Microstructure, Dielectric, and Piezoelectric Properties of Pb0.92Ba0.08Nb2O6–0.25 wt% TiO2 Ceramics: Effect of Sintering Temperature

Effects of the doping of W6+ ions on the structure and electrical properties of Pb0.95Ba0.05Nb2O6 piezoelectric ceramics

Microstructure, dielectric and piezoelectric properties of (Pb1−xSrx)Nb1.96Ti0.05O6 ceramics

The effect of sintering temperature on the phase evolution, microstructures, dielectric properties and energy-storage properties of lead lanthanum zirconate titanate antiferroelectric ceramics has been investigated. Scanning electron microscopy images showed that a gradual increase in grain size with increasing sintering temperature. The dielectric measurements revealed that the variation of sintering temperature did not lead to a systematic trend. A correlation between the dielectric properties and microstructures was established. The room temperature dielectric properties demonstrated that both the dielectric constant and saturation polarization increased with increasing sintering temperature up to 1180 °C and then slightly decreased. Furthermore, as for the sintering temperature dependence of energy storage properties, it has shown that with the increase of sintering temperature, both the charged density and discharged density first increased and then decreased. There is an intermediate optimum sintering temperature range (1180 ∼ 1200 °C) in which the samples have better energy storage performance. The dependence of released energy and power densities on the sintering temperature was also investigated. These charge-discharge measurement results were consistent with the calculated values obtained from polarization-electric field hysteresis loops.

0.75BiFeO3-0.25BaTiO3 (75BF-25BT) has been widely concerned because of its lead-free and high Curie temperature. However, the phenomenon of Bi2O3 volatilization and Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> valence change in the sintering process of BF-BT ceramics leads to higher defect ion concentration and dielectric loss tanδ. In order to make it have higher potential in low cost, environmental protection and high temperature piezoelectric applications, researchers used different methods to study 75BF25BT. In this paper, the excellent performance of 75BF-25BT was studied by changing the sintering temperature. Lead free piezoelectric ceramic powders were prepared by traditional solid-state reaction method. After pressing, the samples were sintered at different temperatures (960 °C, 980 °C, 1000 °C, 1020 °C, 1040 °C). XRD analysis shows that all ceramic samples are perovskite structure, and there is no impurity phase. The lattice constant of ceramic samples at different sintering temperatures first increases and then decreases, and reaches the maximum at 1020 °C. At the same time, the relative density of ceramic samples is higher than 94 %, with the highest value of 95.1 % at 1020 °C. Compared with 960 °C, the remnant polarization value Pr is obviously increased, and the highest value is 15.4 C/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 1020 °C. The Curie temperature is inversely correlated with the sintering temperature. With the increase of sintering temperature, the Curie temperature decreases. The highest piezoelectric constant d33, dielectric constant εr, lowest dielectric loss tanδ and Curie temperature Tc are 111 pC/N, 388, 2.3 % and 554 °C respectively at 1020 °C due to the influence of large lattice constant, high relative density and large remnant polarization value. These results show that the optimum sintering temperature is 1020 °C, Bi <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> volatilization is less, defect ion concentration is reduced, and it has excellent electrical properties.

ABSTRACT(Pb0.985-xBi2x/3La0.01)(Nb0.95Ti0.0625)2O6 with 2 wt% excess PbO (x = 0, 0.01, 0.04, 0.06, 0.1) piezoelectric ceramics with high Curie temperature were fabricated via a conventional solid-state reaction method. Dielectric and piezoelectric properties of the ceramics were studied. The Curie temperatures of the ceramics decrease with the increase in the Bi3+ amount. The values of dielectric constant remain nearly unchanged from room temperature up to about 400 °C for the ceramics with x = 0, 0.01, 0.04 and 0.06. The ceramic with x = 0.04 possesses high piezoelectric charge constant (87 pC/N), low mechanical quality factor (22.60), low dielectric loss (0.024), and high Curie temperature (494 °C).

Effects of sintering temperature on microstructure and dielectric properties of Sr0.985Ce0.01TiO3 ceramics

