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
Anisotropy and inhomogeneity are ubiquitous in spark plasma sintered thermoelectric devices.However,the origin of inhomogeneity in thermoelectric nanocomposites has rarely been investigated so far.Herein,we systematic...Anisotropy and inhomogeneity are ubiquitous in spark plasma sintered thermoelectric devices.However,the origin of inhomogeneity in thermoelectric nanocomposites has rarely been investigated so far.Herein,we systematically study the impact of inhomogeneity in spark plasma sintered bismuth antimony telluride(BiSbTe)thermoelectric nanocomposites fabricated from solution-synthesized nanoplates.The figure of merit can reach 1.18,which,however,can be overestimated to 1.88 without considering the inhomogeneity.Our study reveals that the inhomogeneity in thermoelectric properties is attributed to the non-uniformity of porosity,textures and elemental distribution from electron backscatter diffraction and energy-dispersive spectroscopy characterizations.This finding suggests that the optimization of bulk material homogeneity should also be actively pursued in any future thermoelectric material research.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.
基金R.K.C.acknowledges grant#NSF(DMR-1508420).Y.W.thanks the support from the Herbert L.Stiles Professorship and ACRI Center IrHtiative from Iowa State University.
文摘Anisotropy and inhomogeneity are ubiquitous in spark plasma sintered thermoelectric devices.However,the origin of inhomogeneity in thermoelectric nanocomposites has rarely been investigated so far.Herein,we systematically study the impact of inhomogeneity in spark plasma sintered bismuth antimony telluride(BiSbTe)thermoelectric nanocomposites fabricated from solution-synthesized nanoplates.The figure of merit can reach 1.18,which,however,can be overestimated to 1.88 without considering the inhomogeneity.Our study reveals that the inhomogeneity in thermoelectric properties is attributed to the non-uniformity of porosity,textures and elemental distribution from electron backscatter diffraction and energy-dispersive spectroscopy characterizations.This finding suggests that the optimization of bulk material homogeneity should also be actively pursued in any future thermoelectric material research.
