BaTiO 3 (BT) based dielectric ceramics have been extensively applied in electronic and electrical... more BaTiO 3 (BT) based dielectric ceramics have been extensively applied in electronic and electrical industries such as multilayer ceramic capacitors (MLCC), 1,2 random access memory, 3 and actuators 4 owing to their excellent dielectric properties. To meet the application requirements of working in harsh environments, 5 intense efforts have been devoted to maintain their high dielectric constant over a wide range of temperatures. 6,7 For example, forming solid solutions 8 and constructing core-shell structures 9 by doping with various additives are thought to be effective approaches to enhance the dielectric temperature stability of BT-based ceramics. The core-shell structure is a chemically heterogeneous structure within ceramics, which consists of three parts: pure BT grain core, paraelectric shell containing dopant elements and local gradients. It is generally thought that the combination of compositional gradient regions with various Curie temperatures results in a rather diffused and flat ε r-T curve. 10 Despite the fact that the core-shell structure formation mechanism remains uncertain, general consensus has been reached that a limited diffusion process of dopants into BT
Advanced materials (Deerfield Beach, Fla.), Jan 23, 2017
The demand for dielectric capacitors with higher energy-storage capability is increasing for powe... more The demand for dielectric capacitors with higher energy-storage capability is increasing for power electronic devices due to the rapid development of electronic industry. Existing dielectrics for high-energy-storage capacitors and potential new capacitor technologies are reviewed toward realizing these goals. Various dielectric materials with desirable permittivity and dielectric breakdown strength potentially meeting the device requirements are discussed. However, some significant limitations for current dielectrics can be ascribed to their low permittivity, low breakdown strength, and high hysteresis loss, which will decrease their energy density and efficiency. Thus, the implementation of dielectric materials for high-energy-density applications requires the comprehensive understanding of both the materials design and processing. The optimization of high-energy-storage dielectrics will have far-reaching impacts on the sustainable energy and will be an important research topic in ...
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2015
Ba 0.4 Sr 0.6)TiO 3 (BST) ceramics with various grain sizes (0.3-3.4 μm) were synthesized by the ... more Ba 0.4 Sr 0.6)TiO 3 (BST) ceramics with various grain sizes (0.3-3.4 μm) were synthesized by the oxalate coprecipitation method and prepared by plasma activated sintering and conventional solid-state sintering process. The effect of grain boundary on the energy storage properties and the dielectric relaxation characteristics of BST paraelectric ceramics (Curie point ≈ −67°C) with various grain sizes were investigated. The dielectric breakdown strength (simplified as BDS) is obviously improved and then deteriorated with decreasing grain size, accounting for the energy density variation. The enhancement of interfacial polarization at grain boundary layers has a negative effect on the BDS, leading to the decreased values for samples with grain size smaller than 0.7 μm. In addition, the insulation effect of grain boundary barriers was discussed based on the complex impedance spectroscopy analysis, which was found to play a dominant role in controlling the BDS with coarser grain size. Among them, the sharply decreased BDS for BST with grain size of 1.8 μm was believed to be attributed to the combination of lower grain boundary density and higher interfacial polarization, due to the significant increase of oxygen vacancies at higher sintering temperature.
The effects of TiO 2 additives on microstructure and microwave dielectric properties of α-CaSiO 3... more The effects of TiO 2 additives on microstructure and microwave dielectric properties of α-CaSiO 3-2 wt%Al 2 O 3 ceramics have been investigated in detail. Specifically, the TiO 2 addition results in the presence of two distinct phases, e.g. CaTiO 3 and CaTiSiO 5 , which can inhibit the growth of α-CaSiO 3 grains by surrounding their boundaries and also improve the bulk density of α-CaSiO 3-2 wt%Al 2 O 3 ceramics. However, the TiO 2 addition undermines the microwave dielectric properties of the title ceramics because the derived phases of CaTiO 3 and CaTiSiO 5 have poor quality factor. The τ f value is strongly correlated to the compositions and can be controlled through the compositional ratio. The α-CaSiO 3-2 wt% Al 2 O 3 ceramics containing 2.5 wt% of TiO 2 sintered at 1250 1C showed excellent microwave dielectric properties (ε r ¼ 7.88, Q Â f ¼24,412 GHz and τ f ¼ À0.52 ppm/1C).
