Synthesis, crystal structure, and thermoelectric properties of ternary phosphide $BaCu_5P_3$

Abstract

A new copper-phosphide, $BaCu_5P_3$ was synthesized by a high-temperature solid-state route and salt flux method. The crystal structure of $BaCu_5P_3$ was determined using single crystal X-ray diffraction. $BaCu_5P_3$ crystallizes in the orthorhombic space group Pnnm (No. 58) with unit cell parameters of a ​= ​12.018 (1) $\AA$, b ​= ​23.762 (2) $\AA$, and c ​= ​3.984 (1)$\AA$ with Z ​= ​8. $BaCu_5P_3$ crystallizes in a new structure type. A complicated three-dimensional framework built by Cu–Cu and Cu–P interactions hosts Ba cations in $BaCu_5P_3$ According to differential scanning calorimetry, $BaCu_5P_3$ decomposes to $BaCu_2P_4$ and $BaCu_8P_4$ around 1180 (5)K. Theory calculation and thermoelectric measurements confirm the metallic nature of $BaCu_5P_3$ The experimentally measured moderate thermal conductivity of $BaCu_5P_3$ is mainly originated from its complex crystal structure. The Seebeck coefficient of $BaCu_5P_3$ is positive and low, ranging from 10 ​K to 400 ​K.