Crystal and Electronic Structure and Optical Properties of <i>AE</i>₂SiP₄ (<i>AE</i> = Sr, Eu, Ba) and Ba₄Si₃P₈

Abstract

Three new compounds in the AE ‐Si‐P ( AE = Sr, Eu, Ba) systems are reported. Sr 2 SiP 4 and Eu 2 SiP 4 , the first members of their respective ternary systems, are isostructural to previously reported Ba 2 SiP 4 and crystallize in the noncentrosymmetric I 4 2 d (no. 122) space group. Ba 4 Si 3 P 8 crystallizes in the new structure type, in P 2 1 / c (no. 14) space group, mP ‐120 Pearson symbol, Wyckoff sequence e 30 . In the crystal structures of Sr 2 SiP 4 and Eu 2 SiP 4 all SiP 4 tetrahedral building blocks are connected via formation of P–P bonds forming a three‐dimensional framework. In the crystal structure of Ba 4 Si 3 P 8 , Si‐P tetrahedral chains formed by corner‐sharing, edge‐sharing, and P–P bonds are surrounded by Ba cations. This results in a quasi‐one‐dimensional structure. Electronic structure calculations and UV/Vis measurements suggest that the AE 2 SiP 4 ( AE = Sr, Eu, Ba) are direct bandgap semiconductors with bandgaps of ca. 1.4 eV and have potential for thermoelectric applications.