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Materials 2018, 11(9), 1582; https://doi.org/10.3390/ma11091582

Low-Temperature Spark Plasma Sintering of ZrW2−xMoxO8 Exhibiting Controllable Negative Thermal Expansion

1
Department of Materials Science and Technology, Tokyo University of Science, Tokyo 1258585, Japan
2
Department of Pure and Applied Chemistry, Tokyo University of Science, Chiba 2788510, Japan
*
Author to whom correspondence should be addressed.
Received: 20 August 2018 / Revised: 28 August 2018 / Accepted: 29 August 2018 / Published: 1 September 2018
(This article belongs to the Section Manufacturing Processes and Systems)
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Abstract

Molybdenum-doped zirconium tungstate (ZrW2−xMoxO8) has been widely studied because of its large isotropic coefficient of negative thermal expansion (NTE). However, low density and poor sinterability limit its production and application. In this study, relative density greater than 90% single-phase ZrW2−xMoxO8 (0.0 ≤ x ≤ 1.0) sintered bodies were fabricated by spark plasma sintering (500–600 °C for 10 min) using ZrW2−xMoxO7(OH)2·2H2O precursor powders as the starting material. High-temperature X-ray diffraction and thermomechanical analysis were used to investigate the change in the order–disorder phase transition temperature of the sintered materials; it gradually dropped from 170 °C at x = 0.0 to 78 °C at x = 0.5, and then to below room temperature at x ≥ 0.7. In addition, all sintered bodies exhibited NTE behavior. The NTE coefficient was controllable by changing the x value as follows: from −7.85 × 10−6 °C−1 (x = 0) to −9.01 × 10−6 °C−1 (x = 0.6) and from −3.22 × 10−6 °C−1 (x = 0) to −2.50 × 10−6 °C−1 (x = 1.0) before and after the phase transition, respectively. Rietveld structure refinement results indicate that the change in the NTE coefficient can be straightforwardly traced to the thermodynamic instability of the terminal oxygen atoms, which only have one coordination. View Full-Text
Keywords: ZrW2−xMoxO8; spark plasma sintering; dense sintered body; thermal analysis; negative thermal expansion ZrW2−xMoxO8; spark plasma sintering; dense sintered body; thermal analysis; negative thermal expansion
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Wei, H.; Hasegawa, M.; Mizutani, S.; Aimi, A.; Fujimoto, K.; Nishio, K. Low-Temperature Spark Plasma Sintering of ZrW2−xMoxO8 Exhibiting Controllable Negative Thermal Expansion. Materials 2018, 11, 1582.

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