LiB3O5 crystal structure at 20, 227 and 377 degrees C

摘要

Crystal structure of LiB3O5 (a framework of [B3O5](-) rings and Li atoms located in interspaces) was refined at high temperatures using single-crystal X-ray diffraction, MoK alpha-radiation, anharmonic approximation, orthorhombic; Pna2(1); Z = 4; 20 degrees C (a = 8.444, b = 7.378, c = 5.146 angstrom, 1411 F(hkl), R = 0.022); 227 degrees C (a = 8.616, b = 7.433, c = 5.063 angstrom, 1336 F(hkl), R = 0.026), 377 degrees C (a = 8.746, b = 7.480, c = 5.013 angstrom, 1193 F(hkl), R = 0.035). A high mobility of Li atoms and their highly asymmetric vibrations are revealed. Ellipsoid of Li thermal vibrations is oviform. Li is shifted on heating to 0.26 angstrom mainly along a-axis causing high thermal expansion in this direction; Li temperature factors are multiplied by 4 on heating. Rigid boron-oxygen groups in LiB3O5 remain practically stable on heating similar to alpha-Na2B8O13 and alpha-CsB5O8. At the same time these groups rotate relative to each other like hinges leading to extremely anisotropic thermal expansion (alpha(a) = 101, alpha(b) = 31, alpha(c) = -71, alpha(v) = 60 x 10(-6) degrees C-1, 20-530 degrees C, HTXRPD data). (c) 2005 Published by Elsevier Inc.