ABSTRACT (1 − x)BNTBT-xNN ceramics were prepared by conventional solid state reaction method. X-r... more ABSTRACT (1 − x)BNTBT-xNN ceramics were prepared by conventional solid state reaction method. X-ray fluorescence analysis shows that the volatilization of Na element occurs during sintering process, the resulted concentration variation of defect dipoles facilitate the grain growth. XRD analysis and dielectric properties analysis indicate that rhombohedral polar phase and tetragonal weakly polar phase coexist in BNTBT ceramics at room temperature. By increasing the NN amount, the rhombohedral polar phase content sharply decreases, leading to a smaller remnant polarization. The dielectric anomaly corresponding to the depolarization temperature disappears from the temperature range investigated. According to the XRD results, the amount of tetragonal weakly polar phase decreases with increasing NN content and the structure evolves toward a pseudocubic symmetry. The phase structure change results in more slim P–E loops. The optimum energy storage properties was obtained for the composition of x = 0.10, with energy storage density of 0.71 J/cm3 at 7 kV/mm and a good temperature stability around 25–150 °C.
In the current work, the bulk ternary (0.85-x) BiFeO 3-xBaTiO 3-0.15PbTiO 3 (BF-BTx-PT, x=0.08-0.... more In the current work, the bulk ternary (0.85-x) BiFeO 3-xBaTiO 3-0.15PbTiO 3 (BF-BTx-PT, x=0.08-0.35) system has been studied as a potential high-temperature piezoceramics. Samples with various content of BT were prepared via solid-state route, and pure perovskite phase was confirmed by X-ray diffraction. The temperature dependence of dielectric constants confirmed the decrease of Curie temperature with increasing BT content. It was found that the morphotropic phase boundary (MPB) composition of BF-BTx-PT ceramics was in the vicinity of x=0.15, which exhibits optimal properties with piezoelectric constant d 33 of 60 pC/N, high Curie temperature of 550 ℃, and low sintering temperature of 920 ℃. Measurements also showed that the depoling temperature was 300 ℃, about 150 ℃ higher than that of commercialized PZT ceramics, which indicated good temperature stability. BF-BTx-PT ceramics are promising candidates for high temperature applications.
Journal of Materials Science: Materials in Electronics, 2014
Development of high-temperature piezoelectric sensors is of great interest for harsh environment ... more Development of high-temperature piezoelectric sensors is of great interest for harsh environment applications. The principal challenge for piezoelectric materials is their limitation for upper working temperature due to low Curie temperature and increasing conductivity at high temperatures. The effects of SiO 2 addition on the microstructure, ferro-piezoelectric and thermal stability of 0.8BiFeO 3-0.2BaTiO 3 lead-free piezoelectric ceramics were investigated. XRD results indicated all the samples crystallized into the rhombohedrally distorted perovskite structure which was independent of the SiO 2 addition. SiO 2 could obviously inhibit the grain growth possibly due to the accumulation of SiO 2 at the grain boundary. The leakage currents of 0.8Bi-FeO 3-0.2BaTiO 3 piezoceramics were remarkably reduced by certain amounts of added SiO 2 , facilitating the poling process, and improved their piezoelectric properties effectively. The optimal properties were obtained at the composition with 0.15 wt% SiO 2 addition which retained high transition temperature *628°C. The samples sintered in O 2 exhibited better thermal stability than those sintered in reduced atmospheres. Thus, SiO 2 proved to be a successful additive to improve the 0.8BiFeO 3-0.2BaTiO 3 piezoceramics for high-temperature applications, as a result of increased resistivity and enhanced piezoelectric activity.
The energy storage density of (1-x) BaTiO3 – x Ba(Mg1/3Nb2/3)O3 (x = 0, 0.1, 0.2, 0.3) ceramics w... more The energy storage density of (1-x) BaTiO3 – x Ba(Mg1/3Nb2/3)O3 (x = 0, 0.1, 0.2, 0.3) ceramics was investigated. The microstructure of samples was characterized by scanning electron microscopy (SEM). The energy storage density was calculated from the P-E hysteresis loops measured at room temperature. Experimental results show that the energy storage density of 0.9 BaTiO3 – 0.1 Ba(Mg1/3Nb2/3)O3 ceramics is highest among all compositions. At 15.8kV/mm electric field, the energy storage density of the sample can reach up to 1.07J/cm3, which is about 1.5 times higher than pure BaTiO3. The improvement of the energy density can be due to two factors: one is the improved breakdown strength caused by the optimized microstructure, the other is the decreased remnant polarization. This result indicates that bulk 0.9 BaTiO3 – 0.1 Ba(Mg1/3Nb2/3)O3 ceramic has advantages compared with pure BaTiO3 ceramic for energy storage applications, and with further improvements in microstructure and reducti...
