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

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.

Exploring negative thermal expansion materials with bulk framework structures and their relevant scaling relationships through multi-step machine learning

“…The training data contains nearly 200 NTE materials from the published literature 16–127 and about 230 positive thermal expansion (PTE) data with the same structures or elements as NTE materials. To improve the reliability of the prediction capability, we employed the three-step ML method with data augmentation and cross-validation.…”

Low-Temperature Rapid Sintering of Dense Cubic Phase ZrW2−xMoxO8 Ceramics by Spark Plasma Sintering and Evaluation of Its Thermal Properties

“…Thus, the investigation of alternative low-temperature liquid-phase methods is rather mandatory. It has been reported that ZrW 2 O 8 powders can be prepared by dehydrating its hydrate precursor ZrW 2 O 7 (OH) 2 •2H 2 O, which can be obtained using liquid-phase methods such as solgel [1,2,[29][30][31], hydrothermal [3,5,[32][33][34][35][36] and co-precipitation [35]. Kanamori et.…”

Ultra‐low thermal expansion behavior of spark plasma sintered Sn‐doped ZrMo2O8

“…Previous research on SPS of ZrW 2 O 8 composites demonstrates the success of the method in achieving near-theoretical densities. [15][16][17] Wei et al 18 discussed how W can be partially substituted with Mo to overcome sinterability issues that arises due to the low-temperature phase transition in ZrW 2 O 8 . While these studies suggest solutions to address the discontinuity in the thermal expansion behavior of ZrW 2 O 8 , there are no prior reports on SPS of ZrMo 2 O 8 to the best of our knowledge.…”