Polycrystalline Ni0.3Cu0.2Zn0.5Fe2O4 and Ni0.3Cu0.2Zn0.5Sc0.05Fe1.95O4 compounds have been prepared by standard solid-state reaction technique and sintered at 1000, 1100, 1150, 1200, and 1250 °C for 5 h in air. The effect of sintering temperature on the structural, morphological, magnetic, dielectric, and electrical properties of these spinel ferrites has been studied thoroughly and comparatively. Formation of the single-phase cubic spinel structure of these compositions is confirmed by X-ray diffraction analysis. The lattice constant increases with sintering temperature as well as with 5% scandium (Sc3+) doping in Ni–Cu–Zn ferrite. Surface morphology reveals that the grain size increases with sintering temperature. Among the prepared ferrites, Ni0.3Cu0.2Zn0.5Sc0.05Fe1.95O4 has the maximum density (5.05 × 103 kg/m3) at sintering temperature 1150 °C, which gives the highest value of initial permeability. It is observed that initial permeability varies with sintering temperature, and it gives the maximum value at optimum sintering temperature. It is noted that Curie temperature decreases with 5% Sc3+ ions doping, whereas it slightly increases with increasing sintering temperature for both compositions. Ni0.3Cu0.2Zn0.5Fe2O4 compound shows the highest Curie temperature 418 °C. Dielectric constant, dielectric loss factor and AC electrical conductivity decrease with 5% Sc3+ ions doping in Ni–Cu–Zn ferrite. The initial permeability decreases sharply at Curie temperature, which indicates a high degree of compositional homogeneity. The ‘Hopkinson’ peak is observed just below the Curie temperature in the real part of initial permeability versus temperature graphs. The mechanism of dielectric polarization and electrical conductivity has been explained based on the electron hopping between Fe3+ and Fe2+ ions. The variation trend of complex impedance and AC electrical conductivity reveals the semiconducting behavior of the ferrite samples. Formation of partial semicircles in the Z/-axis indicates that relaxation process is non-Debye type. The investigated ferrites show relatively high initial permeability, low magnetic loss, and low electrical conductivity in a wide frequency range, which make them potential candidate for various practical applications such as small and compact power suppliers for computers, microprocessors, microwave electronic devices, etc.

Polycrystalline Bi 0.85Eu 0.15FeO 3 ceramics were synthesized by solid-state reaction method with rapid liquid phase sintering process at various sintering temperatures. The dependence of structural, microstructural, electrical, and magnetic properties on sintering temperature was systematically investigated. X-ray diffraction measurements reveal that single perovskite phase is developed in Bi 0.85Eu 0.15FeO 3 ceramics sintered at 850 and 870∘ C, while secondary phases can be detected in the samples sintered at 890∘ C due to the volatilization of Bi 3+ ions, and the crystallinity increases with increasing sintering temperature from 850 to 890 °C. The scanning electron microscopy investigation has suggested that the grain size increases with increasing sintering temperature from 855 to 890∘ C; while the pore size decreases with increasing sintering temperature from 850 to 870∘ C and then increases with a further increase of sintering temperature. The electrical and magnetic measurements show that the leakage current, dielectric constant, dielectric loss, and magnetic properties are strongly dependent on the sintering temperature. The Bi 0.85Eu 0.15FeO 3 ceramics sintered at 870∘ C have the lower leakage current, higher dielectric constant, and lower dielectric loss. The room temperature magnetization increases with increasing sintering temperature from 850 to 890 °C. The possible reason for all the above observations was discussed.

Achieving broad absorption bandwidth of Ba2Co2Fe12O22 ferrites by adjusting the sintering temperature

Enhanced dielectric and piezoelectric properties in Li/Sb-modified (Na, K)NbO3 ceramics by optimizing sintering temperature

Barium strontium titanate is an important electronic functional ceramics, which has a strong dielectric nonlinearity and excellent ferroelectricity. In the present study Ba0.7Sr0.3TiO3 ceramics were synthesized by conventional solid state reaction method. The effects of sintering temperature on the microstructure, dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 ceramics have been investigated. The XRD results show that Ba0.7Sr0.3TiO3 ceramics sintered at 1350–1450 °C were single tetragonal phase. The lattice constant and tetragonality decreased as sintering temperature increasing. The grain size increased with the rise of sintering temperature. The dielectric properties of Ba0.7Sr0.3TiO3 ceramics sintered at 1350 °C were superior to that of the ceramic samples sintered at 1400 and 1450 °C. The decrease of tetragonality with the rise of sintering temperature leaded to the fall of the Curie temperature of Ba0.7Sr0.3TiO3 ceramics. Ba0.7Sr0.3TiO3 ceramics sintered at 1350–1450 °C were relaxor ferroelectrics. The diffuseness weakened as sintering temperature increase. The remnant polarization and coercive field gradually increased with the rise of sintering temperature.

Synthesis and properties of Pb(Co1/3Nb2/3)O3 ceramics

In this study, the physical properties, dielectric properties, and micro-hardness of (Ba0.90Ca0.10)0.90(Na0.50Bi0.50)0.10TiO3 or BCT-NBT ceramics prepared by molten salt method with various sintering temperatures were investigated. The powders were calcined at 500-1100°C for 4 h with heating rate of 5°C/min. It was found that the optimum calcination condition was 1000°C for 4 h. These powders were pressed and sintered at 1200-1400°C for 3 h with a heating rate of 5°C/min. The microstructure was examined by scanning electron microscope (SEM). The density of the sintered samples was measured by Archimedes method with distilled water as the fluid medium. Dielectric properties were examined by LCR meter. The micro-hardness of the BCT-NBT ceramics was determined using the Vickers and Knoop indentation techniques. The results showed that the average grain sizes increased with increasing sintering temperatures. At sintering temperatures higher than 1200°C, the fracture mode changed from partial intra-granular to mainly intra-granular. The sintering temperature at which the density, dielectric and hardness properties were maximal was 1350°C. The highest density was about 5.4 g/cm3, and the Vickers and Knoop micro-hardnesses were 6.6 and 6.4 GPa, respectively. The dielectric constant at the Curie temperature was 3682 and the dielectric loss was 0.01 at 1 kHz frequency.

