Dielectric Temperature Curve Research Articles

Effect of Different Ca2+ and Zr4+ Contents on Microstructure and Electrical Properties of (Ba,Ca)(Zr,Ti)O3 Lead-Free Piezoelectric Ceramics

In the preparation of (Ba,Ca)(Zr,Ti)O3 lead-free piezoelectric ceramics, different Ca2+ and Zr4+ contents will greatly affect the phase structure, microstructure, and electrical properties of the ceramics. XRD shows that all samples have pure perovskite phase structure, and the (Ba0.85Ca0.15)(ZryTi1−y)O3 ceramics morphotropic phase boundary region from tetragonal phase to rhombohedral phase near 0.08 ≤ y ≤ 0.1. From the dielectric temperature curve, the phase transition temperature (TO-T) was found near room temperature at 0.12 ≤ x ≤ 0.18 for the (Ba1−xCax)(Zr0.1Ti0.9)O3 ceramics. Both Ca2+ and Zr4+ increase have a significant decrease on the Curie temperature Tc. All samples were revealed as relaxers with diffusivities in the range 1.29 ≤ γ ≤ 1.82. Different from the undoped ceramics, ceramics doped with Ca and Zr ions exhibit saturated P–E hysteresis loops, and their ferroelectric properties are significantly optimized. In particular, the (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramic demonstrated optimal properties, namely d33 = 330 pC/N, kp = 0.41, εr = 4069, Pr = 4.8 μC/cm2, and Ec = 3.1 kV/cm, indicating that it is a viable lead-free piezoelectric contender. Variations in Ca and Zr content have a significant effect on the crystal grain sizes and densities of ceramics, which is strongly associated with their piezoelectricity.

Construction of lead-free dielectrics for high temperature multilayer ceramic capacitors and its inner electrode matching characteristics

High-temperature multilayer ceramic capacitors (HT-MLCCs) are indispensable key basic components in high-temperature electronic equipment. Obtaining practical HT-MLCCs requires not only a high-temperature dielectric with excellent temperature stability, but also a good match between the inner electrode and the dielectric. In this work, a quaternary lead-free system (1-x) (0.64Na0.5Bi0.5TiO3-0.16 K0.5Bi0.5TiO3-0.20Bi(Mg2/3Nb1/3)O3)-xCaZrO3 (NBT-KBT-BMN-xCZ) was investigated as candidates for high-temperature dielectric. The introduction of CZ can adjust the composition of different types of polar nanoregions (PNRs) and weaken the ferroelectric coupling behavior, thereby achieving the flattening of the dielectric temperature curve. Among all the components, NBT-KBT-BMN-0.06CZ (0.06CZ) has the most excellent high-temperature dielectric properties, and is further used to match the two inner electrodes of Pt and Ag/Pd to make HT-MLCCs. The results show that for Pt-MLCC, co-firing causes a second phase MgTi2O5 to appear at the heterogeneous interface, resulting in incomplete inner electrodes, lower dielectric permittivity and increased loss in the high-temperature region. In contrast, for Ag/Pd-MLCC, the heterogeneous interface is well bonded, the inner electrode is continuous and complete and there is no second phase, which makes the capacitor show excellent dielectric performance (εr=1393±15%, tanδ≤0.025) over a wide range of 129–404 °C. This work provides an important solution for the development of a new generation of HT-MLCCs.

Electric property, anti-reduction mechanism of (1 − x)BaTiO3–xBiCoO3–Mn ceramics

0.5wt%MnO2-doped (1 − x)BaTiO3–xBiCoO3 ceramics short as (1 − x)BT–xBC–M sintered in air and reducing atmosphere via solid-state process were investigated. The X-ray diffraction results showed that solid solubility in (1 − x)BT–xBC ceramics sintered in the air was higher than that in reducing atmosphere. (1 − x)BT–xBC–M ceramics sintered in air transformed from tetragonal to pseudo-cubic phase when x ≥ 0.1. The scanning electron microscopy results indicated that the average grain size increased with the BC component increasing; however, opposite phenomena occurred in samples sintered in the reducing atmosphere. The dielectric temperature curves of samples sintered in reducing atmosphere were flatted with excellent insulation resistivity of an order of magnitude of 1013 Ω·cm, while anomalous dielectric constant and dielectric loss of samples sintered in the air with deteriorated insulation resistivity of an order of magnitude of 107 Ω·cm. The anti-reduction mechanism of (1 − x)BT–xBC–M system was explained by the “electron–hole” trapping effect and formation of defect dipoles $$\left[ {{\text{Mn}}_{{{\text{Ti}}}} ^{{\prime \prime }} - V_{{\text{O}}}^{{ \cdot \cdot }} } \right]$$ and $$\left[ {2{\text{Co}}_{{{\text{Ti}}}} ^{\prime } - V_{{\text{O}}}^{{ \cdot \cdot }} } \right]$$ .

