Composite Polycaprolactone (PCL) materials with different amounts of clays were prepared employing two mixing techniques: a two screw extruder and an intensive mixer (Brabeder type) followed by compression moulding in a hydraulic press. Simultaneous Small and Wide angle X ray Scattering (SAXS/WAXS) measurements were done in order to evaluate the structural characteristics and preferential orientation of the composites. On the one hand, the effect of the clay inclusion in the PCL lamellar structure was evaluated, and moreover, the clay interlayer distance was compared between composites.

Upon the modification of the clays with Benzolconion Chloride (CBK), an anisotropic effect becomes noticeable in the 2D SAXS patterns recorded on Pilatus (Dectris) detector (Fig. 1), when the sample is analysed with the plane of the film parallel to the direction of the incident beam.

For all cases, there were no changes in the PCL structure due to clay inclusion. For modified clays, in two of the three analysed systems, the clay interlayer characteristic peak shifts towards lower angles, corresponding to an increment in the distance from 1.3 to 1.7nm. And in all cases, a new peak appears at lower angles for the modified samples, attributed to an interlayer spacing distance of the nano sized clays of 2.7 - 2.9 nm, only for patterns of the samples placed parallel to the direction of the incident beam. Different loads yield different intensities in the most intense region, proportional to the amount of load.

It was shown that the orientation is dependent on the synthesis procedure and also on the clay characteristics. These results can be correlated with the mechanical behaviour of the developed films which is a relevant parameter for the application of material on food packaging.

X-ray absorption fine structure (XAFS) spectroscopy is one of the most widely used synchrotron radiation based methods to study local structures and electronic states of elements. Chemical reactions have been observed by in situ XAFS methods. However, XAFS is fundamentally bulk sensitive, and is difficult to apply to study surface phenomena or reactions.
We have developed a surface sensitive x-ray spectroscopy, which is named Total REflection
X-ray Spectroscopy (TREXS), to study surfaces in nanometer scale. Reflection spectra are recorded in total reflection conditions, and the surface sensitivity of about 2-3 nm is realized. In brief, TREXS enables us to obtain two kinds of information, which essentially correspond to usual XANES and EXAFS. Near edge regions of total reflection spectra are analyzed to discuss electronic structures and chemical states, and surface reactions can be monitored by tracking the changes. In addition, total reflection spectra are transformed to XAFS spectra through Kramers-Kronig relations, and regular EXAFS analysis methods can be applied.
It was reported that a reduction reaction of surface NiO layer to Ni metal with
the surface sensitivity of ~2-3 nm[1,2].
In this contribution, we will present surface chemical reactions studied by in situ TREXS, development of multi-modal surface research equipment by combining TREXS with IRRAS (Infrared Reflection Absorption Spectroscopy), and an ongoing plan to involve also scattering techniques in the TREXS experimental equipment.
This will lead to develop an experimental setup to study surfaces in nanometer scale by spectroscopy (TREXS) and scattering including diffraction at the same time under reaction conditions.
References
[1] H. Abe, et al., Jpn. J. Appl. Phys. 55, 062401 (2016).
[2] H. Abe, et al., Chem. Rec. 19, 1457 (2019).

Zirconium solutions have long been used as raw precursors in a range of applications to produce a diverse range of materials and products, including ZrO₂ nanoparticles and high temperature ceramics which are widely used as catalysts and sorbents ^[1-3]. It is commonly accepted that the structure of the species in the zirconium solution is influential in the properties, chemical and physical, of any subsequent materials. It is for this reason that it is of critical importance that we fully understand the structure of the species within these solutions, and subsequently use this information to inform and adapt synthetic methods.

