LiB3O5 crystal structure at 20, 227 and 377 °C

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, MoKα-radiation, anharmonic approximation, orthorhombic; Pna21; Z=4; 20 °C (a=8.444, b=7.378, c=5.146 Å, 1411 F(hkl), R=0.022); 227 °C (a=8.616, b=7.433, c=5.063 Å, 1336 F(hkl), R=0.026), 377 °C (a=8.746, b=7.480, c=5.013 Å, 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 Å 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 α-Na2B8O13 and α-CsB5O8. At the same time these groups rotate relative to each other like hinges leading to extremely anisotropic thermal expansion (αa=101, αb=31, αc=−71, αv=60×10−6 °C−1, 20–530 °C, HTXRPD data).