Search results for "ELECTRICITY"
showing 10 items of 1225 documents
Influence of Compressive Stress on Dielectric and Ferroelectric Properties of the 0.9PbSc0.5Nb0.5O3-0.1PbLu0.5Nb0.5O3Ceramics
2014
0.9PbSc0.5Nb0.5O3-0.1PbLu0.5Nb0.5O3ceramics were prepared by a solid-state mixed-oxide technique. The phase formation and microstructure were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The influences of compressive stress (0 – 1500 bar) applied parallel to the electric field on the dielectric and ferroelectric properties of these ceramics were investigated. The results showed that the compressive stress had pronounced effects on these properties. With increasing pressure, the electric permittivity maximum decreases and shifts to higher temperature, thermal hysteresis, dielectric dispersion and polarization decrease. The obtained results were …
Pulsed laser deposition of relaxor ferroelectric films
1998
Heterostructures of perovskite relaxor ferroelectric (RFE) thin films onto La 0.5 Sr 0.5 CoO bottom electrode layers were grown by pulsed laser deposition on MgO(100) crystal substrates. The films were highly oriented, with (h00) planes parallel to the substrate surface, and demonstrated good dielectric and ferroelectric quality at room temperature. The studies of the dielectric properties of the films over the frequency range of 20 Hz....100 kHz and over the temperature range of 0...350°C revealed relaxor type behavior in the films. A diffuse ferroelectric phase transition and a shift of the maximum dielectric permittivity towards higher temperatures with increasing frequency were observed…
Semi-empirical indo and shell-model calculations for perovskites
1999
Abstract Structural, phonon and some elastic and dielectric properties have been calculated for various paraelectric or ferroelectric phases of the perovskites KNbO3 and SrTiO3, using either the semi-empirical INDO (Intermediate Neglect of Differential Overlap) method or a temperature-dependent shell model. The INDO method was used to calculate the energy changes resulting from [100], [110] or [111] displacements of Nb atoms in the cubic perovskite cell of KNbO3, at 0K. The conventional shell model gives a good account of the elastic, dielectric and phonon properties of the cubic phase of strontium titanate at room temperature, but difficulties remain in modelling the permittivity and elast…
Dielectric Permittivity and Conductivity of Li0.07Na0.93Ta0.1Nb0.9O3and Li0.07Na0.93Ta0.111Nb0.889O3Solid Solutions
2011
Results of studies of dielectric properties and conductivity in 290–700 K range of temperature and frequencies from 25 to 106 Hz in ferroelectric perovskite solid solutions Li0.07Na0.93Ta0.1Nb0.9 O3 and Li0.07Na0.93Ta0.111Nb0.889 O3 are reported. A first-order ferroelectric phase transition proceeds in both studied compositions within the observed range of temperature. The co-precipitated Ta2yNb2(1-y)O5 pentoxides being used for synthesis of Li0.07Na0.93Ta0.111Nb0.889O3 the Curie point shifts by ∼75 K to a lower temperature while compared with Li0.07Na0.93Ta0.1Nb0.9O3 synthesised from mechanical mixture of the Ta2O5 and Nb2O5 oxides the high-frequency dielectric permittivity and ion conduct…
Structural and Dielectric Properties of (Na0.5Bi0.5)0.70Ba0.30TiO3 Ceramics.
2003
Abstract A (Na0.5Bi0.5)0.70Ba0.30TiO3 ceramic has been studied by X-ray diffraction and by measurements of dielectric and ferroelectric properties between room temperature and 450 °C. A sharp increase in the electric permittivity and dielectric loss near 200 °C has been observed. This sharp increase in dielectric responses indicates a transformation between normal and relaxor ferroelectric states. It is found that polar regions can exist at higher temperatures. The X-ray diffraction study shows that the transformation corresponds to the first order phase transition from tetragonal to cubic. The use of the (Na0.5Bi0.5)0.70Ba0.30TiO3 ceramic for device application has also been indicated.
The Nature of Dielectric Nonlinearity in the Region of Diffused Phase Transition in Layered Ferroelectric BaBi2Nb2O9
2008
By studying the dielectric properties of BaBi 2 Nb 2 O 9 ceramics, a representative of layered ferroelectrics, significant dispersion of ϵ* has been revealed at low- and infra-low frequences in the region of phase transition. Dispersion of ϵ* observed in “low-temperature” region (T T m where the basic contribution to ϵ* is provided by processes of the Maxwell-Wagner relaxation.
Crystal growth and hysteresis phenomena of rubidium tetrachlorozincate Rb2ZnCl4
1988
Abstract Phase transitions in Rb2ZnCl4 crystals grown by various methods are examined with differential scanning calorimetry and dielectric measurements. For most of the studied samples the permittivity along the ferroelectric axis shows a large thermal hysteresis over a wide temperature range including the incommensurate phase and the lock-in point. This hysteresis depends on the presence of different defects which appear during crystal growth or after a thermal and mechanical treatment. It is shown that dielectric measurements are quite well suited to characterize the crystals exhibiting on incommensurate phase and a ferroelectric phase.
Ferroelectric Properties and Crystal Structure of YBa2Cu3O7/BaxSr(1−x)TiO3 Heterostructures
1997
ABSTRACTEpitaxial YBa2Cu3O7/Ba0.5Sr0.5TiO3 (YBCO/BST) and YBCO/BaTiO3 (BTO) heterostructures were prepared by dc and rf sputtering on SrTiO3 and MgO substrates. The YBCO/BTO bilayers exhibit an inductive superconducting transition temperature of 85 K and the ferroelectric phase transition of BST shows a Curie-Weiss temperature of 310 K. Microstructure was investigated by x-ray-diffraction and atomic force microscopy. In this work we also studied the insulator's conductivity and the contribution of domain walls to permittivity.
Sb Effect on Structural, Dielectric, and Ferroelectric Properties of Na0.5K0.5NbO3Ceramics
2015
Lead-free Na0.5K0.5(Nb1-xSbx)O3 (0<x<0.05) ceramics were fabricated by the solid-state reaction method and materials with more than 95% densification were obtained. A microstructure study confirms that the ceramics are well sintered. All compositions show complete perovskite solid solutions. Structural, dielectric and ferroelectric investigations for these specimens were performed. X-ray measurements showed that all compositions have a single perovskite structure with orthorhombic symmetry. Dielectric study revealed that the ceramics obtained are normal ferroelectrics. However some signs of diffuse phase transition were observed. The transition temperatures and the maximum electric permitti…
Uniaxial stress dependence of the dielectric and ferroelectric properties of the Na0.5K0.5NbO3and Na0.5K0.5NbO3 + 0.5 mol%MnO2ceramics
2013
Na0.5K0.5NbO3 and Na0.5K0.5NbO3 + 0.5 mol%MnO2 lead-free ceramics have been produced by solid phase hot pressing sintering process at 1120–1145°C. The results of the X-ray diffraction measurements showed that the obtained samples possessed a perovskite structure. The micrograph of the fractured surface showed a dense ceramic structure, in compliance with 93% relative density determined by the Archimedes method. The dependence of dielectric and ferroelectric properties on the uniaxial compressive stress (0–3000 bar) of the Na0.5K0.5NbO3 and Na0.5K0.5NbO3 + 0.5 mol%MnO2 ceramics was investigated. Significant influence of the external stress on these properties was revealed. It includes a shif…