High Entropy Rare-Earth Molybdate Ceramics with Broad Operating-Temperature Window and Anti-Hygroscopicity Ability: A Promising Strategy for Negative Thermal Expansion Materials
Wenjuan Zhang, Zhanqiang Li, Zijian Zhou, Fan Yang, Zhaoli Liu, Liyan Xue, Heng Chen, Yong Zheng
Abstract
Negative thermal expansion (NTE) has been an attractive topic in engineering application and functional materials. However, the narrow operating-temperature window and the hygroscopicity have become bottlenecks restricting the NTE behavior. In this work, a design strategy for effectively ameliorating the NTE property, rare-earth based high-entropy (Y 0.2 Yb 0.2 Er 0.2 Tm 0.2 A 0.2 ) 2 Mo 3 O 12 (A = Sc, Gd, Lu) (HE-RE 2 Mo 3 O 12 ) ceramics, is demonstrated for the first time. The as-synthesized HE-RE 2 Mo 3 O 12 ceramics exhibit an orthorhombic crystal structure with a uniform distribution of rare-earth elements. Furthermore, the coefficients of thermal expansion (CTEs) of (Y 0.2 Yb 0.2 Er 0.2 Tm 0.2 Sc 0.2 ) 2 Mo 3 O 12 and (Y 0.2 Yb 0.2 Er 0.2 Tm 0.2 Lu 0.2 ) 2 Mo 3 O 12 ceramics are −4.96 × 10 –6 K –1 and −4.58 × 10 –6 K –1 with high service temperatures (100–800 °C). Fascinatingly, the large ionic radius Gd(III) is incorporated into the orthorhombic (Y 0.2 Yb 0.2 Er 0.2 Tm 0.2 Gd 0.2 ) 2 Mo 3 O 12 ceramic, and a lower negative thermal expansion property (−0.76 × 10 –6 K –1 ) with broad operating-temperature window (100–800 °C) is achieved. Remarkably, the antihygroscopicity ability of the high-entropy specimens is improved, and the water absorption of such ceramics is reduced by 61.4%. Moreover, the improvements of the tunable thermal expansion and antihygroscopicity property of HE-RE 2 Mo 3 O 12 ceramics are ascribed to the lattice distortion effect. The present study provides a promising strategy for the development of NTE functional materials.