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The temperature dependence of the ir reflection spectrum (A(1)-type modes) of LiTaO(3) is reported from room temperature up to ~1300 K, that is, 400 K above the ferroelectric-paraelectric phase transition. Results for the isomorphic compound LiNbO(3) are also presented. Certain phonon resonance lines are found asymmetric. Several dielectric function models are discussed. Certain advantages of ir reflectivity spectroscopy are emphasized.

We report the investigation of the (Ba,Sr)TiO3 (BST) system of technological importance for microwave applications. The development of the combinatorial method enabled us to grow and study a library of samples ranging from BaTiO3 to SrTiO3 (ST) deposited on MgO substrate. The spatial control of the stoichiometry and of the structure has been evidenced and probed using energy dispersive x-ray spectroscopy, high resolution x-ray diffraction, and Raman spectroscopy. A global and coherent picture emerged from the complex interplay between the epitaxial/thermal stress and stoichiometry changes. Taking into account elastic interactions with the substrate we present subtle symmetry changes in the BST library in comparison with the bulk phase diagram such as tetragonal distortion observed on the ST side. Finally underdamped soft mode hardening and polar modes are detected on the high barium and strontium compositions, respectively, highlighting fundamental dynamical/structural differences with their bulk counterparts.

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