Structural characterizations of lithium gallium phosphates, analogous to the amblygonite-montebrasite series

LiGaPO4(OH) and LiGaPO4F1-delta (OH)(delta) (delta approximate to 0.26) were hydrothermally synthesized at 180degreesC for 36 hours. Both compounds were analogous to the lithium aluminophosphates belonging to the minerals series of montebrasite (pure OH form) and amblygonite (mixed OH,F form). The solids crystallize in the triclinic cell (PI) with a = 7.1487(2), b = 5.3005(2), c = 5.0877(2) A, alpha = 97.988(2)degrees, beta = 109.035(2)degrees, gamma = 106.630(2)degrees, V = 168.776(9) Angstrom(3) (for LiGaPO4(OH)) and a = 7.1748(2), b = 5.2639(1), c = 5.1022(1) A, alpha = 98.015(2)degrees, beta = 108.854(2)degrees, gamma = 107 035(2)degrees, V = 168.421(8) Angstrom(3) (for LiGaPO4F1-delta (OH)(delta), delta approximate to 0.26). The structure of the fluorinated form LiGaPO4(OH,F) was refined from conventional X-ray powder diffraction data by using the Rietveld method. The three-dimensional framework is composed of infinite chains of corner-shared gallium octahedra GaO4(OH,F)2 linked to each other through the phosphate groups PO4. The lithium ions reside within the 6-ring channels (along [010] and [001]). (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.