微波烧结对PLZT陶瓷电学性能的影响

采用部分共沉淀法制备锆钛酸铅镧(PLZT)粉体, 分别用普通马弗炉和微波马弗炉进行烧结成瓷, 对比分析不同烧结方法对PLZT陶瓷的晶体结构、微观形貌和电学性能的影响。结果表明: 微波烧结和常规烧结均成功制备出钙钛矿相PLZT陶瓷。采用微波烧结得到的PLZT陶瓷样品比常规烧结的晶粒细小, 尺寸更均匀, 孔洞较少; 在电学性能相近时, 微波烧结温度远低于常规烧结, 且保温时间远小于常规烧结。在1000℃进行微波烧结, 陶瓷的介电常数ε_r和压电常数d₃₃最大, ε_r为2512, d33为405 pC/N, 此时, 剩余极化强度为16.5 kV/cm, 矫顽场为8.2μC/cm²; 在1250℃常规烧结, 陶瓷的介电常数最大, 为2822, 压电常数最大, 为508 pC/N, 剩余极化强度为21.6 kV/cm, 矫顽场为9.6μC/cm²。     

Ferroelectric and piezoelectric properties of (1 − x) (Bi0.5Na0.5)TiO3–xBaTiO3 ceramics

Lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT)–barium titanate (BaTiO₃,BT) have been prepared by solid state reaction process. The (1?x)BNT–(x)BT (x = 0.01,0.03,0.05,0.07) ceramics were sintered at 1,150 °C for 4 h in air, show a pure perovskite structure. X-ray diffraction analysis indicates that a solid solution is formed in (1?x)BNT–(x)BT ceramics with presence of a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at x = 0.07. Raman spectroscopy shows the splitting of (TO₃) mode at x = 0.07 confirming the presence of MPB region. The temperature dependence dielectric study shows a diffuse phase transition with gradual decrease in phase transition temperature (T_m). The dielectric constant and diffusivity increases with increase in BT content and is maximum at the MPB region. With the increase in BT content the maximum breakdown field increases, accordingly the coercive field (E_c) and remnant polarization (P_r) increases. The piezoelectric constant of (1 ? x)BNT–(x)BT ceramics increases with increase in BT content and maximum at x = 0.07, which is the MPB region. The BNT–BT system is expected to be a new and promising candidate for lead-free dielectric and piezoelectric material.     

Effect of sintering temperature on the grain growth and electrical properties of barium zirconate titanate ferroelectric ceramics

In the present work, structural, dielectric and ferroelectric properties of barium zirconate titanate ferroelectric ceramics have been investigated. The specimens were synthesized using a solid state reaction technique. The XRD analysis reveals that the synthesized compound was formed with no secondary phases. As the sintering temperature increases from 1,200 to 1,300 °C, the average grain size is observed to increase from ~0.39 to ~6.15 μm. The dielectric measurements as a function of temperature show a decrease in Curie temperature (T_C) on increasing the sintering temperature. The decrease in Curie temperature is attributed to the substitution of Zr⁺⁴ whose ionic radius is larger than Ti⁺⁴. A large increase in the dielectric constant with the increase in grain size is observed. The remanent polarization is also observed to increase with the increase in grain size.     

烧结温度对锆钛酸铅-铌镁酸铅压电陶瓷结构的影响

采用铌铁矿预产物合成法在不同烧结温度下制备组成在准同型相界附近的锆钛酸铅-铌镁酸铅压电陶瓷。采用X射线衍射、拉曼光谱、扫描电镜以及介电温谱对制备陶瓷样品进行表征分析和性能测试。结果表明:所有陶瓷样品的相组成均为纯钙钛矿相;随着烧结温度的升高,陶瓷的相结构由菱方-四方两相共存转变为单一菱方相。对陶瓷断口的观察表明:随着烧结温度的升高,晶粒逐渐长大,陶瓷逐渐致密;陶瓷的平均晶粒尺寸约为3~4μm。制备的压电陶瓷在1 200℃烧结的试样峰值相对介电常数高达19 520,居里温度为310℃。     

