Search results for "Ferro"
showing 10 items of 2451 documents
Crystal chemical and dielectric properties of Pb0.5(5-x)LaxNb5-xFexO15system with “tetragonal tungsten bronze” structural type
2005
The lanthanum-lead and iron-niobium coupled substitution in PbNb 2 O 6 have allowed to isolate new materials of a general formula Pb 0.5(5-x) La x Nb 5-x Fe x O 15 crystallising with the tetragonal tungsten bronze structural type. The resulting influence on the lattice parameters, the ferroelectric Curie temperature and Cole - Cole plots are presented. A typical ferroelectric - paraelectric behaviour occurs in the composition range 0 ≤ x ≤ 0.33 while, a relaxor behaviour is observed in the composition range 0.33 < x < 1.
New ferroelectric materials on the basis of PbSc1/2Nb1/2O3–PbLu1/2Nb1/2O3 solid solutions
2004
Abstract Original binary solid solutions PbSc 1/2 Nb 1/2 O 3 –PbLu 1/2 Nb 1/2 O 3 (PSN-PLuN) have been produced. First of all nominally pure PSN and PLuN were synthesized by solid state reaction from oxides and carbonates. These compounds were mixed in different proportions to obtain (1− x )PSN− x PLuN solid solutions. Ceramic samples were hot-pressed at gradual change of the temperature. Solid solutions have the perovskite structure and are completely soluble in each other. Differential thermal analysis and X-ray diffraction were used to examine the synthesis and phase constitution. Dielectric properties—dielectric permittivity e and dielectric loss tan δ of ceramic samples of originally s…
Ferroelectricity and piezoelectricity in soft biological tissue: Porcine aortic walls revisited
2017
Recently reported piezoresponse force microscopy (PFM) measurements have proposed that porcine aortic walls are ferroelectric. This finding may have great implications for understanding biophysical properties of cardiovascular diseases such as arteriosclerosis. However, the complex anatomical structure of the aortic wall with different extracellular matrices appears unlikely to be ferroelectric. The reason is that a prerequisite for ferroelectricity, which is the spontaneous switching of the polarization, is a polar crystal structure of the material. Although the PFM measurements were performed locally, the phase-voltage hysteresis loops could be reproduced at different positions on the tis…
Radio and Microwave Spectroscopy of 0.2PMN-0.4PSN-0.4PZN Relaxor Ceramics
2005
Dielectric spectroscopy results of 0.2PbMg 1/3 Nb 2/3 O 3 -0.4PbSc 1/2 Nb 1/2 O 3 -0.4PbZn 1/3 Nb 2/3 O 3 ceramics are reported for 200 < T < 450 K and 20 Hz < v < 11 GHz. Dielectric constant is very high (more than 12000) in the vicinity of the peak. Anomalous broad dielectric relaxation has been observed near and below the temperature of the maximum permittivity, T m (at 1 kHz). The distribution of relaxation times have been calculated directly from the dielectric spectra. At higher temperatures than the maximum permittivity, T m the distribution of the relaxation times is symmetrically shaped (Cole-Cole function satisfactory describes the dielectric response). At lower temperatures, the …
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.