Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4) x (PO4)3 − x

Abstract

The LiZr2(AsO4)3 arsenate and LiZr2(AsO4)x(PO4)3 − x solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤ x ≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr2(AsO4)3 (sp. gr. P21/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) A, β = 90.844(2)°, V =1065.03(5) A3, Z = 4; sp. gr. R\(\bar 3\)c, a = 9.1600(4), c = 22.9059(13) A, V = 1664.44(14) A, Z = 6) and LiZr2(AsO4)1.5(PO4)1.5. Their structural frameworks are built up of AsO4 tetrahedra—or (As,P)O4 tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO6 octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr2(AsO4)x(PO4)3 − x with 0 ≤ x ≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.