Structural refinement,optical and electrical properties of [Ba1−x Sm2x/3](Zr0.05Ti0.95)O3 ceramics

Samarium doped barium zirconate titanate ceramics with general formula [Ba_1?x Sm_2x/3](Zr_0.05Ti_0.95)O₃ [x = 0, 0.01, 0.02, and 0.03] were prepared by high energy ball milling method. X-ray diffraction patterns and micro-Raman spectroscopy confirmed that these ceramics have a single phase with a tetragonal structure. Rietveld refinement data were employed to model [BaO₁₂], [SmO₁₂], [ZrO₆], and [TiO₆] clusters in the lattice. Scanning electron microscopy shows a reduction in average grain size with the increase of Sm³⁺ ions into lattice. Temperature-dependent dielectric studies indicate a ferroelectric phase transition and the transition temperature decreases with an increase in Sm³⁺ ion content. The nature of the transition was investigated by the Curie–Weiss law and it is observed that the diffusivity increases with Sm³⁺ ion content. The ferroelectric hysteresis loop illustrates that the remnant polarization and coercive field increase with an increase in Sm³⁺ ions content. Optical properties of the ceramics were studied using ultraviolet–visible diffuse reflectance spectroscopy.     

Effect of sintering atmosphere on the microstructure and dielectric properties of barium strontium titanate glass–ceramics

The sintering of barium strontium titanate glass–ceramics in nitrogen modified their dielectric properties significantly compared to the sintering in air. The experimental results demonstrate that the glass–ceramics sintered at low temperatures contain a major phase Ba₂TiSi₂O₈ (BTS), known as fresnoite. The fresnoite phase disappeared and the barium strontium titanate perovskite phase became the major phase when the sintering temperature was increased. In addition, the microstructure observation showed that both the proportion of crystal phase and the crystal size increase obviously with the increase of sintering temperature. Most importantly, impedance spectroscopy has been employed to study the electrical responses arising from the glass and the crystal phases in the glass–ceramics sintered at low temperatures and high temperatures. The magnitudes of impedance and modulus changed significantly for the glass–ceramics sintered at the two temperature ranges. The activation energy calculated from the complex impedance, complex modulus and dc conductivity suggests that the dielectric relaxation for the glass phase and the glass–crystal interface may be attributed to the motion of the dipole associated with oxygen vacancy. And for the barium strontium titanate perovskite glass–ceramics, the motion of the electrons from the second ionization of oxygen vacancies leads to dc electrical conduction. The mechanism for the giant dielectric properties of the glass–ceramics sintered at high temperatures in nitrogen is discussed.     

Influence of microstructure on dielectric properties of Nd-doped barium titanate synthesized by hydrothermal method

Nd-doped barium titanates were successfully synthesized via a hydrothermal route. The as-prepared barium titanate was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transformation infrared spectroscopy (FTIR), and Vis–NIR spectroscopy respectively. The results show that pure and Nd-doped barium titanate powders have cubic perovskite structure. After sintering at a temperature of 1,250 °C for 2 h, the phase compositions of all barium titanate are tetragonal phase structure. Vis–NIR spectra well confirmed that Nd³⁺ have been doped into barium titanate. The particle diameters of Nd-doped barium titanate powders and ceramics become samller with the increase of Nd³⁺ content. When Nd/Ba molar ratio is 0.02, the dielectric loss (0.0008) of the powder measured at 1 MHz and room temperature dramatically decreases by 99 % comparing with pure barium titanate (0.083) and shows frequency independence with the frequency increasing from 40 Hz to 1 MHz. The dielectric constant and dielectric loss are 436 and 0.09 after sintering. The Nd-doped BaTiO₃ show an improvement in the dielectric quality which possess a decreased sensitivity to frequency for both the dielectric constant and dielectric loss. Such improvements are of potential importance for high energy density and low loss.     

