The chalcogenides Tl_(2)NdAg_(3)Q_(4)(Q=Se,Te)were prepared by heating the elements in stoichiometric ratios under exclusion of air between 973 K and 1073 K.Both compounds adopt new structure types,with Tl_(2)NdAg_(3)...The chalcogenides Tl_(2)NdAg_(3)Q_(4)(Q=Se,Te)were prepared by heating the elements in stoichiometric ratios under exclusion of air between 973 K and 1073 K.Both compounds adopt new structure types,with Tl_(2)NdAg_(3)Se_(4) crystallizing in the space group Pnma with a=15.9937(14)Å,b=4.3420(4)Å,c=14.3676(12)Å,V=997.75(15)Å^(3),Z=4,while Tl_(2)NdAg_(3−x)Te_(4) adopts a different structure with related motifs,crystallizing in the noncentrosymmetric space group Cmc2_(1) with a=4.5968(2)Å,b=16.8620(6)Å,c=44.7131(15)Å,V=3465.8(2)Å^(3),Z=12,when x=0.05.In both cases,linear chains of[AgQ4]tetrahedra are interconnected via common corners and edges to build a three-dimensional network,which encompasses the Tl and Nd atoms in linear channels.The differences lie in their three-dimensional connection,resulting in a larger,noncentrosymmetric unit cell of the telluride.Electronic structure calculations indicate semiconducting properties,in accord with the transport property measurements in both cases.A special feature of both materials is the extraordinarily low thermal conductivity.展开更多
基金financial support in form of a Discovery Grant from the Natural Sciences and Engineering Research Council of Canada.
文摘The chalcogenides Tl_(2)NdAg_(3)Q_(4)(Q=Se,Te)were prepared by heating the elements in stoichiometric ratios under exclusion of air between 973 K and 1073 K.Both compounds adopt new structure types,with Tl_(2)NdAg_(3)Se_(4) crystallizing in the space group Pnma with a=15.9937(14)Å,b=4.3420(4)Å,c=14.3676(12)Å,V=997.75(15)Å^(3),Z=4,while Tl_(2)NdAg_(3−x)Te_(4) adopts a different structure with related motifs,crystallizing in the noncentrosymmetric space group Cmc2_(1) with a=4.5968(2)Å,b=16.8620(6)Å,c=44.7131(15)Å,V=3465.8(2)Å^(3),Z=12,when x=0.05.In both cases,linear chains of[AgQ4]tetrahedra are interconnected via common corners and edges to build a three-dimensional network,which encompasses the Tl and Nd atoms in linear channels.The differences lie in their three-dimensional connection,resulting in a larger,noncentrosymmetric unit cell of the telluride.Electronic structure calculations indicate semiconducting properties,in accord with the transport property measurements in both cases.A special feature of both materials is the extraordinarily low thermal conductivity.