Al2O3 ceramics doped with 15%Nb2O5 and 7.5%La2O3 (volume percent) were prepared by microwave sintering at 1450~1550°C for 30min. The effect of sintering temperature on the microstructure, especially Al2O3 columnar grains, and the fracture toughness were investigated. The results show that the phases of sintered samples were α-Al2O3, LaNbO4 and Nb2O5, without La2O3. During the sintering period, the in-situ reacted LaNbO4, and the remained Nb2O5 after reacting, changed to liquid which promoted the growth of Al2O3 columnar grains and sintering densification. With the increase of sintering temperature, more and more columnar Al2O3 grains grew instead of equiaxial grains, and the columnar grains length increased from 8μm to 22μm. The average ratio of length to diameter of columnar grains increased firstly and reached to the maximum of 5:1 at 1500°C, then keep unchanged. The fracture toughness increased with the increase of sintering temperature, from 4.83 to 6.48 MPa·m. Introduction Alumina (Al2O3) ceramic,as a kind of structural ceramics, is widely used in engineering due to its high hardness, high wear resistance and corrosion resistance, excellent high temperature stability, in addition to its low cost. At present the main problems of the application of alumina ceramics are still their high brittleness[1] and high sintering temperature[2]. The studies[3-6] of many types of ceramic materials confirmed that microwave sintering can reduce the sintering temperature and sintering time of alumina ceramic. Moreover, the additives doped to alumina matrix and then changing to liquid in the sintering process, can not only promote the densification of alumina but also make the columnar or sheet alumina grains obtained, which improves the toughness of alumina effectively. In this study, Al2O3 ceramics doped with 15%Nb2O5 and 7.5%La2O3 (volume percent) were prepared by microwave sintering. Furthermore, the effect of sintering temperature on the densification, microstructure and fracture toughness were investigated. Raw materials and experimental methods α-Al2O3 (99.6 wt%, average particle size of 4μm) powder are produced by LeiPu Ceramic Material Co. Ltd., Zibo, Shandong, China; Nb2O5 (99.99 wt%, average particle size of 8μm) and La2O3 (99.99 wt%, average particle size of 2μm) powder are both produced by Sinopharm Chemical Reagent Co. Ltd., Shanghai, China. The uniformly mixed powder was obtained after the ball milling of raw material powder followed by drying. Then the composite powder were prepressed into regular bars under a pressure of 100MPa with suitable amount of 5wt% solution of polyvinyl alcohol (PVA) as the binder, and then cold-isostatically pressed under 200MPa. After calcined in conventional furnace at 600°C for 3h to remove organic binder, the green samples were sintered in a 2.45GHz multimode microwave sintering furnace in air atmosphere. Altogether five kinds of samples with the same component of 15%Nb2O57.5%La2O377.5%Al2O3 were sintered at 1450°C, 1475°C, 1500°C, 1525°C, 1550°C respectively, for the same time of 30min. The densities of the sintered samples were measured by Archimedes method. The phase

(Pb0.945Bi0.027La0.01)(Nb0.95Ti0.0625)2O6 piezoelectric ceramic composition with high Curie temperature was synthesized via a conventional solid-state reaction method. The ceramics were sintered in the atmospheres of nitrogen (N2) and oxygen (O2). Effects of the sintering atmospheres on phase structure, microstructure, dielectric and piezoelectric properties of the ceramics were studied in detail. Ceramics sintered at the optimum sintering temperatures have the single orthorhombic ferroelectric phase. The atmosphere of O2 facilitates decreasing the sintering temperatures of the ceramics. The lattice parameters of the ceramics are related to the sintering atmospheres. Microstructures of the ceramics were studied via a scanning electron microscope. The values of dielectric constant remain almost unchanged at temperatures between room temperature and about 400 °C for all ceramics. Dielectric behavior was studied via the Curie–Weiss law and modified Curie–Weiss law. Compared with the ceramics sintered in N2, the Curie temperature of the ceramics sintered in O2 decreases slightly to 498 °C, while the piezoelectric charge constant of the ceramics sintered in O2 increases to 80 pC/N. For the ceramics sintered in O2, the d 33 value does not show an obvious decrease as the annealing temperature increases up to 450 °C, showing a high potential to be used in high-temperature applications as piezoelectric transducers.