Abstract
The stability of the phase Cs x[ Ti 2− x 4 □ x 4 ] O 4 , □ = vacancy, in the Cs 2OTiO 2 system has been studied in the temperature range 800−1120°C. The phase has a narrow range of homogeneity with 0.61 < x < 0.65. Structure refinements were carried out for X-ray intensity data from two crystals obtained from melts with TiO 2:CsO 0.5 molar ratios of 2.0 and 3.2. The crystals have orthorhombic symmetry, Immm, a 0 = 3.83, b 0 = 17.00, c 0 = 2.96 Å. The refinements are consistent with the structural model of Hervieu and Raveau ( Rev. Chim. Minér. 18, 642 (1981)) in which (010) corrugated layers of titanium-oxygen octahedra, containing disordered titanium vacancies, are separated by planes of cesium ions. Long-exposure precession photographs showed diffuse superlattice diffraction effects in the form of continuous streaks parallel to b∗ 0 . These have been analyzed in terms of models for two-dimensional ordering of the interlayer cesium ions. Annealing of melted samples below 700°C causes a transformation of the I-centered structure to a C-centered structure of the K x ( M y Ti 2− y )O 4 type in which 3-D ordering of cesium occurs.
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