High pressure exploration in the Li–Ln–V–O system

Abstract

Using in situ high pressure Raman spectroscopy, two structural changes were observed in a sample of the composition LiLa5O5(VO4)(2). Taking this into account and by combining different conditions, three new compounds were further obtained from high pressure-high temperature synthesis. Their crystal structure description was done using the antiphase approach, which implies the presence of oxygen-centered [OLn(4)] building units, where Ln is La for (1) beta-LiLa5O5(VO4)(2) and (2) beta-LiLa2O2(VO4) or Nd for (3) LiNd5O5(VO4)(2) compounds. (1) crystallizes in the triclinic space group P (1) over bar with unit cell parameters of a = 5.8167(15) angstrom, b = 12.2954(28) angstrom, c = 18.7221(69) angstrom, alpha = 102.03(2)degrees, beta = 98.76(2)degrees, and gamma = 103.54(2)degrees; a 3D structure was deduced from the ambient pressure polymorph. (2) also crystallizes in P (1) over bar with a = 5.8144(7) angstrom, b = 5.8167(7) angstrom, c = 8.5272(1) angstrom, alpha = 98.184(7)degrees, beta = 100.662(7)degrees and gamma = 92.579(7)degrees. It shows a 2D structure with [La2O2](2+) layers surrounded by [LiO4] and [VO4) tetrahedra sharing corners and edges. (3) exhibits a 3D architecture isotypic with AP-LiLa5O5(VO4)(2). The crucial role of high pressure in such types of synthesis and materials is also discussed.