Journal of Materials Science: Materials in Electronics, 2015
ABSTRACT The energy storage properties of Ca-doped (Sr, Ca)TiO3 (SCT) paraelectric ceramics have ... more ABSTRACT The energy storage properties of Ca-doped (Sr, Ca)TiO3 (SCT) paraelectric ceramics have been intensively investigated by traditional solid state sintering method. Phase structures and morphology were detected by the X-ray diffraction and SEM, respectively. The electric field strength dependence of polarization was measured and employed to calculate the energy storage density. The doped SCT ceramics exhibit high permittivity, low loss, and higher breakdown strength. At 333 kV/cm electric field strength, the energy storage density of the 2 mol % Ca-doped SrTiO3 ceramics with fine grain can achieve 1.95 J/cm3, which is 2.8 times of pure SrTiO3 in the literature, and its energy storage efficiency reaches 72.3 %. Therefore, the SCT ceramics might be a kind of promising energy storage dielectric material.
xBiAlO 3-(1 − x)BaTiO 3 [xBA-(1 − x)BT] polycrystalline ceramics were prepared by solid-state rea... more xBiAlO 3-(1 − x)BaTiO 3 [xBA-(1 − x)BT] polycrystalline ceramics were prepared by solid-state reaction method and sol-gel method, respectively. The ceramics were in tetragonal phase when x ≤ 0.1, transformed to pseudocubic at x > 0.1. The temperature stability of the dielectric constant for BA-BT was improved with BA contents increasing. Of particular interest was that the ceramics prepared by sol-gel method had less secondary phase, exhibiting much improved dielectric behavior. Among them, 0.3BA-0.7BT met the requirement of capacitance variation (C/C ≤ ±15%) in the temperature range of −55 to 440 • C with moderate dielectric constant (ε = 660) and low dielectric loss (tan δ = 1.2%) at room temperature (1 kHz). Nb-doped 0.2BA-0.8BT ceramics were investigated to improve the dielectric temperature stability at high-temperature end. It is found that all samples with 0.01-0.04 mol Nb addition satisfied the X8R specification.
BaTiO3-based ceramics with a core–double shell structure were fabricated by precipitation and the... more BaTiO3-based ceramics with a core–double shell structure were fabricated by precipitation and the sol–gel method.
Mixtures of 12 mol% CeO2-stabilised ZrO2 with 5 to 20 wt % Al2O3 were prepared and densified thro... more Mixtures of 12 mol% CeO2-stabilised ZrO2 with 5 to 20 wt % Al2O3 were prepared and densified through pressureless sintering in air at 1450° C for 1 to 4 h. The influence of the Al2O3 content and sintering time on the phase constitution, microstructure and mechanical properties of the as-sintered composites were investigated. Fully dense Ce-TZP/Al2O3 ceramics with a good combination of hardness and fracture toughness can be obtained by pressureless sintering in air for only 1 h. The addition of Al2O3 to Ce-TZP improves the mechanical properties and suppresses ZrO2 grain growth. The average ZrO2 grain size increases with increasing sintering time and decreasing Al2O3 content. This leads to an increase in toughness. An excellent fracture toughness of 14.3 MPam1/2 in combination with a Vickers hardness of 9.14 GPa was obtained for 12 mol % CeO2-TZP with 5 wt % Al2O3, sintered for 4 h.
2014 15th International Conference on Electronic Packaging Technology, 2014
(Ba<inf>0.4</inf>Sr<inf>0.6</inf>)TiO<inf>3</inf> (BST) parae... more (Ba<inf>0.4</inf>Sr<inf>0.6</inf>)TiO<inf>3</inf> (BST) paraelectric ceramics (T<inf>c</inf> ≈ −67 °C) with various grain sizes (0.6–1.8 μm) were synthesized by oxalate co-precipitation method and prepared by conventional solid-state sintering process. With decreasing grain sizes, the dielectric breakdown strength increases gradually. Based on the conductivity activation energy analysis, it was found that the larger grain boundary density plays a dominant role in controlling dielectric breakdown strength for samples with smaller grain sizes (1.0 to 0.6 μm). While with the growth of grain sizes above 1.0 μm, the sharply decreasing dielectric breakdown strength is induced by a combined effect of lower grain boundary density and more intensive interface polarization.
We investigated microstructures and energy storage properties of SiO 2-coated BaTiO 3 ceramics th... more We investigated microstructures and energy storage properties of SiO 2-coated BaTiO 3 ceramics that were prepared by the so-called Stöber process. The thickness of coating layer of BaTiO 3 powders could be effectively controlled by the silica content. It could be observed that the secondary phases Ba 2 TiSi 2 O 8 appeared in the coated BaTiO 3 ceramics due to the interdiffusion reactions between SiO 2 and BaTiO 3 components under sintering. BaTiO 3 cores in the coated ceramics remained up to the original grain size indicating the coating layer as an inhibitor. The results showed that both breakdown strength and energy density were improved apparently. The homogeneity of silica coating in the ceramics should dominate contribution to breakdown strength, which can reduce the weak-point breakdown under high electric field. The optimized composition for BaTiO 3 ceramic coated with 2.0 wt% SiO 2 showed the maximum energy storage density of 1.2 J/cm 3 with energy storage efficiency of 53.8%, which is about three times higher than that of pure BaTiO 3 (0.37 J/cm 3). 2015 Published by Elsevier Ltd.
