Syntheses, structures and properties of metal phosphates Pb2Mg(PO4)2, Pb4Zn8(PO4)8 and α-BaZn2(PO4)2

Abstract

Pb₂Mg(PO₄)₂, Pb₄Zn₈(PO₄)₈ and α-BaZn₂(PO₄)₂ have been synthesized by the standard solid-state reaction and their structures were determined by single crystal X-ray diffraction for the first time. Pb₂Mg(PO₄)₂, Pb₄Zn₈(PO₄)₈ and α-BaZn₂(PO₄)₂ crystallize in the monoclinic crystal system, P2₁/c, C2/c and the trigonal crystal system, Pm1, respectively. The structure of Pb₂Mg(PO₄)₂ possesses a three-dimensional framework consisting of MgO₆ octahedra and PO₄ tetrahedra and the Pb²⁺ cations reside in the [Mg₆P₆O₁₂] tunnels. Pb₄Zn₈(PO₄)₈ and α-BaZn₂(PO₄)₂ are two-dimensional layered structures with [Zn₄P₄O₁₆]_∞ layers for Pb₄Zn₈(PO₄)₈ and [Zn₃P₃O₁₂]_∞ honeycomb double layers for α-BaZn₂(PO₄)₂. And in the structure of Pb₄Zn₈(PO₄)₈, there are four different Zn–P–O layers, which is reported for the first time in zinc phosphates. In addition, thermal property analysis, and UV-Vis-NIR diffuse reflectance and infrared spectroscopy were also performed. First-principles theoretical studies were also conducted to aid the understanding of their band structures and densities of states.