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The frequencies of the softest polar optic phonons of tetragonal SrTiO3 are accurately determined using high-resolution hyper-Raman spectroscopy on oriented-domain crystals. The splitting of the polar soft mode in the tetragonal phase is quantitatively related to the 105 K structural transition, i.e., to the rotation of the oxygen octahedra and to the associated macroscopic strains. In addition to quantum fluctuations, these tetragonal distortions are found to be essential in preventing the ferroelectric transition.

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A new lithium iron oxide, LiFeO 2 , with a tunnel structure was synthesized by an ion exchange reaction between the host material, ␤-FeOOH, with LiOH•H 2 O, and its cathodic properties for lithium cells were examined. The ion exchange reaction was carried out by solvothermal reactions using various alcohols and the new phase was obtained for the reaction at 110°C. Its structure, determined by X-ray diffraction measurements using Rietveld analysis, has the hollandite-type tunnel structure. Lithium cells consisting of the new LiFeO 2 cathodes and lithium anodes showed good charge and discharge reversibility in the voltage range, 1.5 to 4.5 V. The lithium intercalation and deintercalation mechanism was characterized using X-ray diffraction results, Mo ¨ssbauer spectroscopy, and electrochemical measurements.