The infrared absorption spectra of polycrystalline LaMnO 3 and CaMnO 3 measured in the frequency range of the transverse optical phonons are reported, discussed, and compared with calculations of the lattice dynamics. For LaMnO 3 the measured spectrum is consistent with the expected orthorhombic structure. For CaMnO 3 the spectrum reflects a symmetry lower than that of a cubic perovskite. We find a close correspondence between the spectra of the two materials which suggests a similarity in their structures. ͓S0163-1829͑99͒09441-2͔

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PbZrr,,7~Tio.~O3 thin film deposited by a sol-gel technique on sapphire substrates were measured between room temperahue and 650'C. The speeua were fined with a classical oscillator model to calculate the dielectric respame. Polar-mode parameten are more accurate than data on bulk Ceramic materials and are i n good agreemen1 with them. An analysis of the sofl-mode behaviour and comparison with the low-fwuency permittivity data clwly indicate Ihe existence of additional relaxation that is always present in thc several cm-' range. even at room temperature,

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Infrared reflectivity and Raman spectra of hot-pressed PLZT 8/65/35,9.5/65/35 and 2/95/5 ceramics show only weak temperature changes in the first two (ferroelectric) compositions but much richer spectra and pronounced temperature changes in the third (antiferroelectric) composition, including a soft phonon mode.

We report on the first quantitative evaluation of the soft-mode behaviour of the relaxor PLZT 9.5/65/35. The transmission spectra of a PLZT thin film deposited on a sapphire substrate were measured in the 4-350 cm −1 region at temperatures from 300 up to 523 K, and in the 15-350 cm −1 range at 8-300 K. We fitted the spectra using the model of classical oscillators, and calculated the parameters of the observed lattice modes. The results were compared with those for bulk ceramics, and satisfactory agreement was achieved. The soft mode is heavily damped, and below room temperature it shows a strong hardening on cooling. Above room temperature, its eigenfrequency levels off, but the corresponding dielectric loss maximum continues to soften weakly down to ∼33 cm −1 at 523 K, where the mode becomes overdamped. The lower-frequency data require an additional relaxation below the measured range. Comparison of all of the available data at room temperature points to strong polydispersive losses in the 10 10 -10 12 Hz range, and another dispersion region at lower frequencies. We assign them to fluctuations of the polar nanocluster volume, and to reorientations of the cluster polarization, respectively. Their contribution to the low-frequency permittivity is much stronger than that of the soft mode.

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