High-quality zirconium vanadate samples for negative thermal expansion analysis
Janine George 1 ,Aistė Miliūtė 2 , Björn Mieller 1 , Tomasz M. Stawski 1 1 Bundesanstalt für Materialforschung und -prüfung, Berlin, Germany 2 Friedrich-Schiller-Universität Jena, Germany * aiste.miliute@bam.de,
Zirconium vanadate (ZrV 2 O 7 ) is a well-known negative thermal expansion (NTE) material which exhibits significant isotropic contraction over a broad temperature range (~150 ° C < T < 800 ° C). The linear thermal expansion coefficient of ZrV 2 O 7 is −7.1×10 -6 K -1 [1]. Therefore, it can be used to create composites with controllable expansion coefficients and prevent destruction by thermal shock [2]. Material characterization, leading to application, requires pure, homogenous samples of high crystallinity via a reliable synthesis route. While there is a selection of described syntheses in the literature, it still needs to be addressed which synthesis route leads to truly pure and homogenous samples. Here, we study the influence of the synthesis methods (solid-state, sol-gel, solvothermal) and their parameters on the sample's purity, crystallinity, and homogeneity. The reproducibility of results and data obtained with scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry, and thermogravimetric analysis (DSC/TGA) were analyzed extensively. The sol-gel method proves superior to the solid-state method and produces higher-quality samples over varying parameters. Sample purity also plays an important role in NTE micro and macro-scale characterizations that explain the impact of porosity versus structural changes. Moreover, we implement ab-initio -based vibrational computations with partially treated anharmonicity (quasi- harmonic approximation [3], temperature-dependent effective harmonic potentials [4]) in combination with experimental methods to follow and rationalize the negative thermal expansion in this material, including the influence of the local structure disorder, microstructure, and defects. Khosrovani et al. [5] and Korthuis et al. [6], in a series of diffraction experiments, attributed the thermal contraction of ZrV 2 O 7 to the transverse thermal motion of oxygen atoms in V-O-V linkages. In addition to previous explanations, we hypothesize that local disorder develops in ZrV 2 O 7 crystals during heating. We are working on the experimental ZrV 2 O 7 development and discuss difficulties one might face in the process as well as high-quality sample significance in further investigation. The obtained samples are currently used in the ongoing research of structure analysis and the negative thermal expansion mechanism. References 1. W. Wei et al. , Applied Physics Letters , vol. 116, p. 181902, May 2020, doi: 10.1063/1.5143691. 2. Y. Yamamura, A. Horikoshi, S. Yasuzuka, H. Saitoh, and K. Saito, Dalton Trans. , vol. 40, no. 10, pp. 2242–2248, Feb. 2011, doi: 10.1039/C0DT01087A. 3. R. P. Stoffel, C. Wessel, M.-W. Lumey, and R. Dronskowski, Angewandte Chemie International Edition , vol. 49, no. 31, pp. 5242–5266, Jun. 2010, doi: 10.1002/anie.200906780. 4. O. Hellman, P. Steneteg, I. A. Abrikosov, and S. I. Simak, Phys. Rev. B , vol. 87, no. 10, p. 104111, Mar. 2013, doi: 10.1103/ PhysRevB.87.104111. 5. N. Khosrovani, A. Sleight, and T. Vogt, 1997, doi: 10.1006/JSSC.1997.7474. 6. V. Korthuis, N. Khosrovani, A. W. Sleight, N. Roberts, R. Dupree, and W. W. Jr. Warren, Chem. Mater. , vol. 7, no. 2, pp. 412–417, Feb. 1995, doi: 10.1021/cm00050a028.
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