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

Using in situ high pressure Raman spectroscopy, two structural changes were observed in a sample of the composition LiLa 5 O 5 (VO 4 ) 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 ) β-LiLa 5 O 5 (VO 4 ) 2 and ( 2 ) β-LiLa 2 O 2 (VO 4 ) or Nd for ( 3 ) LiNd 5 O 5 (VO 4 ) 2 compounds. ( 1 ) crystallizes in the triclinic space group P 1&cmb.macr; 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)°, and γ = 103.54(2)°; a 3D structure was deduced from the ambient pressure polymorph. ( 2 ) also crystallizes in P 1&cmb.macr; 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 [La 2 O 2 ] 2+ layers surrounded by [LiO 4 ] and [VO 4 ] tetrahedra sharing corners and edges. ( 3 ) exhibits a 3D architecture isotypic with AP-LiLa 5 O 5 (VO 4 ) 2. The crucial role of high pressure in such types of synthesis and materials is also discussed. An in situ high pressure Raman spectroscopy study on AP-LiLa 5 O 5 (VO 4 ) 2 allowed evidencing two new phases which were further stabilized using HP-HT synthesis.