Temperature Of Permittivity Maximum Research Articles

Influence of Grain boundary Layers on the Dielectric Relaxation of Nb-Doped SrTiO3

The dielectric relaxation of Nb-doped SrTiO3 in the temperature range of 500–900 K was investigated to understand the effect of space charge in grain boundary layers. The dielectric relaxation phenomena were observed for all specimens, regardless of the doping content of Nb. The permittivity maximum temperature (Tεm) shifted and the permittivity peak height varied with the doped content of Nb. In order to study the effect of space charge in the grain boundary on the dielectric relaxation, Bi ions were diffused along the grain boundary of a 0.6 mol% Nb-doped SrTiO3 specimen. It was found that the dielectric relaxation behavior changes with the diffusion of Bi. These relaxations can be explained in terms of the space charge, which is varied by defects, in grain boundary layers.

Dielectric properties of cobalt and chromium doped lead iron tungstate relaxor ceramics

The effect of Co and Cr doping on the dielectric properties of Pb(Fe2/3 W1/3)O3 relaxor ceramics is analysed in this work. No second phases were detected for Co doped PFW for Co < 7.5 at%. On the other hand, a Pb2WO5 second phase was identified in Cr doped PFW. Both Co and Cr decrease the permittivity maximum and shift transition temperature to high temperatures. Relaxor aging behaviour was observed for both doped compositions, being more pronounced for Cr doped PFW. Oxygen annealing post-sintering treatment increases εrmax and the sharpening of temperature dielectric response of Cr doped PFW. The observed dielectric modifications are discussed in relation to the probable defects present in the ceramics

Phase transitions due to polar region structure in disordered ferroelectrics

We show clear experimental evidence for two phase transitions in titanium doped lead magnesium niobate compositional disordered ferroelectrics. One is the diffuse phase transition near the temperature of the dielectric permittivity maximum, which is often called the characteristic of relaxor ferroelectrics (relaxors). Another is a first-order transformation from relaxor ferroelectric to normal ferroelectric, corresponding to a zero-field spontaneous polar micro-macrodomain switching. According to X-ray diffraction (XRD) measurements, thermal analysis and transmission electron microscope (TEM) results, a dynamic behavior of polar microregions is necessary to explain the phenomena, which is more similar to a stress induced martensitic transformations form cubically stabilized perovskite parent-phase. It is also observed that the dynamic behavior of polar regions was influenced by the titanium doping.

The variation of phase transition behavior on substituting Pb2+ and Sr2+ for a site cations in (Na1/2Bi1/2)TiO3 system

The phase transition behavior in (Na1/2Bi1/2)1-xPbxTiO3[NBPT(x)] and (Na1/2Bi1/2)1-xSrxTiO3[NBST(x)] with respect to changes in composition and temperature was investigated using X-ray analysis and dielectric characterization. Morphotropic phase boundary(MPB) are located in the composition range of 0.13 < × < 0.15 and 0.25 < × < 0.26 in NBPT(x) and NBST(x), respectively. The phase transition exhibited more 1st order behavior and the dielectric loss could be suppressed at high temperatures with the increase of Pb2+ substitutions. NBST(x) showed diffuse phase transition and the degree of the shift in permittivity peak with the measuring frequency increased with the increase of SrTiO3 content. This increase was correlated with the symmetry at room temperature and decrease of the temperature of maximum permittivity

Effects of a bias on the permittivity of PLZT 9/65/35

We have measured the low-field dielectric response, , in the relaxor with x = 0.09 and y = 0.65 (PLZT 9/65/35) subjected to an external field E varying linearly in the range. In the experimental temperature domain, we point out two regimes of -variations, which are attributed to electromechanical coupling: electrostriction at high temperature and domain wall motions at low temperatures. The cross-over is found close to , the temperature of permittivity maximum in the zero-field condition (E = 0). It is proposed that the external field induces metastable long-range ordering correlations, leading to the observed time-dependent effects. An exponent related to the distribution of relaxation time has been determined through a non-Debye relaxation analysis.

Effects of surface layers on the physical properties of lanthanum doped lead zirconate titanate ceramic

Dielectric measurements in the temperature range of -20°C to 160°C have been performed on lanthanum doped lead zirconate titanate ceramic samples with rough ground, polished and chemically etched surfaces. It is found that the dielectric constants, dielectric loss, polarization and pyroelectric coefficient are the smallest in the ground samples and the largest in the etched samples. The difference is very pronounced near the permittivity maximum temperature Tmax. The measured dielectric constant was found to depend on sample thickness in the ground and polished samples but not in samples with etched surfaces. The results are explained in terms of a simple surface layer model. A nonferroelectric layer is produced during lapping, which has a dielectric constant of the order of 100 and the capacitance of this layer in the investigated temperature range is 0.2-0.7 μF/cm2. Through post-annealing, the contributions from the nonferroelectric nature of this surface layer and from the two dimensional tensile stres...

Effects of pressure, DC-electric field and frequency on the dielectric properties of lead indium niobate

Abstract The pressure (0–6kbar), DC-bias field(0–11kV/cm) and frequency(300Hz–100kHz) dependence of dielectric properties of PIN ceramics prepared by different thermal processing techniques (conventional method:sample A and fast firing;sample B) were reported. PIN sample A reveals coexistence of a ferroelectric relaxor (disordered state) and an antiferroelectric phase(ordered one), while sample B reveals a ferroelectric relaxor. For sample A, the permittivity maximum(erm′ =1800 at 1kHz) temperature Tm decreases with pressure(dTm/dp=−2°C/kbar) and antiferroelectric transition temperature Tt increases with p(dTt/dp=5°C/kbar). For sample B(with e rm′ = 3500 at 1kHz), the Tm decreases with dTm/dp=−3°C/kbar, and a remarkable decrease in e rm′ with DC-bias field and a strong dielectric relaxation of polydispersive type which obeys the Cole-Cole arc law were observed.