Pressure-induced structural transformations in lanthanide titanates: La2TiO5 and Nd2TiO5

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The structure of orthorhombic rare earth titanates of La 2TiO5 and Nd2TiO5, where Ti cations are in five-fold coordination with oxygen, has been studied at high pressures by X-ray diffraction (XRD), Raman scattering measurements, and quantum mechanical calculations. Both XRD and Raman results indicated two pressure-induced phase transitions during the process. An orthorhombic super cell (a×b×2c) formed at a pressure between 6 and 10 GPa, and then transformed to a hexagonal high-pressure phase accompanied by partial decomposition. The hexagonal high-pressure phase is quenchable. Detailed structural analysis indicated that the five-coordinated TiO5 polyhedra remain during the formation of super cell, but the orthorhombic-to-hexagonal phase transition at high pressures is a reconstructive process, and the five-fold TiO coordination increased to more than 6. This phase transition sequence was verified by quantum mechanical calculations. © 2010 Elsevier Inc. All rights reserved.

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Journal of Solid State Chemistry

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