Crystal and Electronic Structure and Optical Properties of AE2SiP4 (AE = Sr,Eu, Ba) and Ba4Si3P8

Three new compounds in the AE‐Si‐P (AE = Sr, Eu, Ba) systems are reported. Sr₂SiP₄ and Eu₂SiP₄, the first members of their respective ternary systems, are isostructural to previously reported Ba₂SiP₄ and crystallize in the noncentrosymmetric I4 2d (no. 122) space group. Ba₄Si₃P₈ crystallizes in the new structure type, in P2₁/c (no. 14) space group, mP‐120 Pearson symbol, Wyckoff sequence e³⁰. In the crystal structures of Sr₂SiP₄ and Eu₂SiP₄ all SiP₄ tetrahedral building blocks are connected via formation of P–P bonds forming a three‐dimensional framework. In the crystal structure of Ba₄Si₃P₈, 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 AE₂SiP₄ (AE = Sr, Eu, Ba) are direct bandgap semiconductors with bandgaps of ca. 1.4 eV and have potential for thermoelectric applications.