There is evidence that Zr(IV), in aqueous solution, has a tendency towards hydrolysis and polymerisation. A tetranuclear species [Zr₄(OH)₈(OH₂)₁₆]⁸⁺ was proposed by Clearfield and Vaughn ^[4]. This species has a square 4 – Zr core held together by 8 hydroxyl bridges with 16 terminal waters. This structure was determined through the use of single crystal X-Ray diffraction (XRD) on solid samples of recrystallised ZrOCl₂·8H₂O solution. Since its discovery in 1956, this structure has widely been regarded as being correct and its tetramer complex considered present in the aqueous phase ^[5]. Unfortunately, any attempts to study this species whilst still in aqueous solutions have been limited due to the lack of long range order in solution species, hence disallowing traditional laboratory crystallographic methods. However, recent developments of total scattering pair distribution function (PDF) have allowed for the study of disordered systems including glasses and, more importantly, liquids. This allows for the characterisation and modelling of solution species through methods similar to those traditionally associated with XRD and Rietveld refinements. Through the use of these methods we have been able to isolate contributions to the PDF pattern from the tetranuclear species, and subsequently refine the ideal solid state model to determine its nature in solution. Recent work by Hu et al. collected PDF data on aqueous zirconyl chloride and, through a method of fitting to Gaussians, confirmed that the general structure, proposed by Clearfield and Vaughn, is indeed present, but no refined inter atomic distances were obtained ^[6]. However through the use of structural refinements we have obtained a model which, whilst similar to the original Clearfield model, has some distortion with respect to bond lengths and angles in the terminal H₂O.

In this work we propose a refined version of the original model, first proposed by Clearfield. We also discuss the use of the Topas suite’s rigid body editor and how, if a starting model is widely considered to be accurate, this offers enough flexibility to refine small differences to get a truly optimal model, with an extremely high level of precision, whilst ensuring that the statistics of the refinement are mathematically believable. The method used to obtain this refinement will be subsequently applied to further aqueous zirconium carboxylates which are yet to have their solution species identified.

[1] Geiculescu, A.C. et al., Sol-Gel Sci. and Tech., 2000. 17(1): p. 25-35. [2] De Keukeleere, K., et al., Inorg. Chem., 2015. 54(7): p. 3469-3476. [3] Feth, M.P., et al., Non-Crystalline Solids, 2005. 351(5): p. 432-443. [4] Clearfield, A. et al., Acta Cryst., 1956. 9(7): p. 555-558. [5] Hennig, C., et al., Inorg. Chem., 2017. 56(5): p. 2473-2480. [6] Hu, Y.-J., et al., American Chem. Soc., 2013. 135(38): p. 14240-14248.

Traditional Li-ion battery electrodes are highly crystalline materials in which the ions are intercalated between atomic layers or channels in the atomic lattice. Such electrodes are typically characterized by retaining their crystallinity for many charge-discharge cycles. However, a number of electrode materials undergo an irreversible loss of crystallinity upon Li-intercalation. Examples of such materials are rutile TiO₂ and orthorhombic V₂O₅, which loses long range order upon intercalation of >0.8 and >2 Li, respectively [1,2]. Very little is presently known about neither the mechanism of such order-disorder phenomena nor about how ion storage occurs in disordered structures in subsequent charge-discharge cycles. This is in spite that such materials represent cheap and effective alternatives to their crystalline counterparts, i.e. recently amorphous V₂O₅ was shown to reversibly store close to double the amount of Na-ions as compared to crystalline V₂O₅ [3].

Herein, we investigate the structural evolution during Li-intercalation and the associated disordering process in nano-rutile TiO₂ by means of combined ex situ and operando synchrotron radiation powder X-ray diffraction and total scattering with pair distribution function (PDF) analysis. We find that, the disorder mechanism entails a reconstructive phase transformation with formation of a distorted α-NaFeO₂ structure. Furthermore, small disordered domains form due to extensive dislocations between the distorted α-NaFeO₂ domains [4].

After amorphization, TiO₂ reversibly stores ~200 mAh/g with ion storage occurring via solid solution reactions with remarkable small volume changes between the end-members. Our results suggest that these materials may hold potential as cheap electrode materials despite the fact that they lose long range order. Also our methodology opens for investigating a wide range of order-disorder phenomena in electrochemically driven phase transitions.

[1] Borghols, W. J. H., Wagemaker, M., Lafont, U., Kelder, E. M. & Mulder, F. M. (2008). Chem. Mater. 20, 2949.

