Synthesis, crystal and electronic structures, and physical properties of a new quaternary phosphide Ba4Mg2+δCu12−δP10 (0 < δ < 2)

Abstract

A new quaternary phosphide, Ba₄Mg_2+δCu_12−δP₁₀ (0 < δ < 2), was synthesized via solid state reactions of the elements and its crystal structure was determined by single crystal X-ray diffraction. Ba₄Mg_2.8Cu_11.2P₁₀ crystallizes in the monoclinic system space group P2₁/m (no. 11) with unit cell parameters of a = 8.258(1) Å, b = 4.009(1) Å, c = 15.260(2) Å, β = 97.851(2)°, and Z = 1. The crystal structure of Ba₄Mg_2+δCu_12−δP₁₀ is composed of large two-dimensional Ba₂Mg_2+δCu_12−δP₁₀ blocks stuck along the [001] direction. Each block is terminated by unique Cu₄P₃ layers with a PbO-like Mg_δCu_2−δP₂ layer inside the block. Cu₄P₃ and Mg_δCu_2−δP₂ layers are linked together in the block by Cu–P bonds. All Mg and half of the Ba cations are situated in the large channels inside the blocks while the other half of Ba atoms are arranged in corrugated layers separating the blocks. The metallic properties of Ba₄Mg_2.8Cu_11.2P₁₀ were predicted based on electronic structure calculations and confirmed by resistivity measurements. Ba₄Mg_2.8Cu_11.2P₁₀ exhibits moderate thermal conductivity, 13.4 W m⁻¹ K⁻¹ at 400 K, which mainly originates from the lattice contribution of 9.1 W m⁻¹ K⁻¹ at 400 K.