21-Component compositionally complex ceramics:Discovery of ultrahigh-entropy weberite and fergusonite phases and a pyrochlore-weberite transition

• 作者: Mingde QIN Heidy VEGA Dawei ZHANG Sarath ADAPA Andrew J.WRIGHT Renkun CHEN Jian LUO
• 来源期刊: 先进陶瓷（英文版）
• 年，卷（期）: 2022,（4）
• 所属期刊栏目: Research Article
• 页码范围: 641-655
• 页数: 15页
• 语种: 英文

摘要

Two new high-entropy ceramics(HECs)in the weberite and fergusonite structures,along with the unexpected formation of ordered pyrochlore phases with ultrahigh-entropy compositions and an abrupt pyrochlore-weberite transition,are discovered in a 21-component oxide system.While the Gibbs phase rule allows 21 equilibrium phases,9 out of the 13 compositions examined possess single HEC phases(with ultrahigh ideal configurational entropies:～2.7 kB per cation or higher on one sublattice in most cases).Notably,(15RE1/15)(Nb1/2Ta1/2)O4 possess a single monoclinic fergusonite(C2/c)phase,and(15RE1/15)3(Nb1/2Ta1/2)1O7 form a single orthorhombic(C2221)weberite phase,where 15RE1/15 represents Sc1/15Y1/15La1/15Pr1/15Nd1/15Sm1/15Eu1/15Gd1/15Tb1/15Dy1/1sHo1/15Er1/15Tm1/15 Yb1/15Lu1/15.Moreover,a series of eight(15RE1/15)2+x(Ti1/4Zr1/4Ce1/4Hf1/4)2-2x(Nb1/2Ta1/2)xO7 specimens all exhibit single phases,where a pyrochlore-weberite transition occurs within 0.75＜x＜0.8125.This cubic-to-orthorhombic transition does not change the temperature-dependent thermal conductivity appreciably,as the amorphous limit may have already been achieved in the ultrahigh-entropy 21-component oxides.These discoveries expand the diversity and complexity of HECs,towards many-component compositionally complex ceramics(CCCs)and ultrahigh-entropy ceramics.