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 tra...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:~2.7kB per cation or higher on one sublattice in most cases).Notably,(15RE_(1/15))(Nb_(1/2)Ta_(1/2))O_(4) possess a single monoclinic fergusonite(C2/c)phase,and(15RE_(1/15))_(3)(Nb_(1/2)Ta_(1/2))_(1)O_(7) form a single orthorhombic(C222_(1))weberite phase,where 15RE_(1/15) represents Sc_(1/15)Y_(1/15)La_(1/15)Pr_(1/15)Nd_(1/15)Sm_(1/15)Eu_(1/15)Gd_(1/15)Tb_(1/15)Dy_(1/15)Ho_(1/15)Er_(1/15)Tm_(1/15) Yb_(1/15)Lu_(1/15).Moreover,a series of eight(15RE_(1/15))_(2+x)(Ti_(1/4)Zr_(1/4)Ce_(1/4)Hf_(1/4))_(2−2x)(Nb_(1/2)Ta_(1/2))_(x)O_(7) 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.展开更多
Over the past decade,the field of high-entropy ceramics(HECs)has expanded rapidly to encompass a broad range of oxides,borides,silicides,and other ceramic solid solutions.In 2020,we proposed extending HECs to composit...Over the past decade,the field of high-entropy ceramics(HECs)has expanded rapidly to encompass a broad range of oxides,borides,silicides,and other ceramic solid solutions.In 2020,we proposed extending HECs to compositionally complex ceramics(CCCs),where non-equimolar compositions and the presence of long-or short-range order,although reducing configurational entropy,create new op-portunities to tailor and enhance properties,often surpassing those of higher-entropy counterparts.Along these lines,several fundamental scientific questions arise.Is the entropy in HECs truly high?Is maximizing entropy always desirable?In this perspective article,I revisit key concepts and terminologies and highlight emerging directions,including dual-phase CCCs,ultrahigh-entropy phases,and novel processing routes such as ultrafast reactive sintering.I propose that exploring compositional complexity across vast non-equimolar spaces,together with exploiting correlated disorder(coupled chemical and structural short-range order),represents a transformative strategy for designing ceramics with superior performance.展开更多
基金The work is supported by the National Science Foundation(NSF)in the Ceramics program via Grant No.DMR2026193This work utilized the shared facilities at the San Diego Nanotechnology Infrastructure of UCSD,a member of the National Nanotechnology Coordinated Infrastructure(supported by the NSF ECCS-1542148)the Irvine Materials Research Institute(partially supported by NSF DMR-2011967 through UCI CCAM).
文摘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:~2.7kB per cation or higher on one sublattice in most cases).Notably,(15RE_(1/15))(Nb_(1/2)Ta_(1/2))O_(4) possess a single monoclinic fergusonite(C2/c)phase,and(15RE_(1/15))_(3)(Nb_(1/2)Ta_(1/2))_(1)O_(7) form a single orthorhombic(C222_(1))weberite phase,where 15RE_(1/15) represents Sc_(1/15)Y_(1/15)La_(1/15)Pr_(1/15)Nd_(1/15)Sm_(1/15)Eu_(1/15)Gd_(1/15)Tb_(1/15)Dy_(1/15)Ho_(1/15)Er_(1/15)Tm_(1/15) Yb_(1/15)Lu_(1/15).Moreover,a series of eight(15RE_(1/15))_(2+x)(Ti_(1/4)Zr_(1/4)Ce_(1/4)Hf_(1/4))_(2−2x)(Nb_(1/2)Ta_(1/2))_(x)O_(7) 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.
文摘Over the past decade,the field of high-entropy ceramics(HECs)has expanded rapidly to encompass a broad range of oxides,borides,silicides,and other ceramic solid solutions.In 2020,we proposed extending HECs to compositionally complex ceramics(CCCs),where non-equimolar compositions and the presence of long-or short-range order,although reducing configurational entropy,create new op-portunities to tailor and enhance properties,often surpassing those of higher-entropy counterparts.Along these lines,several fundamental scientific questions arise.Is the entropy in HECs truly high?Is maximizing entropy always desirable?In this perspective article,I revisit key concepts and terminologies and highlight emerging directions,including dual-phase CCCs,ultrahigh-entropy phases,and novel processing routes such as ultrafast reactive sintering.I propose that exploring compositional complexity across vast non-equimolar spaces,together with exploiting correlated disorder(coupled chemical and structural short-range order),represents a transformative strategy for designing ceramics with superior performance.
