Synthesis, Structure, and Electronic Structure of the Ternary Sulfide La₇Sb₉S₂₄

Abstract

A ternary sulfide exists on the quasi-binary section La2S3−Sb2S3, La7+δSb9-δS24. This material exhibits a small but significant phase range with at least −0.296(4) ≤ δ ≤ 0.134(6). La7+δSb9-δS24 forms a new structure type, space group P21/c, with a = 8.7115(9) Å, b = 14.3450(15) Å, c = 15.2657(16) Å, β = 90.105(2)° (Z = 2) for δ = 0.13. This structure contains chains of severely distorted SbS5 square antiprisms, interconnected by eight- and nine-coordination La atoms. One position is mixed-occupied by La and Sb, with the La content ranging at least from 57% to 35%. La7Sb9S24 is a blackish material with a computed gap >1.5 eV.