From high-entropy ceramics to compositionally-complex ceramics: A case study of fluorite oxides. Issue 5 (May 2020)

• Record Type: Journal Article
• Authors: Wright, Andrew J.; Wang, Qingyang; Huang, Chuying; Nieto, Andy; Chen, Renkun; Luo, Jian
• Is Part Of: Journal of the European Ceramic Society. Volume 40:Issue 5(2020)
• Page Start: 2120
• Page End: 2129
• Publication Date: 2020-05
• Subjects: High-Entropy ceramics (HECs) -- Compositionally-Complex ceramics (CCCs) -- Multi-Principal cation ceramics (MPCCs) -- Thermal conductivity -- Thermal barrier coatings; Ceramic materials -- Periodicals; Composite materials -- Periodicals; Matériaux céramiques -- Périodiques; Composites -- Périodiques; Ceramic materials; Composite materials; Periodicals; Electronic journals; 666.05
• DOI: 10.1016/j.jeurceramsoc.2020.01.015
• Languages: English
• ISSNs: 0955-2219

Abstract

Highlights: Nine compositionally-complex fluorite oxides (CCFOs) are made and investigated. CCFOs exhibit reduced thermal conductivity and increased cubic phase stability. Lower thermal conductivity is achieved in medium-entropy non-equimolar CCFOs. High modulus and hardness retain in CCFOs with reduced thermal conductivity. Non-equimolar CCFOs exhibit amorphous-like T-dependent thermal conductivity. Abstract: Using fluorite oxides as an example, this study broadens high-entropy ceramics (HECs) to compositionally-complex ceramics (CCCs) or multi-principal cation ceramics (MPCCs) to include medium-entropy and/or non-equimolar compositions. Nine compositions of compositionally-complex fluorite oxides (CCFOs) with the general formula of (Hf1/3 Zr1/3 Ce1/3 )1- x (Y1/2 X 1/2 ) x O2-δ ( X = Yb, Ca, and Gd; x = 0.4, 0.148, and 0.058) are fabricated. The phase stability, mechanical properties, and thermal conductivities are measured. Compared with yttria-stabilized zirconia, these CCFOs exhibit increased cubic phase stability and reduced thermal conductivity, while retaining high Young's modulus (∼210 GPa) and nanohardness (∼18 GPa). Moreover, the temperature-dependent thermal conductivity in the non-equimolar CCFOs shows an amorphous-like behavior. In comparison with their equimolar high-entropy counterparts, the medium-entropy non-equimolar CCFOs exhibit even lower thermal conductivity ( k ) while maintaining high modulus ( E ), thereby achieving higher E / k ratios. These results suggest a new direction to achieve thermally-insulative yet stiff CCCs (MPCCs) via exploring non-equimolar and/or medium-entropy compositions.