Dependence of the Physical Properties on the Cation Ordering in the New Ternary Phosphide ZnCu2P8

Abstract

: The air-stable phosphide, ZnCu2P8, was synthesized from its elements in gram amounts. It crystallizes in the Cu2.5In0.5P8 structure type [C2/c, Z = 4, a = 1110.8(2) pm, b = 964.7(2) pm, c = 752.7(1) pm, β = 110.027(3)°], and is the first ternary phosphide in the system Zn/Cu/P. Its crystal structure consists of two-dimensional, layered polyphosphide-anions, separated by tetrahedrally-coordinated cations. 135 symmetry independent configurations, each with a different and specific Zn2+ and Cu+ arrangement, where explored with density functional methods. Whereby, each of the 135 cation ordering pattern has a diverse bandgap, and the total energies vary in the range of 1 eV. As several configurations with low energy are close in energy, an intrinsic disorder is discussed as origin of the promising low lattice thermal conductivity, observed.