Abstract
A powder X-ray diffraction experiment was performed on cubic Zr1-xHfxW2O8 (x=0.25, 0.50 and 0.75) solid solutions from 90 to 560 K. The lattice parameters of Zr1-xHfxW2O8 at 121 K decreased linearly with increasing Hf contents, due to smaller ionic radius of hafnium than that of zirconium. Transition temperatures due to α-β structural phase transition increased with increasing Hf contents, reflecting the decrease of lattice free volume related to the orientation of unshared vertex of WO4. Anomaly in the heat capacity of Zr0.5Hf0.5W2O8 was observed around 450 K which was 9 K lower than that by X-ray diffraction method. Transition entropy of Zr0.5Hf0.5W2O8 was 2.1 J mol-1 K-1, consistent with those of ZrW2O8 and HfW2O8. This consistent entropy supports that Zr1-xHfxW2O8 (x=0-1.0) has the same order-disorder phase transition mechanism.
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Nakajima, N., Yamamura, Y. & Tsuji, T. Phase transition of negative thermal expansion Zr1-xHfxW2O8 solid solutions. Journal of Thermal Analysis and Calorimetry 70, 337–344 (2002). https://doi.org/10.1023/A:1021647717948
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DOI: https://doi.org/10.1023/A:1021647717948