a to I4₁/a first-order phase transition temperature, highlighting the potential of the properties of these structures to be specifically ‘tailored’ to be used for SOFCs.

Various solid-solution series of Ln(Nb_1-xTa_x)O₄ (Ln = La-Lu) have been synthesised using conventional solid-state methods. Synchrotron X-ray and neutron powder diffraction methods have been used to investigate their structures, focusing on changes in both their unit cell volumes and the temperature of the I2/a to I4₁/a phase transitions. Whilst the fergusonite structure is a monoclinic structure derived of the tetragonal scheelite aristotype, it’s structure is based on BO₆ polyhedra as opposed to BO₄ scheelite polyhedra. These studies have revealed several anomalies, revealing that different structures can be isolated by controlling the size of the Ln ion and synthetic conditions, and that the volume of the BO₆ polyhedra and length of the B–O bonds change depending on its surrounding Ln ion. This data surprisingly implies that the AO₈ polyhedra act as a rigid framework in which the BO₆ polyhedra respond. The experimental data has been further reinforced by ground state energy calculations performed using density functional theory. This is a landmark accomplishment that has not been previously used in similarly studied structures. These insights can be used in the development and engineering of novel and advanced electrolyte materials for SOFCs.

[1] - Cao, Y.; Duan, N.; Yan, D.; Chi, B.; Pu, J.; Jian, L.; Enhanced Electrical Conductivity of LaNbO₄ by A-Site Substitution. Int. J. Hydrogen Energy, 2016, 41 (45), 20633-20639.

[2] - Arulnesan, S. W.; Kayser, P.; Kimpton, J. A.; Kennedy, B. J.; Studies of the Fergusonite to Scheelite Phase Transition in LnNbO₄ Orthoniobates. J. Solid State Chem., 2019, 277, 229-239.

[3] - Ivanova, M.; Ricote, S.; Meulenberg, W. A.; Haugsrud, R.; Ziegner, M.; Effects of A- and B-Site (Co-)Acceptor Doping on the Structure and Proton Conductivity of LaNbO₄. Solid State Ionics, 2012, 213, 45-52.

[4] – Mullens, B. G.; Avdeev, M.; Brand, H. E. A.; Vaitheeswaran, G.; Kennedy, B. J.; Insights into the Structural Variations in SmNb_1-x­Ta_xO₄ and HoNb_1-xO₄ Combined Experimental and Computational Studies. Under Revision for Dalton Transactions.

Studies of "dark matter" is an important fundamental branch of modern cosmology and theoretical physics. Cryogenic scintillation detectors based on single crystals of tungstates (ZnWO₄, CaWO₄, Na₂W₂O₇) can be used to register "dark matter"; they register extremely rare signals of interaction of Weakly Interacting Massive Particles (WIMP) with the nuclei of the detector material [1].

The important requirements to scintillation materials for the search and registration of such rare events are luminescence, light yield, energy resolution, high level of radiation purity. Necessary radiation purity level and optical quality of scintillators require the development of special technologies for deep purification of starting materials and new approaches to crystal growth under conditions of low temperature gradients, the production of scintillation elements with a high utilization rate of the costly starting material. Scintillation bolometers based on Na₂W₂O₇ must also be of high mechanical strength for their practical significance since bolometric elements of specified form will have to be cut from the crystals. To improve the mechanical and optical characteristics, charge with chromium Cr⁺³ and cerium Ce⁺⁴ doping was prepared, doped Na₂W₂O₇ crystals were grown and their luminescent properties were investigated [2].

Na₂W₂O₇ crystals were grown from melt by low-thermal-gradient Czochralski technique (LTG Cz) developed at NIIC SB RAS (Novosibirsk, Russia). Major difference from conventional Czochralski technique is in temperature gradients reduced by two orders of magnitude, below 1 K/cm. Main advantages of LTG Cz are reduced thermoelastic stresses in growing crystals so that they don’t influence crystal quality, and suppression of melt components decomposition and volatilization. By LTG Cz many scintillating crystals of record size and optical quality were obtained, such as BGO, CdWO₄ and many other [3].

As precursors, Na₂CO₃, WO₃, CeO₂, TiO₂ and Cr₂O₃ powders were used. Initial charge for crystal growth was prepared by solid-state synthesis at 400 °C in muffle furnace according to the reaction:

Na₂CO₃ + 2WO₃ → Na₂W₂O₇ + CO₂ ↑

Completeness of synthesis was controlled by weight change due to CO₂ volatilization. Crystallization rate was set at 1.5 mm/h, rotation velocity at 10 rev/min. Diameter of grown Na₂W₂O₇ crystals was 30 mm, length up to 70 mm and 40 mm for pure and doped ones, correspondingly.