Effect of calcining temperature on microstructures and electrical properties in modified lead zirconate titanate ceramics

The effect of calcining temperature on microstructures and electrical properties of modified lead zirconate titanate ceramics has been investigated. Specimens of the modified lead zirconate titanate ceramics, formed with different powders calcined over the temperature range from 800 to 950 °C, were prepared by roll forming process. It is observed that the calcining temperature of the powders alters the grain size, which, in turn, modifies the electrical properties of the ceramics. The results also show that dielectric constant, saturated polarization and piezoelectric coefficient tend to increase with increasing calcining temperature up to 900 °C and then to sharply decrease. The best electrical properties were obtained from the samples with the calcining temperature of 900 °C. At the lower calcining temperatures, a small PbO excess seems to result in PbO-rich grain boundaries and anomalous grain growth during sintering process. In addition, when the calcining temperature was increased to 950 °C, a PbO deficiency appears to take place by breaking up the stoichiometry.     

Effect of sintering condition on microstructure and dielectric properties of BSTN composite ceramics

The effect of sintering condition on the phase composition, microstructure and dielectric properties of barium strontium titanate niobate (BSTN) composite ceramics, in which the perovskite phase and the tungsten bronze phase coexisted, was investigated by XRD, SEM and LCZ Meter. The results show that more Sr²⁺ ions dissolved from the grain boundaries into the crystal lattice of the pervoskite phase and the tungsten bronze phase, especially, into the lattice of the pervoskite phase with the increasing of sintering temperature and sintering time, respectively. So the Curie temperature point decreases with the increasing of sintering temperature. The crystal growth rate of the tungsten bronze phase is higher than that of the perovskite phase in BSTN composite ceramics as the sintering temperature increases. The reasonable sintering temperature is about 1275 °C for BSTN composite ceramics. The activation energy to setting up polarization in BSTN composite ceramics increases with the increase of the applied frequency.     

Effects of lanthanum modification on electrical and dielectric properties of Pb(Zr0.70,Ti0.30)O3 ceramics

Lanthanum modified lead zirconate titanate ceramics with lanthanum content changing from 7.6 to 9.0 at.% La and a Zr/Ti ratio of 70/30 (PLZT 100x/70/30) have been prepared by conventional high temperature solid-state reaction technique. The studies of the ferroelectric, electromechanical and dielectric properties of the ceramics were carried out. The results showed the enhanced antiferroelectricity stability when the lanthanum content increases. The polarization and strain decreased with the increasing La content. The dielectric spectra of all the PLZT samples show a dispersive behavior. With increasing La concentration, the maximum dielectric constants ε_m and the transition temperatures T_m were reduced.     

Effect of sintered temperature on structural and piezoelectric properties of barium titanate ceramic prepared by nano-scale precursors

Lead-free piezoelectric ceramics barium titanate has been successfully fabricated by a facile modified (nano-scale precursors) solid phase method. The sintered temperature was employed as the main regulatory factor to control the growth of the grain size and crystallinity of the sample. When the sintered temperature was set as 1350?°C, the pure phase barium titanate ceramics could be prepared with the grain size of about 1 μm. In addition, piezoelectric tests showed that, the samples sintered at this temperature possessed the maximum ?_r, P_r and d₃₃ values, 3533, 16.24 μC/cm² and 420 pC/N, respectively. These characteristics make them promising candidates as lead-free piezoelectric ceramic materials.     

Phase transition characteristics and dielectric properties of rare-earth (La,Pr, Nd,Gd) doped Ba(Zr0.09Ti0.91)O3 ceramics

A-site deficient rare-earth doped barium zirconate titanate (BZT) ceramics (Ba_1−yLn_2y/3)Zr_0.09Ti_0.91O₃ (Ln = La, Pr, Nd, Gd) are obtained by a modified solid-state reaction method. Perovskite-like single-phase compounds were confirmed from X-ray diffraction data. Morphological analysis on sintered samples shows that the addition of rare-earth ions inhibits the growth of the grain and remarkably changes the grain morphology. The effect of rare-earth addition to BZT on phase transition and dielectric properties is analyzed. A dramatic fall in the transition temperature occurs when BZT ceramic is doped with rare-earths. Moreover, diffusivity degree of the phase transition increases and a relaxor-type behaviour is induced due to both the increment of the lanthanide content and the increase of the ionic radius of the dopant element. High values of dielectric tunability are obtained for lanthanum doped BZT. A direct relation between transition temperature and tunability is discussed. Conclusively, low permittivity and high tunability materials can be obtained by the adequate substitution of rare-earths into BZT ceramics.     