ABSTRACT (K0.5Bi0.5)TiO3–BiScO3–PbTiO3 ceramics were synthesized by conventional solid-state meth... more ABSTRACT (K0.5Bi0.5)TiO3–BiScO3–PbTiO3 ceramics were synthesized by conventional solid-state method. A morphotropic phase boundary (MPB) was confirmed with the aid of structural analysis. Two dielectric anomalous peaks were observed, the one around dielectric maximum temperature (Tm) due to phase transformation from ferroelectric to paraelectric while the second one could be ascribed to space charges. Furthermore, the existence of space charges also resulted in the independence of Tm with frequency at low lead composition. A new high temperature piezoelectric ceramic, 0.30(K0.5Bi0.5)TiO3–0.30BiScO3–0.40PbTiO3 close to MPB exhibited excellent electrical properties with Tm of 384 °C, d33 of 247 pC/N, kp of 38.9%, Pr of 19.41 μC/cm2, and Ec of 2.25 kV/mm, indicative of a candidate for high temperature application.
The solid solutions in the 0.36BiScO 3-0.64(1 − x)PbTiO 3-0.64xPb(Sc 1/2 Nb 1/2)O 3 system were f... more The solid solutions in the 0.36BiScO 3-0.64(1 − x)PbTiO 3-0.64xPb(Sc 1/2 Nb 1/2)O 3 system were fabricated using wolframite precursor method. A coexistence of rhombohedral and tetragonal phases is formed in the studied compositions range and a wide morphotropic phase boundary region is confirmed by X-ray diffraction results. After the addition of Pb(Sc 1/2 Nb 1/2)O 3 , a relaxor behavior is induced and the dielectric maximum temperature shifts to higher temperatures with increasing measuring frequencies. The presence of relaxor can be ascribed to the formation of polar nanoregions. The studied composition exhibits the optimal ferroelectric and piezoelectric properties with d 33 of 453 pC/N and K p of 0.58, T m of 405°C for x = 0.10 composition, which is suitable for future high-temperature piezoelectric application.
Ba 0.4 Sr 0.6 )TiO 3 (BST) ceramics with various grain sizes (0.5-5.6 m) were prepared by convent... more Ba 0.4 Sr 0.6 )TiO 3 (BST) ceramics with various grain sizes (0.5-5.6 m) were prepared by conventional solid state reaction methods. The effect of grain size on the energy storage properties of BST ceramics (T c ≈ -65 • C) was investigated. With decreasing grain sizes, a clear tendency toward the diffuse phase transition was observed and the dielectric nonlinearity was reduced gradually, which can be explained by the Devonshire's phenomenological theory (from the viewpoint of intrinsic polarization). Based on the multi-polarization mechanism model, the relationship between the polarization behavior of polar nano-regions (the extrinsic nonlinear polarization mechanisms) and grain size was studied. The variation of the grain boundary density was thought to play an important role on the improvement of dielectric breakdown strength, account for the enhanced energy density, which was confirmed by the complex impedance spectroscopy analysis based on a double-layered dielectric model.
Phase evolution and ferroelectric behavior in 0.8BaTiO3-(0.2-x) BiScO3-xPbTiO3 ceramics, x = 0-0.... more Phase evolution and ferroelectric behavior in 0.8BaTiO3-(0.2-x) BiScO3-xPbTiO3 ceramics, x = 0-0.20, has been investigated in this paper. The phase assemblage and lattice parameters indicate the appearance of tetragonal-rhombohedral phase transition and the existence of a MPB region in the composition range x = 0.15-0.20. All these compositions exhibit relaxor ferroelectric behavior due to cation disorder for the substitution on the A-site by Bi and on the B-site by Sc. The dielectric permittivity of the specimens as well as the polarization decreases with increasing BiScO3. However, close to MPB region, the composition with dominance of rhombohedral phase (x = 0.15) exhibits higher remnant polarization than that with tetragonal for the more reorientational directions of the rhombohedral phase than that of the tetragonal one (x = 0.17).
ABSTRACT In this paper, the microstructures and the dielectric properties of xSrZrO3–(1−x)SrTiO3 ... more ABSTRACT In this paper, the microstructures and the dielectric properties of xSrZrO3–(1−x)SrTiO3 (x = 0.01, 0.03, 0.05, and 0.07) ceramics were investigated. The composition can form a single-phase structure solid solution as x increases from 0.01 to 0.07, and the average grain size decreases from 15 to 2 μm with the x increasing. With the variation of SrZrO3 content, dielectric constant, dielectric loss, and breakdown strength (BDS) of xSrZrO3–(1−x)SrTiO3 samples are changed. When x = 0.05, the samples exhibit high BDS more than 14 kV/mm and low dielectric loss about 1 × 10−3 with dielectric constant of 330. It can be a candidate material of energy storage for pulsed power application.