[2] Delmas, C., Cognac-Auradou, H., Cocciantelli, J.M., M6n6tder, M. & Doumerc, J.P. (1994). Solid State Ionics 69, 257.

[3] Uchaker, E., Zheng, Y. Z., Li, S., Candelaria, S. L., Hu, S. & Cao, G. Z. (2014). J. Mater. Chem. A 2, 18208

[4] Christensen, C. K., Balakrishna,A. R., Iversen, B. B., Chiang, Y.-M. & Ravnsbæk, D. B. (2019). Nanoscale 11, 12347.

While the silicon-rich members of the series Cu₂Zn(Ge,Si)Se₄ crystallize in wurtz-kesterite type structure [1], germanium-rich samples adopt a tetrahedral structure of the kesterite type [2] (figure 1). Identification of the silicon site is straightforward from regular X-ray diffraction, as Si⁴⁺ is a light element and has less electrons than the other cations. However, Cu¹⁺, Zn²⁺, and Ge⁴⁺ are all isoelectronic and have very similar form factors. The kesterite type of the cation distribution of Cu₂ZnGeSe₄ has been established by neutron diffraction [2], which can distinguish these elements.

We now applied anomalous X-ray diffraction to this system, using Rietveld refinement and Multiple Edge Anomalous Diffraction (MEAD) [3] with data taken at the K-absorption edges of Cu, Zn, and Ge. These energies are accessible at beamline KMC-2, BESSY II, Berlin [4]. The Si-rich end member Cu₂ZnSiSe₄ has previously shown to be wurtz-kesterite by MEAD [1]. With the correct structure type, the degree of Cu/Zn disorder within the Si-rich region of the series could be determined reliably from multiple-energy Rietveld refinement. For the Ge-rich, tetragonal structures, MEAD was found to be the method of choice. In contrast to previous studies, where Sn⁴⁺ was the M(IV) species in the structure [1], in Cu₂ZnGeSe₄ all cations have very similar scattering power under normal conditions. This results in superstructure peaks (with respect to the cubic ZnS parent structure) that are very weak. For Rietveld analysis this is a drawback, as the optimization will be dominated by the main peaks of the parent structure. In MEAD, however, it increases the effect of the changing scattering power close the absorption edges. As a result, not only are Kesterite and Stannite types clearly distinguishable at the Cu-K edge (figure 2), also the Cu/Zn ordering within the Kesterite structure is clearly detectable and quantifiable at the Zn-K edge.

The degree of Cu/Zn order for the full series could thus be compared to other structural and physical parameters within the Cu₂Zn(Ge,Si)Se₄ solid solution series.

[1] Többens, D. M., Gurieva, G., Niedenzu, S., Schuck, G., Schorr, S. (2020) Acta Cryst. B 76, 1027.

[2] Gurieva, G., Többens, D. M., Valakh, M. Y., Schorr, S. (2016) J. Phys. Chem. Solids 99, 100.

[3] Collins, B. A., Chu, Y. S., He, L., Haskel, D. & Tsui, F. (2015). Phys. Rev. B 92, 224108.

[4] Helmholtz-Zentrum Berlin für Materialien und Energie (2016) J. Large-Scale Res. Facilities 2, A49

The size of nano-ceria particles can be controlled by the amount of time HMT and cerium nitrate are together in solution.[1] The interaction of HMT with cerium nitrate has been studied by in situ Small Angle Scattering (SAXS) and a core structure with a different surface structure is proposed.[2] The Diffuse Reflectance Fourier Transform Spectra (DRIFTS) of this nano-ceria shows significant adsorption of HMT on this surface that transforms to formate and finally carbonate during heating to 425 °C. The combination of PDF and DRIFTS analysis has been used to gain new insights into the structure of this nano-ceria.