Preparation and microwave dielectric properties of Bi2Ti4O11 ceramics

Single phase of Bi₂Ti₄O₁₁ ceramics, which belong to meta-stable phase compounds, were synthesized by controlling the reaction time through conventional solid-state method. The effects of annealing time on phase composition of Bi₂Ti₄O₁₁ ceramic powders and sintered ceramics were studied by XRD analysis. Second phase Bi₂Ti₂O₇ appeared when the annealing time shorter than 4 h. However, pure phase of Bi₂Ti₄O₁₁ powders can be formed by prolonging the annealing time to 6 h at 1,000 °C. The sintering temperatures on microstructure and microwave dielectric properties of Bi₂Ti₄O₁₁ ceramics were investigated. The results show that ceramics sintered at 1,075–1,175 °C are single phase of Bi₂Ti₄O₁₁ and present two different sizes of prismatic shape grains. Smaller size crystals grow into larger ones with increasing sintering temperature. The ceramics sintered at 1,125 °C reach a maximum density and have a microwave dielectric properties of ε_r = 51.2, Q × f = 3,050 GHz and τ_f = ?297 ppm/°C.     

Dielectric and magnetic properties of DyMnO3 ceramics

This paper reports the dielectric and magnetic properties of DyMnO₃ (DMO) ceramics sintered at 1,100 and 1,350 °C temperature for 10 h. Sample sintered at 1,100 °C showed presence of secondary phases of Dy₂O₃ whereas the monophasic orthorhombic structure of DyMnO₃ sample is synthesized only at sintering temperature of 1,350 °C. The dielectric properties of the sintered sample of DMO were investigated as a function of temperature (T ≥ 300 K) and frequency (10 kHz–1 MHz). Both the sintered samples showed frequency independent dielectric anomaly at 313 K. These samples exhibited ferroelectric behavior at room temperature which was evidenced from the polarization hysteresis loop measurement. No magnetic transition has been observed at room temperature. However, magnetic field dependent magnetization and temperature dependent magnetization showed the paramagnetic behavior of the DyMnO₃ samples.     

还原气氛烧成Y5V型瓷粉的结构与介电性能

运用SEM、TEM、XRD等手段研究了掺杂组分对钛酸钡基Y5V陶瓷的结构和性能影响.结果表明:由于掺杂组分的存在,烧结情况得到了明显的改进.掺杂钛酸钡陶瓷的烧结包括固-固烧结和液-固烧结.Zr和稀土元素能够扩散进入钛酸钡晶格并促进固-固烧结,SiO2主要聚集在晶界并促进液-固烧结烧结.Nd5 聚集在晶界并促进针状颗粒生成,XRD的结果表明样品中有新相形成.由于掺杂的引入,材料的居里温度向低温方向移动,材料的介温曲线较纯钛酸钡材料的介温曲线更趋平坦.研究的结果还表明,由于在还原气氛中烧结,材料的介电损耗上升.     

Effect of crystallizable glass addition on sintering and dielectric behaviors of barium titanate ceramics

A crystallizable glass which can precipitate barium titanate was added to BaTiO₃ ceramics to study its effect on sintering behavior and dielectric properties of the composites. High densification (>95 % theoretical density) was achieved by addition of glass phase and the dielectric constant of composites was enhanced through the crystallization of glass phase. A composite with 90 wt% BaTiO₃ and 10 wt% glass showed a dielectric constant of ~2,300 at room temperature at 1 kHz and a dielectric breakdown strength about 140 kV/cm.     

