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A polycrystalline sample of BaTi0.85(Fe1/2Nb1/2)0.15O3 is synthesized by high temperature solid state reaction technique. This sample crystallizes in cubic pervoskite structure at room temperature. The dielectric properties have been investigated at temperature range from 80 to 450 K at various frequencies (100–107 Hz). Frequency dielectric dispersion phenomena in a BaTi0.85(Fe1/2Nb1/2)0.15O3 ceramic has been analyzed by impedance spectroscopy in the temperature range from 250 to 450 K. The Cole-Cole relaxation equation modified by introducing the conductivity was used to describe the experimental dielectric spectra of a high permittivity. Excellent agreement has been obtained in wide frequency domain (100–107 Hz) between the measured and calculated permittivities in the 250–450 K temperature range. The dielectric relaxation frequency obeys the Arrhenius behavior with activation energy of 0.181 eV. A separation of the grain and grain boundary properties has been achieved using an equivalent circuit model. The different parameters of this circuit have been determined using impedance and modulus spectroscopy studies. The inner grain conductivity also obeys the Arrhenius low behavior with activation energy of 0.183 eV. The dielectric relaxation and the inner grain conductivity have thus similar activation energies which suggest a link between these two phenomena. [ABSTRACT FROM AUTHOR]

Unpoled and efficient nonlinear optical (NLO) poled sodium niobium borophosphate glasses have been studied by means of dielectric spectroscopy. The thermal poling process induces a dielectric relaxation that gradually vanishes on heating for T>=500 K. The data are interpreted by a two-layer (Maxwell-Wagner) model, consisting of a bulk and a Na+ poor surface layer with lower conductivity. Our results suggest that the ion transport is due to hopping mechanism implying at least Na+. All the dielectric results are in full agreement with previous optical analyses. This is an example of poled glasses where an efficient NLO response is directly correlated to the conductivity of the material enhanced by a high alkali loading. [ABSTRACT FROM AUTHOR]

The transitions from a relaxor state to a rhombohedral ferroelectric phase are studied in different Pb(Sc[sub 1/2]Nb[sub 1/2])O[sub 3] ceramics characterized by varied chemical ordering on the B site of the perovskite structure. The transition may arise at different temperatures, eventually in two stages in the same sample. The dielectric response reflects the density of polar domains and changes from relaxorlike (numerous polar nanodomains in the nearly fully ordered sample) to the relaxor-normal ferroelectric transition (in the disordered sample). The chemical order degree, as well as the spatial inhomogeneity of this order have to be taken into account to understand this behavior. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses the performance of electrical measurements in different Pb[(Mg1/3Nb2/3)0.9Ti0.1]O3 ceramics exhibiting a spontaneous relaxor to ferroelectric transition. Dependence of relaxor behavior and phase transition on lead vacancies content; Increase of ordered domains and reduction of interactions between polar clusters.