A model of HMT interacting with the 111 surfaces of ceria can be made where H bonds from N in HMT can H-bond to OH groups on the ceria surface by aligning the 3-fold axes of the HMT and the 3-fold axis of the 111 surface of ceria (Figure 1). Examination of the G(r) of the Pair Distribution Function (PDF) does not show much evidence for this interaction because the scattering power of the light atoms in the HMT is too weak to show a significant signal when the heavy cerium atoms are present. However, signal enhancing techniques show some support for this model.[3]

Analysis of the PDF of the room temperature data showed that a disordered surface of ceria on a core of ceria gave an improved fit. Additional modeling shows that the disordered surface phase could also be interpreted as ceria with a CeO₈ fragment replaced with an HMT molecule (Figure 2). The refinement with the embedded HMT may not be practical, but a simplified model where one of the 8 cerium atoms has reduced occupancy fits the surface G(r).

The refinement of the temperature dependent PDF data shows the cell dimension variation found in the Rietveld refinement of the powder X-ray data. There is a spike in the cell dimension during the initial ramp which arises from the reduction of the ceria by the oxidation of the HMT or one of its decompaction products. The surface phase has a smaller cell dimension than the core phase and the size and fraction of this shell decreases on heating.

1. Zhang, F., S.W. Chan, J.E. Spanier, E. Apak, Q. Jin, R.D. Robinson, and I.P. Herman,. Appl. Physics Let., 2002. 80(1): p. 127-129.

2. Allen, A.J., V.A. Hackley, P.R. Jemian, J. Ilavsky, J.M. Raitano, and S.W. Chan, J. of Applied Cryst., 2008. 41: p. 918-929.

3. Urakawa, A., T. Burgi, and A. Baiker, Eng. Science, 2008. 63(20): p. 4902-4909.

This work was supported by NSF DMR grant 1206764 and used 28-ID-1 of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory(BNL) under Contract No. DE-SC0012704.

Alumina (Al₂O₃) has many applications, e.g., in cements, substrates of electronic materials, and high-temperature crucibles. Alumina can be classified as an intermediate between glass formers and modifiers, according to Sun [1]. It is impossible to prepare bulk alumina glass by using the melt quenching method and hence electrochemical and sol-gel methods were used to prepare the samples for studying optical properties and the behavior at high temperatures. However, the structure of alumina glass is still largely unknown due to the very limited number of structural studies.

In this study, we performed high-energy X-ray and neutron diffraction measurements on bulk alumina glass prepared by the electrochemical method. To understand diffraction data in detail, we employed a combined classical molecular dynamics-reverse Monte Carlo modelling approach, with coordination number constraints based on NMR data. The formation of OAl₃ triclusters could be confirmed. Detailed topological analyses are in progress.

[1] Sun, K. H. (1947). J. Am. Ceram. Soc. 30, 277.

Vanadium based glasses (vanadate glasses) with a sealing temperature of around 400 °C are now being applied in electronics devices, such as in crystal oscillators and Micro Electro Mechanical Systems (MEMS) as an alternative sealant to the toxic low-melting point glasses containing lead and fluorine. We have developed an Ag₂O-V₂O₅-TeO₂ glass with a sealing temperature of 200-300 °C. However, the structure of the Ag₂O-V₂O₅-TeO₂ glass is still unknown and hence it is necessary to reveal the relationship between the atomistic structure and the property of the vanadate glass.

In this study, we performed high-energy X-ray and neutron diffraction, extended X-ray absorption fine structure (EXAFS), and anomalous X-ray scattering (AXS) [1] measurements on an Ag₂O-V₂O₅-TeO₂ glass to obtain sufficient element specific structural information on constituent atoms. To uncover the glass structure in detail, we constructed a three-dimensional atomistic structure model for Ag₂O-V₂O₅-TeO₂ glass by employing the reverse Monte Carlo [2] technique based on X-ray/neutron diffraction, EXAFS and AXS data. Furthermore, topological analyses were applied to the three-dimensional glass structure model to extract topologies related to the low-melting property.

[1] Saito, M., Park, C., Omote, K., Sugiyama, K., Waseda, Y. (1997). J. Phys. Soc. Jpn. 66, 633.

[2] McGreevy, R. L., Pusztai, L. (1988). Molec. Simul. 1, 359.