Pressure-induced coordination changes in LiBO 2

Abstract

The coordination and structure changes in LiBO 2 have been studied at high pressure and temperature up to 5 GPa and 1500 °C using in-situ high-pressure differential thermal analysis, infrared absorption spectra and X-ray diffraction. The layer framework structure of α-LiBO 2 is found to be compressed easily along the direction of c-axis, resulting in the formation of tetra-coordinated BO 4 units. The phase transition boundaries between α- and γ-LiBO 2 as well as between amorphous LiBO 2 hydrate and γ-LiBO 2 have negative pressure–temperature slopes. The conditions for transformation from α- to γ-LiBO 2 are lower than that necessary to transform amorphous LiBO 2 hydrate to γ-LiBO 2. Moreover, the melting curve of LiBO 2 has also been determined and has a positive pressure–temperature slope. Upon quenching from high pressure, LiBO 2 may not contain [3]B–O– [3]B rings but contain more fraction of [4]B units with increasing pressure.