[1] Indra, Raj, Kim, H.J., Lee, H.S., Kim, Y.D., Lee, M.H., Grigorieva, V.D., Shlegel, V.N. (2018) Eur. Phys. J. C, 78, 973. [2] Ryadun, A.A., Rakhmanova, M.I., Grigorieva, V.D. (2020) Optical Materials, 99, 109537. [3] Shlegel, V.N., Borovlev, Yu.A, Grigoriev, D.N, Grigorieva, V.D. et al. (2017) JINST, 12, C08011.

Keywords: Na₂W₂O₇; Czochralski technique; scintillators; elementary particles; luminescence

This work was supported by Russian Foundation for Basic Research (grant No. 20-43-543015).

Correlation between structural studies and third order NLO properties

of three new semi-organic compounds

R. Benali-Cherif R¹, R. Takouachet ¹, E-E Bendeif², N. Benali-Cherif R³

¹Abbes Laghrour Khenchela University. Algeria, ² Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036). France, ³ Houari Boumédiène (USTHB) and Member of Algerian Academy of Sciences and Technology (AAST) Algiers. Algeria Algeria

The study of semi-organic compounds has been of growing interest for a few years. In addition to their fundamental interest in the nature of the bonds occurring between inorganic anions and organic cations, these compounds also have remarkable physico-chemical and optical properties. Recently, the variety of semi-organic hybrid crystals has been developed for NLO applications. The combination of organic compounds, especially amino acids with mineral acids, gives rise to new hybrid crystals with strong NLO properties.Semi-organic compounds play an important role in cell metabolism; they intervene in transfer of energy because of their richness in hydrogen bonds. Inter-ionic interactions through the hydrogen bridges present in this type of semi-organic compounds can serve as mimes explaining some bio-inorganic mechanisms.

Measurement of nonlinear third order electrical susceptibilities was performed for three new compounds (Table 1) by the Third Harmonic Generation (THG) technique. Figure 1 shows the intensity of the THG signal as a function of the angle of incidence, it exhibits the same behavior as the silica.

Table 01. Experimental values of nonlinear susceptibility of the third order.

The third order nonlinear electrical susceptibility values of studied compounds are stronger than that of silica (reference material). The largest value is observed for the first compound, = 9,63×10^-21 m²/V² (Table 1) due to the increase in charge transfer and the large number of hydrogen bonding which increases the dipole moment of the compound .

Figure 1. Intensity of the third harmonic for the three samples

These optical measurements revealed different optical behaviors of the three compounds studied. It is therefore very interesting to analyze and discuss the different structural factors correlated with these interesting physical properties. Several structural parameters affect the physical and optical properties of these materials such as: atomic arrangement, intra- and intermolecular interactions, crystal symmetry and electron density distribution.

Keywords: semi-organic compounds - NLO properties - THG technique

[1] Publication of a book on May 05, 2017 entitled “Corrélations structures propriétés ONL de 3 nouveaux composés hybrides »in the “Éditions Universitaires Européennes »

Materials family of A₃B’₂B’’O₉ (A = alkaline–earth metal ions with valence +2, B’ and B’’= transition metal ions with valences +3 and +6 respectively) were subjected to extensive studies, and have attracted significant interest owing to their physical properties and technological applications. The discovery of colossal magnetoresistance (CMR) in the ordered A₂B’B’’O₆ double perovskite oxides has given rise to many recent research [1–3].

Polycrystalline samples of the series of triple perovskites Sr_3−xPb_xFe₂TeO₉ (0 ≤ x ≤ 2.25) were synthesized using solid state reaction [4]. These materials have been studied by a combination of XRPD, Mössbauer spectrometry, Raman and UV–Vis spectroscopies. The crystal structures were resolved by the Rietveld refinement method, and revealed that this Sr_3−xPb_xFe₂TeO₉ (0 ≤ x ≤ 2.25) system shows one space group change from tetragonal I4/m (0 ≤ x ≤ 1) to another tetragonal form I4/mmm (1.25 ≤ x ≤ 1.88) and a second transition to hexagonal R-3m (2.08 ≤ x ≤ 2.25). The valence state of iron in the Fe site was determined to be Fe(III) by Mössbauer spectrometry, which also revealed two sites in a concordance with the XRPD measurements. ⁵⁷Fe Mössbauer spectra measurements show paramagnetic and magnetic ordering behaviors. The observed Raman spectra as a function of composition show obvious changes on the positions (wavenumbers), the FWHM and the intensities of the modes confirming the phase transformations observed by the XRPD results. These structural transitions led to a distinct change in the optical band gap energy, varying from 2.14 to 1.85 eV.

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