Effect of SiO2/B2O3 Ratio on the Crystallization Behavior and Dielectric Properties of Barium Strontium Titanate Glass–Ceramics Prepared by Sol–Gel Process

Ferroelectric glass–ceramics, with a basic composition 90 wt.% (Ba0.65Sr0.35)TiO3−10 wt.% (B2O3−nSiO2) (n = 0.5, 1, 3, 5) were synthesized by the sol–gel method and their phase development and dielectric properties were investigated by differential thermal analysis, x-ray diffraction, field emission scanning electron microscopy, dielectric temperature curves and impedance spectroscopy. From the differential thermal analysis, glass transition and crystallization behavior can be observed. From the x-ray diffraction study, two crystalline phases (Ba,Sr)TiO3 and Ba2TiSi2O8 were formed over the entire composition range of the glass–ceramics. In addition, the main crystal phase has undergone a transformation from (Ba,Sr)TiO3 to Ba2TiSi2O8 with the increase of n. A typical structure in which the crystal phase was surrounded by a glassy matrix has been observed in the scanning electron microscope images. As a result of temperature dependent dielectric property measurements, the dielectric constant increased obviously with the increase of n from 0.5 to 1. Further increasing n led to a reduction of the dielectric constant, which is in coincidence with the variation of the intensity of (Ba,Sr)TiO3 phase with n. According to the impedance spectroscopy analysis and the activation energy calculation, the relaxation peak in both Z″ and M″ data should be attributed to the crystal–glass interface, and the change of conduction mechanism with the increase of SiO2/B2O3 ratio may be attributed to the corresponding transition of the main crystal phase.

The Dependence of Dielectric and Ferroelectric Properties on Crystal Phase Structures of the Hydrogenized P(VDF-TrFE) Films With Different Thermal Processing.

Different thermal treatments were used to obtain various crystal structures of hydrogenated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] films synthesized by an atom transfer radical chain transfer and controllable elimination reaction route. After analyzing the results of X-ray diffraction and differential scanning calorimeter, we found that these P(VDF-TrFE) samples possessed mixed crystal phases of α , β , and γ with various compositions depending on the TrFE content and processing temperature, and this characteristic was also demonstrated by the dielectric temperature curves. After polarizing the P(VDF-TrFE) samples at different electric fields, the effect of crystal structure on their ferroelectric and piezoelectric properties was illustrated and conformed by field emission scanning electronic microscopy morphology, which was found that large TrFE content and high temperature processing were responsible for the large remnant polarization. As a result, the annealed P(VDF-TrFE) 80/20 mol% possessed a high remnant polarization of [Formula: see text]/cm2, a large piezoelectric value ( d33 = -25 pC/N), and a favorable electromechanical coupling factor ( kt = 0.26 ), providing a reliable method for the structure design and sample fabrication of this kind of copolymer aimed at the applications in piezoelectric sensors and actuators.

Interfacial polarization arising from two contributions in glass added barium titanate ceramics

The glass added barium titanate ceramics were prepared and their dielectric properties have been investigated as a function of temperature, frequency, bias voltage, and specimen thickness. The XRD result indicated that the specimen exhibits a single perovskite structure without any detectable secondary phases. And microstructural observation showed that the average grain size was about 1 μm and there was no apparent abnormal grain growth. In addition, the dielectric temperature curve revealed an extremely high dielectric peak with strong frequency dispersion. The bias voltage dependence of the impedance and modulus spectra demonstrated that this increase in dielectric permittivity in the ferroelectric regime was related to the interfacial polarization at both the electrode/ceramic and the grain/glass interfaces. Moreover, the remarkable thickness dependence of dielectric response demonstrated the existence of the interfacial polarization at the electrode/ceramic interfaces. The two deduced contributions to the interfacial polarization were qualitatively discussed to complement the proposed formation mechanism.

Two dielectric relaxation mechanisms observed in lanthanum doped barium strontium titanate glass ceramics

The dielectric relaxation at temperatures ranging from 100 °C to 550 °C in lanthanum-doped barium strontium titanate glass ceramics has been investigated by measurements of both dielectric temperature curve and complex impedance spectroscopy. The temperature dependence of dielectric properties reveals two regimes. In the first regime, at temperatures lower than 350 °C, the charge carrier contributed to interfacial polarization is conduction electrons. In contrast, in the second regime, at temperatures higher than 350 °C, the dielectric relaxation was attributed to the thermally activated movement of oxygen vacancies. Thus, two relaxation mechanisms could be explained on the basis of defect chemistry and impedance analysis.

