A study of the photo-dielectric effect in ferroelectric SBN-75 ceramics of a broad phase transition under light of small intensity is reported. Relations determining kinetics of the infra-low frequency dielectric response under light and after illumination are obtained from experimental measurements revealing the features of the behaviour of relaxation time constants of the dielectric polarisation with temperature.
Raman studies of ostensibly pure congruent, close to stoichiometric and stoichiometric lithium niobate single crystals
and single crystals of lithium niobate containing admixture of Gd3+, Y+, and Mg2+ are reported. The authors have revealed weak Raman bands anomalously narrowing at changes of crystal composition disordering the cation sublattice
and discuss the results with regard to evidence of anomalous ordering of structural units of the cation sublattice
occurring at disordering of the cation sublattice as a whole.
Features of dielectric response to frequencies in the 0.25.1000 Hz range in ceramic samples of BaBi2Nb2O9,
Na0,5Bi8.5Ti2Nb4O27, Na0,5Bi8.5Ti2Ta4O27, and K0,5Bi8.5Ti2Nb4O27 compounds are reported. Considerable relaxation of &egr;'(T) and &egr;"(T) maximums has been observed at all frequencies in BaBi2Nb2O9. Na0,5Bi8.5Ti2Nb4O27 and Na0,5Bi8.5Ti2Ta4O27 are characterised by broad maximums on &egr;'(T) at frequencies below 100 Hz and a weak anomaly in K0,5Bi8.5Ti2Nb4O27 at temperatures well below the paraelectric phase transition. Increasing values of &egr;' are observed at
low temperatures in compounds containing sodium. The observed features of dielectric response are explained by largescale
charge fluctuations in layered ferroelectrics.
Manifestation of relaxor properties in the xPbZn1/3Nb2/3O3-(1-x)PbSc1/2Nb1/203 ceramic solid solution system, similar to those observed in lead magnesium niobates, are reported. Dependence of the effective dielectric permittivity and dielectric loss on the temperature at frequencies of 0.1-10 Hz and different measuring field amplitudes E0 are examined ceramic samples of 0.05PbZn1/3Nb2/3O3-0.95PbSc1/2Nb1/203. It is demonstrated that the temperature at which the dielectric permittivity has a maximum, Tm, decreases with the increase of E0. The dependence of Tm on the frequency in both strong and weak fields is shown to follow the Vogel-Fulcher law, with Voger-Fulcher temperature decreasing with the increase of E0. The results of the dielectric studies in the xPbZn1/3Nb2/3O3-(1-x)PbSc1/2Nb1/203 system are discussed in terms of the transition from the paraelectric to ferroelectric phase through the relaxor and glass states.
Studing of the Raman spectra was established that an optical parameters of oxygen-polyhedral ferroelectric single crystals can be improved by increasing the degree of structural ordering of the cation sublattice along the polar axis by doping them. In this case the impurity ions with the ionic radii close to the radii of the main cations (Li+ and Nb5+) and charges intermediate between those of main cations (1<Z<5) in the area of rather low concentrations were shown to exert an ordering effect on the cation sublattice of a congruent lithium niobate single crystals. Moreover the crystal resistance to laser radiation is also observed to grow. It was determined that the effect of diminishing photorefraction while the crystal is doped correlate well with the discovered ordering of the sublattice along the polar axis and both of them are observed for the same, relatively narrow, range of concentrations and the type of doping impurities.
The surface morphology is studied by use of optical and electron microscopes with respect to production regime (rate and temperature of crystallization) of the 50 - 125 micrometer thick doped YBa2Cu3O7 films obtained by Stokes sedimentation on SrTiO3 ceramic substrate (size 20 mm by 5 mm by 0.5 mm) and firing in air or oxygen following the MTG procedure, performed in the gradient tube furnace. Evolution of thick film structure with regard to temperature and cooling rate is studied.
Due to multifunctionality the transparent ferroelectric ceramics is attractive to solid state chemistry and physics as a promising material for active electro-optic elements. To study doping effects on the technological processing and properties, ceramic samples of Pb1-xZxSc1/2Nb1/2O3, have been prepared, where Z: (1) Ba (0 less than or equal to x less than or equal to 1), (2) rare-earth elements: Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu (x equals 0.1), (3) PbSc1/2Nb1/2O3 doped with 5 wt.% of rare-earth oxides. Ceramic characteristics, dielectric and electro-optical parameters have been measured. Differential thermal analysis (DTA), and x-ray diffraction are used to study the influence of doping on the solid state reactions and to determine the sequence of phases formed during the processes in oxide mixtures in the 500 degree to 950 degree Celsius interval. The pervoskite structure of PbSc1/2Nb1/2O3 (PSN) is found to be formed in a complicated multistage process with several intermediate products during the reaction.
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