High pressure exploration in the Li–Ln–V–O system. Issue 39 (28th September 2020) - Zadoya, A. I.
Abstract : An in situ high pressure Raman spectroscopy study on AP-LiLa5 O5 (VO4 )2 allowed evidencing two new phases which were further stabilized using HP–HT synthesis. Abstract : Using in situ high pressure Raman spectroscopy, two structural changes were observed in a sample of the composition LiLa5 O5 (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 [OLn4 ] building units, where Ln is La for (1 ) β-LiLa5 O5 (VO4 )2 and (2 ) β-LiLa2 O2 (VO4 ) or Nd for (3 ) LiNd5 O5 (VO4 )2 compounds. (1 ) crystallizes in the triclinic space group P 1̄ 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 1̄ 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 [La2 O2 ] 2+ layers surrounded by [LiO4 ] and [VO4 ] tetrahedra sharing corners and edges. (3 ) exhibits a 3D architecture isotypic with AP-LiLa5 O5 (VO4 )2. The crucial role of high pressure in such types of synthesis and materials is also discussed.