Fabrication of hydrothermal ageing resistant of 3 mol % yttria-stabilised tetragonal zirconia polycrystalline via microwave sintering

The influence of microwave sintering on the densification, mechanical performances, microstructure evolution and hydrothermal ageing behaviour of pure 3 mol % yttria-stabilised tetragonal zirconia polycrystalline (3Y-TZP) ceramics was compared with conventional sintered samples. Green bodies were sintered via conventional pressure-less and microwave sintering method between 1200 °C to 1400 °C with dwelling time and firing rate at 120 min, 10 °C/min and 1 min, 20 °C/min. Result showed that reduced processing temperature and holding time is possible with microwave sintering technique for fabricating good resistant zirconia sample with bulk density, Young's modulus, and Vicker's hardness that are comparable to samples sintered with conventional method. However, the microwave sintered samples suffered from hydrothermal ageing where their average grain size is above critical size. The enhancement of hydrothermal ageing resistance of the sintered samples is associated with the decreasing grain size of the sintered samples instead of sintering method.     

Reaction sintering of nano-sized ZnO–Nb2O5 powder mixture: sintering,microstructure and microwave dielectric properties

Sintering behavior, microstructures and microwave dielectric properties of ZnNb₂O₆ (ZN) ceramics prepared by reaction-sintering method were investigated. The X-ray diffraction patterns of the sintered samples revealed single-phase formation with a columbite structure after 1–5 h sintering at 1,025–1,125 °C. After sintering at 1,125 °C for 5 h, the ZN ceramics with the density of 5.56 g/cm³ (98.9 % of the theoretical density) and good microwave dielectric properties of ε_r = 23.9, Q × f = 51,000 and τ_f = ?62 ppm/°C were obtained. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the ZN ceramics for applications on microwave dielectric resonators.     

Effect of sintering temperature on the microstructure and electrical properties of zirconium doped barium titanate ceramics

Lead-free Ba(Zr_0.15Ti_0.85)O₃ (BZT15) ceramics were synthesized by adopting the solid-state synthesis method. The effect of increasing sintering temperature (T_s) in the range of 1,350–1,450 °C on the microstructure, dielectric, polarization, and electric field induced strain of the ceramics was studied. Fine grained (~260 nm) BZT15 ceramics displayed single phase perovskite structure with relative densities >94 % of the theoretical density. Both grain size and shape were influenced by the sintering parameters. With increase in T_s, not only the maximum dielectric constant decreased from 11,412 to 8,734 along with an increase in the degree of diffuseness, but also interestingly the Curie temperatures were found to vary within an interval of 61–73 °C. Optimum sintering temperature has been found resulting in high remnant polarisation and strain in these ceramics. The properties observed are attributed to a contribution from all polar vectors present in coexistent phases.     

A new route to improve microwave dielectric properties of low-temperature sintered Li2TiO3-based ceramics

Low-temperature sintered Li₂TiO₃-based ceramics for low temperature co-fired ceramic resonators were synthesized by a solid state reaction method. Their microwave dielectric properties were further improved by CeO₂ addition. When the amount of CeO₂ increased, the relative permittivity (ε _r ) of the samples increased a little and then decreased. The quality factor (Q × f) of the samples was improved obviously for a higher standard reduction potential of cerium than that of titanium. The temperature coefficient of resonant frequency (τ _f ) of the samples decreased with the increase of CeO₂ addition. CeO₂ mainly existed as a secondary phase and it facilitated the sintering of the Li₂TiO₃-based ceramics. Typical microwave dielectric properties of ε _r  = 22.97, Q × f = 34,881 GHz, and τ _f  = 33.12 ppm/°C were obtained for Li₂TiO₃ + 2 wt% ZnO–B₂O₃ frit + 0.9 wt% CeO₂ ceramics sintered at 920 °C for 4 h. The addition of oxidizers was proved a promising route to improve the microwave dielectric properties of titanate ceramics sintered at low temperatures.