Thermodynamics of dual-phase compositionally complex ceramics: A case study of ultrahigh-entropy fluorite-bixbyite refractory oxides. Issue 5 (May 2023)

• Record Type: Journal Article
• Authors: Vega, Heidy; Qin, Mingde; Luo, Jian
• Is Part Of: Journal of the European Ceramic Society. Volume 43:Issue 5(2023)
• Page Start: 2104
• Page End: 2114
• Publication Date: 2023-05
• Subjects: High-entropy ceramics (HECs) -- Compositionally complex ceramics (CCCs) -- Dual-phase compositionally complex ceramics (DP-CCCs) -- Compositionally complex refractory oxides (CCROs) -- Thermodynamics; 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.2022.12.033
• Languages: English
• ISSNs: 0955-2219

Abstract

Abstract: A set of 8-, 10-, 12-, and 14-component compositionally complex refractory oxides (CCROs, containing Nb, Ta, Ti, Zr, Hf, Ce, Yb, Tm, Er, Ho, Y, Dy, Tb, and Gd) have been successfully fabricated. In addition to five single-phase high- and ultrahigh-entropy CCROs in either bixbyite or defect fluorite structure, nine dual-phase CCROs have been made with co-existing fluorite and bixbyite phases (in a thermodynamic equilibrium each other), representing a new class of dual-phase compositionally complex ceramics (DP-CCCs). A thermodynamic relation dictating the dual-phase equilibria is discovered, where the ratio of the atomic fractions in the two equilibrium phases remains roughly a constant. Interestingly, this ratio for eight different trivalent rare-earth cations linearly depends on the ionic radius ( r i ). A further analysis showed that the differential enthalpy of solution in the bixbyite versus fluorite phase approximately follows Δ H i (eV) = –0.80·( r i – 1.06 Å). Such thermodynamic relations are important for designing DP-CCCs. Highlights: 8- to 14-component compositionally complex refractory oxides (CCROs) are fabricated. A new class of ultrahigh-entropy fluorite-bixbyite dual-phase CCROs are reported. A simple thermodynamic relation dictating the dual-phase equilibria is discovered. For rare-earth cations, differential enthalpy of solution linearly depends on the ion radius. Thermodynamics is useful for designing dual-phase compositionally complex ceramics.