Studies of Ferroelectric and Dielectric Properties of Samarium Doped Barium Titanate Sintered in Pure Nitrogen

This paper investigated the ferroelectric and dielectric properties of Sm-doped BaTiO3 sintered in different atmosphere. The influence of variable doping concentration on microstructure, ferroelectric and dielectric properties was studied. The results showed that the dielectric-temperature curve of Sm-doped BaTiO3 was smoother than that of pure BaTiO3. And tunability of Sm-doped BaTiO3 was smaller than that of pure BaTiO3. Dielectric constant of the samples sintered in nitrogen was smaller than that of samples sintered in air. The hysteresis loop displayed that ferroelectric polarization decreased with Sm doping.

Development of non-stoichiometric SrBi4+2xTi4O15+3x (−0·04 ≤x≤ 0·04) ceramics

The non-stoichiometric compositions of Bi layered structural SrBi4Ti4O15 ferroelectric materials (SrBi4+2xTi4O15+3x, x=−0·04, −0·02, 0, 0·02 and 0·04) are investigated as the main precursors to find the influence of Bi2O3 content on the characteristics of SrBi4Ti4O15 ceramics. The effect of compositional variation on the sintering and the dielectric characteristics of SrBi4Ti4O15 ceramics are deduced with the aid of X-ray diffraction patterns, scanning electron microscopy observation and dielectric–temperature curves. From the scanning electron microscopy observations, the SrBi3·92Ti4O14·88 and SrBi3·96Ti4O14·94 ceramics reveal two phased grain growth, bar typed and irregularly disc typed grains coexist; the other SrBi4+2xTi4O15+3x ceramics reveal irregularly disc typed grains. From the X-ray patterns, the Bi2Ti2O7 and SrTiO3 phases are observed in the SrBi3·92Ti4O14·88 and SrBi3·96Ti4O14·94 ceramics. Except the SrBi3·96Ti4O14·94 ceramics, the other SrBi4+2xTi4O15+3x ceramics have revealed a splitting peak in the (119) plane. It is also shown that the compositional variation has apparent influences on the grain morphologies, the bulk densities, the Curie temperatures and the maximum dielectric constants of SrBi4+2xTi4O15+3x ceramics.

The influence of different fabrication processes on characteristics of excess Bi 2O 3-doped 0.95 (Na 0.5Bi 0.5)TiO 3–0.05 BaTiO 3 ceramics

In this study, we will develop the influences of the excess x wt% ( x=0, 1, 2, and 3) Bi 2O 3-doped and the different fabricating process on the sintering and dielectric characteristics of 0.95 (Na 0.5Bi 0.5)TiO 3–0.05 BaTiO 3 ferroelectric ceramics with the aid of SEM and X-ray diffraction patterns, and dielectric–temperature curves. The 0.95 (Na 0.5Bi 0.5)TiO 3–0.05 BaTiO 3+ x wt% Bi 2O 3 ceramics are fabricated by two different processes. The first process is that (Na 0.5Bi 0.5)TiO 3 composition is calcined at 850 °C and BaTiO 3 composition is calcined at 1100 °C, then the calcined (Na 0.5Bi 0.5)TiO 3 and BaTiO 3 powders are mixed in according to 0.95 (Na 0.5Bi 0.5)TiO 3–0.05 BaTiO 3+ x wt% Bi 2O 3 compositions. The second process is that the raw materials are mixed in accordance to the 0.95 (Na 0.5Bi 0.5)TiO 3–0.05 BaTiO 3+ x wt% Bi 2O 3 compositions and then calcining at 900 °C. The sintering process is carried out in air for 2 h from 1120 to 1240 °C. After sintering, the effects of process parameters on the dielectric characteristics will be developed by the dielectric–temperature curves. Dielectric–temperature properties are also investigated at the temperatures of 30–350 °C and at the frequencies of 10 kHz–1 MHz.

Dielectric materials based on superimposed effect

The dielectric properties and phase compositions of two kinds of SrTiO3-PbTiO3-Bi2O3. nTiO2-system ceramics, sintered with different Sr/Pb ratio, are investigated. The result shows that the ceramics, with inhomogeneous distribution of the two different systems, will present two-phase mixed structure. It will result in the superimposing effect in dielectric property as well as the double-hump characteristic in dielectric-temperature curve. Ceramic materials with high dielectric constant, low loss and low temperature variation rate can be obtained through regulating the Sr/Pb ratio within each system and the use level between two systems, and through controlling sintering temperature and the heat preservation time.