BaTiO 3 (BT) based dielectric ceramics have been extensively applied in electronic and electrical... more BaTiO 3 (BT) based dielectric ceramics have been extensively applied in electronic and electrical industries such as multilayer ceramic capacitors (MLCC), 1,2 random access memory, 3 and actuators 4 owing to their excellent dielectric properties. To meet the application requirements of working in harsh environments, 5 intense efforts have been devoted to maintain their high dielectric constant over a wide range of temperatures. 6,7 For example, forming solid solutions 8 and constructing core-shell structures 9 by doping with various additives are thought to be effective approaches to enhance the dielectric temperature stability of BT-based ceramics. The core-shell structure is a chemically heterogeneous structure within ceramics, which consists of three parts: pure BT grain core, paraelectric shell containing dopant elements and local gradients. It is generally thought that the combination of compositional gradient regions with various Curie temperatures results in a rather diffused and flat ε r-T curve. 10 Despite the fact that the core-shell structure formation mechanism remains uncertain, general consensus has been reached that a limited diffusion process of dopants into BT
Advanced materials (Deerfield Beach, Fla.), Jan 23, 2017
The demand for dielectric capacitors with higher energy-storage capability is increasing for powe... more The demand for dielectric capacitors with higher energy-storage capability is increasing for power electronic devices due to the rapid development of electronic industry. Existing dielectrics for high-energy-storage capacitors and potential new capacitor technologies are reviewed toward realizing these goals. Various dielectric materials with desirable permittivity and dielectric breakdown strength potentially meeting the device requirements are discussed. However, some significant limitations for current dielectrics can be ascribed to their low permittivity, low breakdown strength, and high hysteresis loss, which will decrease their energy density and efficiency. Thus, the implementation of dielectric materials for high-energy-density applications requires the comprehensive understanding of both the materials design and processing. The optimization of high-energy-storage dielectrics will have far-reaching impacts on the sustainable energy and will be an important research topic in ...
IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 2015
Ba 0.4 Sr 0.6)TiO 3 (BST) ceramics with various grain sizes (0.3-3.4 μm) were synthesized by the ... more Ba 0.4 Sr 0.6)TiO 3 (BST) ceramics with various grain sizes (0.3-3.4 μm) were synthesized by the oxalate coprecipitation method and prepared by plasma activated sintering and conventional solid-state sintering process. The effect of grain boundary on the energy storage properties and the dielectric relaxation characteristics of BST paraelectric ceramics (Curie point ≈ −67°C) with various grain sizes were investigated. The dielectric breakdown strength (simplified as BDS) is obviously improved and then deteriorated with decreasing grain size, accounting for the energy density variation. The enhancement of interfacial polarization at grain boundary layers has a negative effect on the BDS, leading to the decreased values for samples with grain size smaller than 0.7 μm. In addition, the insulation effect of grain boundary barriers was discussed based on the complex impedance spectroscopy analysis, which was found to play a dominant role in controlling the BDS with coarser grain size. Among them, the sharply decreased BDS for BST with grain size of 1.8 μm was believed to be attributed to the combination of lower grain boundary density and higher interfacial polarization, due to the significant increase of oxygen vacancies at higher sintering temperature.
The effects of TiO 2 additives on microstructure and microwave dielectric properties of α-CaSiO 3... more The effects of TiO 2 additives on microstructure and microwave dielectric properties of α-CaSiO 3-2 wt%Al 2 O 3 ceramics have been investigated in detail. Specifically, the TiO 2 addition results in the presence of two distinct phases, e.g. CaTiO 3 and CaTiSiO 5 , which can inhibit the growth of α-CaSiO 3 grains by surrounding their boundaries and also improve the bulk density of α-CaSiO 3-2 wt%Al 2 O 3 ceramics. However, the TiO 2 addition undermines the microwave dielectric properties of the title ceramics because the derived phases of CaTiO 3 and CaTiSiO 5 have poor quality factor. The τ f value is strongly correlated to the compositions and can be controlled through the compositional ratio. The α-CaSiO 3-2 wt% Al 2 O 3 ceramics containing 2.5 wt% of TiO 2 sintered at 1250 1C showed excellent microwave dielectric properties (ε r ¼ 7.88, Q Â f ¼24,412 GHz and τ f ¼ À0.52 ppm/1C).
