Pressure-induced coordination changes in LiBO2

The coordination and structure changes in LiBO2 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-LiBO2 is found to be compressed easily along the direction of c-axis, resulting in the formation of tetra-coordinated BO4 units. The phase transition boundaries between α- and γ-LiBO2 as well as between amorphous LiBO2 hydrate and γ-LiBO2 have negative pressure–temperature slopes. The conditions for transformation from α- to γ-LiBO2 are lower than that necessary to transform amorphous LiBO2 hydrate to γ-LiBO2. Moreover, the melting curve of LiBO2 has also been determined and has a positive pressure–temperature slope. Upon quenching from high pressure, LiBO2 may not contain [3]B–O–[3]B rings but contain more fraction of [4]B units with increasing pressure.