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Abstract: The coordination and structure changes in LiBO2 have been studied at high pressure and temperature up to 5GPa 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. [Copyright &y& Elsevier]

Abstract: This work presents a comprehensive study on phase transitions in LiAlO2 system at high pressures and temperatures (0.5–5.0GPa and 300–1873K, respectively), as well as the phase stability for polymeric phases of LiAlO2 in the studied P–T space by X-ray diffraction (XRD). Besides the previously described polymorphic hexagonal α-phase, orthorhombic β-phase and tetragonal δ-phase, a possible new phase of LiAlO2 was observed after the tetragonal γ-LiAlO2 sample was treated at 5.0GPa and 389K. The stable regimes of these high-pressure phases were defined through the observation of coexistence points of the polymeric phases. Our results revealed that LiAlO2 could experience structural phase transitions from γ-LiAlO2 to its polymorphs at lower pressures and temperatures compared to the reported results. Hexagonal α-LiAlO2 with highly (003) preferential orientation was prepared at 5.0GPa and 1873K. [Copyright &y& Elsevier]