Structure determination, electronic and optical properties of NaGe 2P 3O 12 and Cs 2GeP 4O 13

Abstract

Two alkali–metal germanium phosphates, namely, NaGe 2P 3O 12 and Cs 2GeP 4O 13, have been synthesized by the solid-state reactions and their structures determined by single-crystal X-ray diffraction. The structure of NaGe 2P 3O 12 features a Nasicon-type structure, crystallizing in space group R 3 ¯ with a = 8.109(2), c = 21.536(8) (Å), V = 1226.3(6) Å 3, Z = 6, R 1 = 0.0383 and ωR = 0.0960; Cs 2GeP 4O 13 crystallizes in triclinic space group P 1 ¯ with a = 9.420(3), b = 10.209(4), c = 12.407(4) (Å), α = 104.136(6), β = 108.132(5), γ = 95.338(6)°, V = 1081.0(7) Å 3, Z = 2, R 1 = 0.0445 and ωR = 0.1117. Additionally, the calculations of band structure and density of states were performed with the density functional theory method for the title compounds. The results show that the solid-state compounds of NaGe 2P 3O 12 and Cs 2GeP 4O 13 are insulator with indirect band-gap of 3.529 and 3.888 eV, respectively.