Synthesis, crystal structure, and ionic conductivity of a new layered metal phosphate, Li2Sr2Al(PO4)(3)

摘要

A new layered metal phosphate, Li2Sr2Al(PO4)(3), was synthesized in the form of either a single-crystal or polycrystalline powder using the molten hydroxide flux method or a solid-state reaction, respectively. Li2Sr2Al(PO4)(3) crystallizes to the P2(1) (Z=4) monoclinic space group with lattice parameters a approximate to 4.95 angstrom, b approximate to 22.06 angstrom, c approximate to 8.63 angstrom, and beta approximate to 91.5 degrees. The structure is composed of stacked [LiSrAl(PO4)(2)] layers alternating regularly with [LiSrPO4] layers. In the [LiSrAl(PO4)(2)] sublattice, the AlO6 octahedra and PO4 tetrahedra are tilted cooperatively to form an anionic, corrugated, two-dimensional [Al(PO4)(2)](3-) framework that can be regarded as a "distorted-glaserite" structure. The [LiSrPO4] sublattice is that of a layered block containing a six-membered ring formed from alternating linkages of LiO4 and PO4 tetrahedra. The six-membered rings show a boat-type arrangement with the up(U) or down(D) pointing sequence, UUDUUD. The interspace between the two sublattices generates a two-dimensional pathway for Li+ ion conduction. The impedance measurement indicated that Li2Sr2Al(PO4)(3) had a moderate ion conductivity (sigma approximate to 1.30 x 10(-4) S cm(-1) at 667 K), with an activation energy E-a approximate to 1.02 eV. (C) 2016 Elsevier Inc. All rights reserved.