Noncentrosymmetric cubic thio- and selenogermanates: A_(0.5)M_(1.75)GeQ_4 (A=Ag, Cu, Na; M=Pb, Eu; Q=S, Se)

摘要

Five new isostructural cubic thiogermanates with the formula A_(0.5)M_(1.75)GeQ_4 (A=Ag, Cu, Na; M=Pb, Eu; Q=S, Se) have been prepared by direct combination of stoichiometric amounts of the elements. The compounds crystallize in the noncentrosymmetric space group I-43d with Z=16 and a=14.0291(5) A for Ag_(0.5)Pb_(1.75)GeS_4, a=14.5949(19) A for Ag_(0.5)Pb_(1.75)GeSe_4, a=13.9491(14) A for Ag_(0.5)Eu_(1.75)GeS_4, A = 13.8145(9) A for Cu_(0.5)Pb_(1.75)GeS_4 and A = 14.662(4) A for Na_(0.5)Pb_(1.75)GeSe_4. The adopted structure is similar to that of Ba_3CdSn_2S_8, and features tetrahedral [GeQ_4]~(4-) building blocks. These compounds are semiconductors with energy gaps (Eg) ranging from 1.48 to 1.83 eV.