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.

Mingde QIN;Heidy VEGA;Dawei ZHANG;Sarath ADAPA;Andrew J.WRIGHT;Renkun CHEN;Jian LUO

Department of Nano Engineering,University of California San Diego,La Jolla 92093,USA;Department of Chemistry and Biochemistry,University of California San Diego,La Jolla 92093,USA;Program of Materials Science and Engineering,University of California San Diego,La Jolla 92093,USA;Department of Mechanical and Aerospace Engineering,University of California San Diego,La Jolla 92093,USA

先进陶瓷（英文版）

[1]Mingde QIN;Heidy VEGA;Dawei ZHANG;Sarath ADAPA;Andrew J.WRIGHT;Renkun CHEN;Jian LUO-.21-Component compositionally complex ceramics:Discovery of ultrahigh-entropy weberite and fergusonite phases and a pyrochlore-weberite transition)[J].先进陶瓷（英文版）,2022(04):641-655

weberite,fergusonite,15RE1,2Ta1,15Y1,15La1,15Pr1,15Nd1,15Sm1,15Eu1,15Gd1,15Tb1,15Dy1,1sHo1,15Er1,15Tm1,Yb1,15Lu1,2+x,4Zr1,4Ce1,4Hf1,xO7,CCCs

Component,compositionally,ceramics,Discovery,ultrahigh,entropy,phases,pyrochlore,transition,Two,new,HECs,structures,along,unexpected,formation,ordered,compositions,abrupt,are,discovered,component,system,While,Gibbs,rule,allows,equilibrium,out,examined,possess,single,ideal,configurational,entropies,kB,cation,higher,sublattice,most,cases,Notably,Nb1,O4,monoclinic,1O7,orthorhombic,C2221,where,represents,Sc1,Moreover,series,eight,Ti1,2x,specimens,exhibit,occurs,within,This,cubic,does,not,change,temperature,dependent,thermal,conductivity,appreciably,amorphous,limit,may,have,already,been,achieved,oxides,These,discoveries,expand,diversity,complexity,towards,many

0.400745