ABSTRACT (1 − x)BNTBT-xNN ceramics were prepared by conventional solid state reaction method. X-r... more ABSTRACT (1 − x)BNTBT-xNN ceramics were prepared by conventional solid state reaction method. X-ray fluorescence analysis shows that the volatilization of Na element occurs during sintering process, the resulted concentration variation of defect dipoles facilitate the grain growth. XRD analysis and dielectric properties analysis indicate that rhombohedral polar phase and tetragonal weakly polar phase coexist in BNTBT ceramics at room temperature. By increasing the NN amount, the rhombohedral polar phase content sharply decreases, leading to a smaller remnant polarization. The dielectric anomaly corresponding to the depolarization temperature disappears from the temperature range investigated. According to the XRD results, the amount of tetragonal weakly polar phase decreases with increasing NN content and the structure evolves toward a pseudocubic symmetry. The phase structure change results in more slim P–E loops. The optimum energy storage properties was obtained for the composition of x = 0.10, with energy storage density of 0.71 J/cm3 at 7 kV/mm and a good temperature stability around 25–150 °C.
In the current work, the bulk ternary (0.85-x) BiFeO 3-xBaTiO 3-0.15PbTiO 3 (BF-BTx-PT, x=0.08-0.... more In the current work, the bulk ternary (0.85-x) BiFeO 3-xBaTiO 3-0.15PbTiO 3 (BF-BTx-PT, x=0.08-0.35) system has been studied as a potential high-temperature piezoceramics. Samples with various content of BT were prepared via solid-state route, and pure perovskite phase was confirmed by X-ray diffraction. The temperature dependence of dielectric constants confirmed the decrease of Curie temperature with increasing BT content. It was found that the morphotropic phase boundary (MPB) composition of BF-BTx-PT ceramics was in the vicinity of x=0.15, which exhibits optimal properties with piezoelectric constant d 33 of 60 pC/N, high Curie temperature of 550 ℃, and low sintering temperature of 920 ℃. Measurements also showed that the depoling temperature was 300 ℃, about 150 ℃ higher than that of commercialized PZT ceramics, which indicated good temperature stability. BF-BTx-PT ceramics are promising candidates for high temperature applications.
Journal of Materials Science: Materials in Electronics, 2014
Development of high-temperature piezoelectric sensors is of great interest for harsh environment ... more Development of high-temperature piezoelectric sensors is of great interest for harsh environment applications. The principal challenge for piezoelectric materials is their limitation for upper working temperature due to low Curie temperature and increasing conductivity at high temperatures. The effects of SiO 2 addition on the microstructure, ferro-piezoelectric and thermal stability of 0.8BiFeO 3-0.2BaTiO 3 lead-free piezoelectric ceramics were investigated. XRD results indicated all the samples crystallized into the rhombohedrally distorted perovskite structure which was independent of the SiO 2 addition. SiO 2 could obviously inhibit the grain growth possibly due to the accumulation of SiO 2 at the grain boundary. The leakage currents of 0.8Bi-FeO 3-0.2BaTiO 3 piezoceramics were remarkably reduced by certain amounts of added SiO 2 , facilitating the poling process, and improved their piezoelectric properties effectively. The optimal properties were obtained at the composition with 0.15 wt% SiO 2 addition which retained high transition temperature *628°C. The samples sintered in O 2 exhibited better thermal stability than those sintered in reduced atmospheres. Thus, SiO 2 proved to be a successful additive to improve the 0.8BiFeO 3-0.2BaTiO 3 piezoceramics for high-temperature applications, as a result of increased resistivity and enhanced piezoelectric activity.
The energy storage density of (1-x) BaTiO3 – x Ba(Mg1/3Nb2/3)O3 (x = 0, 0.1, 0.2, 0.3) ceramics w... more The energy storage density of (1-x) BaTiO3 – x Ba(Mg1/3Nb2/3)O3 (x = 0, 0.1, 0.2, 0.3) ceramics was investigated. The microstructure of samples was characterized by scanning electron microscopy (SEM). The energy storage density was calculated from the P-E hysteresis loops measured at room temperature. Experimental results show that the energy storage density of 0.9 BaTiO3 – 0.1 Ba(Mg1/3Nb2/3)O3 ceramics is highest among all compositions. At 15.8kV/mm electric field, the energy storage density of the sample can reach up to 1.07J/cm3, which is about 1.5 times higher than pure BaTiO3. The improvement of the energy density can be due to two factors: one is the improved breakdown strength caused by the optimized microstructure, the other is the decreased remnant polarization. This result indicates that bulk 0.9 BaTiO3 – 0.1 Ba(Mg1/3Nb2/3)O3 ceramic has advantages compared with pure BaTiO3 ceramic for energy storage applications, and with further improvements in microstructure and reducti...
