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

International audienceUsing in situ high pressure Raman spectroscopy, two structural changes were observed in a sample of composition LiLa5O5(VO4)2. Taking this account and by combining different conditions, three new compounds have been further obtained from high pressure – high temperature synthesis. Their crystal structure description is done using the antiphase approach, that implies the presence of oxygen-centered [OLn4] building units, where Ln is La for (1) β-LiLa5O5(VO4)2 and (2) β-LiLa2O2(VO4) or Nd for (3) LiNd5O5(VO4)2 compounds. (1) crystallizes in the triclinic space group P-1 with unit cell parameters of a = 5.8167(15) Å, b =12.2954(28) Å, c =18.7221(69) Å, α =102.03(2)°, β = 98.76(2)°, γ = 103.54(2)° and a 3D structure deduced from the ambient pressure polymorph. (2) crystallizes as well in P-1 with a = 5.8144(7) Å, b = 5.8167(7) Å, c = 8.5272(1)Å, α = 98.184(7)°, β = 100.662(7)° and γ = 92.579(7)°. 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 type of synthesis and materials is also discussed