Search results for "Kite"
showing 10 items of 1123 documents
Dielectric response of disordered BaBi2Nb2O9perovskite ceramics
2007
Studies of dielectric properties of BaBi2Nb2O9 ceramics are reported. Considerable dispersion of ?* at low- and infra-low frequencies has been revealed in the region of the diffused phase transition. Dispersion of ?* is divided into ''low-temperature'' dispersion related to relaxation of polar formations and their boundaries and ''high-temperature'' dispersion (at T ? Tm) the main contribution to which comes from Maxwell-Wagner relaxation.
Compositional Evolution of Properties in Epitaxial Films of Relaxor PbMg1/3Nb2/3O3-PbTiO3
2005
Epitaxial heterostructures of relaxor (1− x) PbMg1/3Nb2/3O3−(x) PbTiO3 thin films with La0.5Sr0.5CoO3 bottom electrodes were grown by pulsed laser ablation on MgO substrates. Perovskite films with x = 0–0.32 were deposited using sub-monolayer mixing from two targets. Both the room-temperature studies of microstructure and studies of dielectric response as a function of frequency and temperature were performed. For all x, a relaxor-like behavior was observed. The compositional evolution of lattice parameter, permittivity, and temperature of dielectric maxima T m was in a qualitative agreement with that in bulk. The relatively low temperatures T m in the presence of an in-plane compression we…
Dipolar Glass-Like Perovskite Sr0.8Bi0.2TiO3Ceramic
2010
In this work lead-free Sr0.8Bi0.2TiO3 ceramic have been investigated in the frequency range from 20 Hz to 36 GHz. The obtained results show pronounced dispersion below room temperature. It looks more similar to the one observed in dipolar glasses as in relaxors. Calculated relaxation time distribution function broadens towards longest relaxation times with decreasing temperature. The obtained most probable relaxation time fulfills Vogel-Fulcher relationship with the following parameters: dipole activation energy EA/kB = 1718 K, freezing temperature T0 = 65 K, attempt relaxation time, referring to dipole relaxation at very high temperatures, τ0 = 5.5·10−14 s.
Effect of Electromechanical Loading on the Dielectric Properties of PLZT−x/65/35 Ceramics (x = 8 and 8.5)
2011
The influence of uniaxial pressure (0-800 bars) applied parallel to the ac electric field on the dielectric properties of La−modified lead–zirconate−titanate ceramics with the Zr/Ti ratio of 65/35 was investigated. Applying uniaxial pressure leads to the reduction of the peak intensity of the electric permittivity (ϵ), of the frequency dispersion as well as of the dielectric hysteresis. The peak intensity of ϵ becomes diffuse and shifts with increasing the pressure. Our results show that applying uniaxial pressure induces similar effects as increasing the Ti−ion concentration in PZT system. We interpreted our results based on domain switching processes under the action of combined electrome…
PLZTx/65/35 ceramics (x = 2 and 4) under electromechanical and temperature loading
2010
The effect of uniaxial pressure (0–1000 bars) applied parallel to the ac electric field on dielectric properties of La-modified lead–zirconate–titanate, Pb(Ti,Zr)O3 (PZT), ceramics with Zr/Ti ratio of 65/35 was investigated. The experimental results revealed that applying uniaxial pressure leads to a reduction of the peak intensity of the electric permittivity (e), of the frequency dispersion as well as of the dielectric hysteresis. Moreover, with increasing pressure, the peak intensity of e becomes diffuse and shifts to a higher temperature. It was concluded that applying uniaxial pressure induces similar effects as increasing the Ti–ion concentration in PZT system. The obtained results we…
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…
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…
SrTiO3and Pr Effects on Structural, Dielectric and Ferroelectric Properties of Na0.5Bi0.5TiO3Ceramic
2015
[(Na0.5Bi0.5TiO3)0.7Sr0.3]1-xPrxTiO3(NBTS30P) (0 ≤ x ≤ 0.025) ceramics were prepared by solid-state synthesis process. Their crystal structure, microstructure dielectric and ferroelectric properties were studied. XRD data show that all of the ceramics possess a single perovskite phase. SEM results confirm that the ceramics are well sintered and exhibit relative densities higher than 97%. The results also reveal that the microstructure of the different compositions do not show a significant variation. The praseodymium (Pr) substitution to NBTS30 results in a change of crystal structure from cubic to tetragonal at x = 0.025. At the same time, electric permittivity decreases, the maximum is br…