Journal of Materials Science: Materials in Electronics, 2015
ABSTRACT The energy storage properties of Ca-doped (Sr, Ca)TiO3 (SCT) paraelectric ceramics have ... more ABSTRACT The energy storage properties of Ca-doped (Sr, Ca)TiO3 (SCT) paraelectric ceramics have been intensively investigated by traditional solid state sintering method. Phase structures and morphology were detected by the X-ray diffraction and SEM, respectively. The electric field strength dependence of polarization was measured and employed to calculate the energy storage density. The doped SCT ceramics exhibit high permittivity, low loss, and higher breakdown strength. At 333 kV/cm electric field strength, the energy storage density of the 2 mol % Ca-doped SrTiO3 ceramics with fine grain can achieve 1.95 J/cm3, which is 2.8 times of pure SrTiO3 in the literature, and its energy storage efficiency reaches 72.3 %. Therefore, the SCT ceramics might be a kind of promising energy storage dielectric material.
xBiAlO 3-(1 − x)BaTiO 3 [xBA-(1 − x)BT] polycrystalline ceramics were prepared by solid-state rea... more xBiAlO 3-(1 − x)BaTiO 3 [xBA-(1 − x)BT] polycrystalline ceramics were prepared by solid-state reaction method and sol-gel method, respectively. The ceramics were in tetragonal phase when x ≤ 0.1, transformed to pseudocubic at x > 0.1. The temperature stability of the dielectric constant for BA-BT was improved with BA contents increasing. Of particular interest was that the ceramics prepared by sol-gel method had less secondary phase, exhibiting much improved dielectric behavior. Among them, 0.3BA-0.7BT met the requirement of capacitance variation (C/C ≤ ±15%) in the temperature range of −55 to 440 • C with moderate dielectric constant (ε = 660) and low dielectric loss (tan δ = 1.2%) at room temperature (1 kHz). Nb-doped 0.2BA-0.8BT ceramics were investigated to improve the dielectric temperature stability at high-temperature end. It is found that all samples with 0.01-0.04 mol Nb addition satisfied the X8R specification.
BaTiO3-based ceramics with a core–double shell structure were fabricated by precipitation and the... more BaTiO3-based ceramics with a core–double shell structure were fabricated by precipitation and the sol–gel method.
Mixtures of 12 mol% CeO2-stabilised ZrO2 with 5 to 20 wt % Al2O3 were prepared and densified thro... more Mixtures of 12 mol% CeO2-stabilised ZrO2 with 5 to 20 wt % Al2O3 were prepared and densified through pressureless sintering in air at 1450° C for 1 to 4 h. The influence of the Al2O3 content and sintering time on the phase constitution, microstructure and mechanical properties of the as-sintered composites were investigated. Fully dense Ce-TZP/Al2O3 ceramics with a good combination of hardness and fracture toughness can be obtained by pressureless sintering in air for only 1 h. The addition of Al2O3 to Ce-TZP improves the mechanical properties and suppresses ZrO2 grain growth. The average ZrO2 grain size increases with increasing sintering time and decreasing Al2O3 content. This leads to an increase in toughness. An excellent fracture toughness of 14.3 MPam1/2 in combination with a Vickers hardness of 9.14 GPa was obtained for 12 mol % CeO2-TZP with 5 wt % Al2O3, sintered for 4 h.
2014 15th International Conference on Electronic Packaging Technology, 2014
(Ba<inf>0.4</inf>Sr<inf>0.6</inf>)TiO<inf>3</inf> (BST) parae... more (Ba<inf>0.4</inf>Sr<inf>0.6</inf>)TiO<inf>3</inf> (BST) paraelectric ceramics (T<inf>c</inf> ≈ −67 °C) with various grain sizes (0.6–1.8 μm) were synthesized by oxalate co-precipitation method and prepared by conventional solid-state sintering process. With decreasing grain sizes, the dielectric breakdown strength increases gradually. Based on the conductivity activation energy analysis, it was found that the larger grain boundary density plays a dominant role in controlling dielectric breakdown strength for samples with smaller grain sizes (1.0 to 0.6 μm). While with the growth of grain sizes above 1.0 μm, the sharply decreasing dielectric breakdown strength is induced by a combined effect of lower grain boundary density and more intensive interface polarization.
We investigated microstructures and energy storage properties of SiO 2-coated BaTiO 3 ceramics th... more We investigated microstructures and energy storage properties of SiO 2-coated BaTiO 3 ceramics that were prepared by the so-called Stöber process. The thickness of coating layer of BaTiO 3 powders could be effectively controlled by the silica content. It could be observed that the secondary phases Ba 2 TiSi 2 O 8 appeared in the coated BaTiO 3 ceramics due to the interdiffusion reactions between SiO 2 and BaTiO 3 components under sintering. BaTiO 3 cores in the coated ceramics remained up to the original grain size indicating the coating layer as an inhibitor. The results showed that both breakdown strength and energy density were improved apparently. The homogeneity of silica coating in the ceramics should dominate contribution to breakdown strength, which can reduce the weak-point breakdown under high electric field. The optimized composition for BaTiO 3 ceramic coated with 2.0 wt% SiO 2 showed the maximum energy storage density of 1.2 J/cm 3 with energy storage efficiency of 53.8%, which is about three times higher than that of pure BaTiO 3 (0.37 J/cm 3). 2015 Published by Elsevier Ltd.
