Electronic Structure Analysis of the A10 Tt2 P6 System (A=Li-Cs; Tt=Si, Ge, Sn) and Synthesis of the Direct Band Gap Semiconductor K10 Sn2 P6.

Abstract

Investigating the relationship between atomic and electronic structures is a powerful tool to screen the wide variety of Zintl phases for interesting (opto-)electronic properties. To get an insight in such relations, the A10 Tt2 P6 system (A=Li-Cs; Tt=Si-Sn) was picked as model system to analyse the influence of structural motives, combination of elements and their properties on type and width of the band gaps. Those compounds comprise two interesting structural motives of their anions, which are either monomeric trigonal planar TtP3 5- units which are isostructural to CO3 2- or [Tt2 P6 ]10- dimers which correspond to two edge-sharing TtP4 tetrahedra. The A10 Tt2 P6 compounds were structurally optimized for both polymorphs and subsequent frequency analysis, band structure as well as density of states calculations were performed. The Gibbs free energies were compared to determine temperature dependent stability, where Na10 Si2 P6 , Na10 Ge2 P6 and K10 Sn2 P6 were found to be candidates for a high temperature phase transition between the two polymorphs. Additionally, the unknown, but predicted compound K10 Sn2 P6 was synthesized and characterized by single crystal and powder x-ray diffraction. It crystalizes in the monoclinic space group P 21 /n and incorporates [Sn2 P6 ]10- edge sharing double tetrahedra. It was determined to be a direct band gap semiconductor with a band gap of 2.57 eV.