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Appearance of the polar nanoregions (PNR) and their manifestation in the dielectric spectra is discussed for lead-free Ba(ZrxTi1−x)O3(BZT-x) and (Na1/2Bi1/2)TiO3(NBT) ceramics. Phonon softening is not as pronounced as in the lead-based relaxors, but the relaxation contribution is dominating in all cases, caused by the dynamics of the off-centred ions (Ti4+, Bi3+, Pb2+). In the lead-based relaxors, where there is no relation between the quenched chemical clusters at the B-sites and PNR, which concern the A-site Pb-ion correlations, the relaxation dynamics follows the Vogel–Fulcher behaviour with a clear freezing. However, in BZT and NBT, the PNR are smaller, since they are localised within the small quenched chemical clusters of BaTiO3and BiTiO3, respectively. Their dynamics is Arrhenius-like, which indicates hopping of the off-centred Ti4+and Bi3+ions, respectively, without their complete freezing. BZT can be classified as a dipolar glass and NBT as a nanoscopic ferroelectric with peculiar Bi-ion dynamics. [ABSTRACT FROM PUBLISHER]

Dynamics of the main dielectric anomaly in Na1/2Bi1/2TiO3(NBT) were studied by time-domain THz and microwave spectroscopy, using also previously published data and their new overall fits. Above the dielectric maximum temperatureTm≈ 600 K, the response consists of coupled sub-THz oscillator and a relaxation mode, assigned to strongly anharmonic Bi-ion vibrations and hopping, whose slowing down explains the paraelectric-like permittivity increase toTm. BelowTm, the main relaxation continues slowing down and additional relaxation, assigned to quasi-Debye losses, appears in the 1011 Hz range. The oscillator hardens on cooling and takes over the whole oscillator strength. The permittivity decrease belowTmis caused by the reduced strength of the relaxations due to dominance of the rhombohedral phase within the coexistence region with the tetragonal phase. The anharmonic dynamics of Bi are supported by previous structural studies. NBT represents a hybrid between standard and relaxor ferroelectric behaviour. [ABSTRACT FROM AUTHOR]

We report on the experimental and theoretical study of the lattice dynamics in Ba0.7Sr0.3TiO3 in 20-900 K temperature range. Complex dielectric response in the terahertz and far infrared range was evaluated from the time-domain THz transmission spectra and infrared reflectivity by means of damped harmonic oscillator models in classical and factorized form of the dielectric function. The anisotropic dielectric function in the ferroelectric phases was extracted using the Bruggeman model of the effective medium approximation. The fitted parameters of the temperature-dependent Slater-type vibrations (soft mode and central mode, CM) were compared with those obtained from ab initio simulations. The role of the lattice phonons and CM in the dielectric anomaly is discussed. [ABSTRACT FROM AUTHOR]

The article discusses various reports published within the issue. Articles published within the issue were taken from the XVII Czech -- Polish Seminar held in Znojmo, Czech Republic on May 22-26, 2006. The topics covered include the physics of the ferroelectrics and relaxor ferroelectrics with perovskite structure as well as phase transitions, aspects of ferroelectricity and structural phase transitions.