Synthesis and crystal structure of novel complex phosphate Li 5 Cu 2 Al(PO 4 ) 4

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Synthesis and Crystal Structure of Novel Complex Phosphate Li5Cu2Al(PO4)4 L. V. Shvanskaya and O. V. Yakubovich Moscow State University, Moscow, 119234 Russia email: [email protected] Received April 29, 2013

Abstract—A new complex phosphate Li5Cu2Al(PO4)4 has been obtained by the flux method in the Cs–Li– Cu–V–P–O system. Its crystal structure has been determined by Xray diffraction (R1 = 2.74%) to be as fol lows: sp. gr. P1, a = 4.860(5) Å, b = 7.788(5) Å, c = 8.324(5) Å, α = 69.542(5)°, β = 90.016(5)°, γ = 75.318(5)°, Z = 1, and V = 284.2(4) Å3. The compound under study has a dense structure and a three dimensional framework build up of [LiO5], [AlO6], [Cu/LiO5], and [CuO4] polyhedra and [PO4] tetrahedra. A comparative crystalchemical analysis of two isotypic compounds with a general formula Li5Cu2M(PO4)4 (M = Fe, Al) has been performed. Topological relations between the Na2Mg5(PO4)4 and Li5Cu2M(PO4)4 crystal structures, which are characterized by different cationic compositions, are revealed. DOI: 10.1134/S1063774514020230

INTRODUCTION Within the search for new materials with important functional properties, attempts have been made to synthesize complex phosphates of alkali and transition metals. The establishment of high ionic conductivity for materials based on LiМPO4 (M = Fe, Mn, Co, Ni) [1–3] and Li3M2(PO4)3 [3–5] (M = Fe, Ti, V, Al/Ge), characterized by olivine or NASICONlike crystal structures (dense 3D metal phosphate frameworks with “channels,” along which Li+ ions can be trans ported), is a source of constant interest in Licontain ing phases of this type. Complex Cucontaining phos phates also attract much attention in view of their antiferromagnetic properties. Copper atoms in crystal structures of oxysalts, in correspondence with the Jahn–Teller effect, may have different coordination geometries: square, tetrahedral, pyramidal, or octahe dral. Monomers, dimers, or trimers of Cu polyhedra in phosphate structures are combined via phosphorus tetrahedra into structures of different dimensions: chain, lamellar, or framework ones. This fact deter mines the large crystalchemical variety of copper containing phosphates. The combination of fragments that are responsible for both ionconducting and mag netic properties in one crystal structure is favorable for finding new multifunctional compounds and design ing new technologically important materials on their basis. Currently, a rather limited number of crystal struc tures of phosphates containing simultaneously lithium and copper atoms have been investigated. These are Li2CuP2O7 [6, 7], LiCu(PO3)3 [8], Li2Cu2P6O18 [9], Li2Cu5(PO4)4 [10, 11], and Li5Cu2Fe(PO4)4 [12].

Note that lithium and copper atoms in the former three compounds fully occupy their own crystallo graphic positions, whereas the crystal structures of the two latter compounds are characterized by the pres ence of mixed Li/Cu sites. In this paper we report the results of our synthesis and Xray diffraction study of a new defect orthophos phate