ABSTRACT (K0.5Bi0.5)TiO3–BiScO3–PbTiO3 ceramics were synthesized by conventional solid-state meth... more ABSTRACT (K0.5Bi0.5)TiO3–BiScO3–PbTiO3 ceramics were synthesized by conventional solid-state method. A morphotropic phase boundary (MPB) was confirmed with the aid of structural analysis. Two dielectric anomalous peaks were observed, the one around dielectric maximum temperature (Tm) due to phase transformation from ferroelectric to paraelectric while the second one could be ascribed to space charges. Furthermore, the existence of space charges also resulted in the independence of Tm with frequency at low lead composition. A new high temperature piezoelectric ceramic, 0.30(K0.5Bi0.5)TiO3–0.30BiScO3–0.40PbTiO3 close to MPB exhibited excellent electrical properties with Tm of 384 °C, d33 of 247 pC/N, kp of 38.9%, Pr of 19.41 μC/cm2, and Ec of 2.25 kV/mm, indicative of a candidate for high temperature application.
The solid solutions in the 0.36BiScO 3-0.64(1 − x)PbTiO 3-0.64xPb(Sc 1/2 Nb 1/2)O 3 system were f... more The solid solutions in the 0.36BiScO 3-0.64(1 − x)PbTiO 3-0.64xPb(Sc 1/2 Nb 1/2)O 3 system were fabricated using wolframite precursor method. A coexistence of rhombohedral and tetragonal phases is formed in the studied compositions range and a wide morphotropic phase boundary region is confirmed by X-ray diffraction results. After the addition of Pb(Sc 1/2 Nb 1/2)O 3 , a relaxor behavior is induced and the dielectric maximum temperature shifts to higher temperatures with increasing measuring frequencies. The presence of relaxor can be ascribed to the formation of polar nanoregions. The studied composition exhibits the optimal ferroelectric and piezoelectric properties with d 33 of 453 pC/N and K p of 0.58, T m of 405°C for x = 0.10 composition, which is suitable for future high-temperature piezoelectric application.
Ba 0.4 Sr 0.6 )TiO 3 (BST) ceramics with various grain sizes (0.5-5.6 m) were prepared by convent... more Ba 0.4 Sr 0.6 )TiO 3 (BST) ceramics with various grain sizes (0.5-5.6 m) were prepared by conventional solid state reaction methods. The effect of grain size on the energy storage properties of BST ceramics (T c ≈ -65 • C) was investigated. With decreasing grain sizes, a clear tendency toward the diffuse phase transition was observed and the dielectric nonlinearity was reduced gradually, which can be explained by the Devonshire's phenomenological theory (from the viewpoint of intrinsic polarization). Based on the multi-polarization mechanism model, the relationship between the polarization behavior of polar nano-regions (the extrinsic nonlinear polarization mechanisms) and grain size was studied. The variation of the grain boundary density was thought to play an important role on the improvement of dielectric breakdown strength, account for the enhanced energy density, which was confirmed by the complex impedance spectroscopy analysis based on a double-layered dielectric model.
Phase evolution and ferroelectric behavior in 0.8BaTiO3-(0.2-x) BiScO3-xPbTiO3 ceramics, x = 0-0.... more Phase evolution and ferroelectric behavior in 0.8BaTiO3-(0.2-x) BiScO3-xPbTiO3 ceramics, x = 0-0.20, has been investigated in this paper. The phase assemblage and lattice parameters indicate the appearance of tetragonal-rhombohedral phase transition and the existence of a MPB region in the composition range x = 0.15-0.20. All these compositions exhibit relaxor ferroelectric behavior due to cation disorder for the substitution on the A-site by Bi and on the B-site by Sc. The dielectric permittivity of the specimens as well as the polarization decreases with increasing BiScO3. However, close to MPB region, the composition with dominance of rhombohedral phase (x = 0.15) exhibits higher remnant polarization than that with tetragonal for the more reorientational directions of the rhombohedral phase than that of the tetragonal one (x = 0.17).
ABSTRACT In this paper, the microstructures and the dielectric properties of xSrZrO3–(1−x)SrTiO3 ... more ABSTRACT In this paper, the microstructures and the dielectric properties of xSrZrO3–(1−x)SrTiO3 (x = 0.01, 0.03, 0.05, and 0.07) ceramics were investigated. The composition can form a single-phase structure solid solution as x increases from 0.01 to 0.07, and the average grain size decreases from 15 to 2 μm with the x increasing. With the variation of SrZrO3 content, dielectric constant, dielectric loss, and breakdown strength (BDS) of xSrZrO3–(1−x)SrTiO3 samples are changed. When x = 0.05, the samples exhibit high BDS more than 14 kV/mm and low dielectric loss about 1 × 10−3 with dielectric constant of 330. It can be a candidate material of energy storage for pulsed power application.
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