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A polycrystalline sample of Ba[Ti.sub.0.85]([[Fe.sub.1/2][Nb.sub.1/2]].sub.0.15])[O.sub.3] is synthesized by high temperature solid state reaction technique. The x-ray diffraction of the sample at room temperature shows a cubic phase and a high value of dielectric permittivity in a wide temperature interval approximately (200-450K) is obtained in Ba[Ti.sub.0.85]([[Fe.sub.1/2][Nb.sub.1/2]].sub.0.15])[O.sub.3] ceramic.

A study was conducted on the influence of lead vacancies on the R-nFe transition in a Pb(B'1/3B'2/3)O3 compound. The results indicate that both the relaxor behavior and the phase transition are strongly dependent on the lead vacancies content. Moreover, a change in the polar clusters size resulting from lead vacancies formation weakens the dipolar interactions and inhibits the spontaneous relaxor to ferroelectric phase transition.

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]

Lead-free electroceramics samples of composition Ba1−xEr2x/3(Ti1−yZry)O3 (BETZ) with x = 0.01 and 0.02 and 0.20 ≤ y ≤ 0.35 have been elaborated by solid-state reaction technique. X-ray diffraction at room temperature discloses a single perovskite phase with a cubic symmetry. Dielectric measurements were carried out in the ranges (80-445 K) and (102-106 Hz) of temperature and frequencies respectively. The ceramics exhibited normal and/or relaxor ferroelectric properties then some of them have very interesting dielectric characteristics in the vicinity of room temperature. A wide dielectric anomaly combined to the dielectric maxima shift toward a higher temperature with increasing frequency denotes either a diffuse phase transition or relaxor behavior in some ceramics. For any erbium concentration, when titanium is substituted by zirconium, the temperature of the permittivity maximum TC (Tm) and the maximum permittivity (ε′rmax) decreases while ΔTm(f)= [Tm(106 Hz) − Tm(102 Hz)] and tan δ increase. The diffuse phase transition parameters were calculated from the modified Curie-Weiss law linear fit. Further a relaxor nature was confirmed and endorsed by a good fit to the Vogel-Fülcher relation. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous ethyl cellulose exhibits three secondary relaxations at temperatures below its glass transition. The fitted parameters that describe these processes and the comparison with other polysaccharides allow to ascribe the relaxations to lateral groups on one hand and to local main chain motion on the other hand. Their contributions to the dielectric constant overlap and induce a broad dielectric losses peak. The amplitude of one of these relaxations is found to decrease regularly with time. It is believed it comes from a gradual change of the polar groups chemical environment that constrains their motion. [Copyright &y& Elsevier]

Abstract: The BaTi0.4(Fe0.5Nb0.5)0.6O3 ceramic is synthesized by a solid-state reaction technique. The X-ray diffraction of the sample at room temperature shows a cubic phase. The dielectric properties are investigated as a function of frequency (20–106 Hz) at different temperatures (80–417K). A giant low frequency dielectric permittivity () was obtained. Two dielectric relaxation peaks were observed on the curve of dielectric loss vs. temperature. The intrinsic dielectric permittivity calculated by impedance spectroscopy from the values of the obtained bulk capacitances were remarkably high 230<<330. The extrinsic factors play an important role on their dielectric response giving rise to a giant dielectric permittivity at T>150K. The heterogeneities conduction in the grains, grain boundaries and interfacial layers are related to a Maxwell–Wagner relaxation. [Copyright &y& Elsevier]

Abstract: Recently, the concept of polarons has again been at the focus of solid-state research, as it can constitute the basis for understanding the high-temperature superconductivity or the colossal magnetoresistance of materials. More than a decade ago there were some indications that polarons play an important role in explaining low temperature maxima in imaginary part of the dielectric constant in ABO3 perovskites. In the present work we report the ac electrical conductivities of KTaO3; Li and PbTiO3; La, Cu and their frequency and temperature dependence. The real part of the complex ac conductivity was found to follow the universal dielectric response . A detailed theoretical analysis of the temperature dependence of the parameter s revealed that, at low temperatures, the tunnelling of small polarons is the dominating charge transport mechanism in ABO3 perovskites. [Copyright &y& Elsevier]

Pure and well-crystallized Barium Strontium Titanate (BST) nanoparticles with controlled Ba/Sr ratio have been successfully synthesized under supercritical conditions using a continuous-flow reactor in the temperature range of 150-380 degrees C at 26 MPa. To synthesize the Ba0.6Sr0.4TiO3 composition, alkoxides, ethanol and water were used. The resulting nanopowder consists of fine particles with an average particle size of 23 nm. The results show that the Ba/Sr ratio of this powder can be accurately controlled from the composition of precursor. The characterization of the as-synthesized Ba0.6Sr0.4TiO3 solid-solution and the dielectric properties of the sintered ceramics are here reported.