复相陶瓷 BSTN的相组成和微观结构与 Sr/Ba比的关系

按配方(1-x)BaO·xSrO·0．7TiO2·0．3Nb2O5制备不同Sr／Ba比的钙钛矿／钨青铜复相陶瓷,用XRD和SEM研究其组成和结构与Sr／Ba比的关系．结果表明,改变Sr／Ba比对两相稳定共存没有影响;受同一体系中两相不同固溶能力控制,钙钛矿相中Ba2+和Sr2+之间的置换几率远大于钨青铜相中,其Sr／Ba比随体系Sr／Ba比变化,而钨青铜相的Sr／Ba比维持约0．667基本不变;控制体系Sr／Ba比偏离该值,钙钛矿相的晶格常数相应偏离标准值,而钨青铜相基本不变;提高Sr／Ba比,钙钛矿相晶粒尺寸减小,而钨青铜相变化不明显．两相共存体系中,当两相都可形成固溶体但固溶能力不同时,固溶度大的一相优先参与置换,并抑制另一相的固溶．     

钙钛矿/钨青铜两相复合BSTN陶瓷的形成与性能研究

设计了特殊配方0.7BaO.0.3SrO·(1-y)TiO₂·yNb₂O₅, 通过过量组成控制,制备了钙钛矿相和钨青铜相共存的复相陶瓷.用XRD和阻抗仪测试了相结构及介电常数.结果表明,在形成以钙钛矿为主相的体系中,Nb₂O₅过量6mol％以上时开始形成钨青铜相;在形成以钨青铜为主相的体系中,BaO和SrO过量11mol％以上时开始形成钙钛矿相.两相含量相当的体系中,钙钛矿相几乎不固溶Nb₂O₅,而钨青铜相固溶一定量TiO₂.复相陶瓷的介电性能具有BST和SBN两相的特点.BSTN复相体系中钨青铜相的铁电/顺电转变温度随固溶TiO₂量增加而降低,随钙钛矿相增加而升高,其最低转变温度约在200℃,比纯SBN相下降90℃.     

Structure, dielectric and magnetic properties of Ba6FeNb9O30 tungsten bronze ceramics

Ba₆FeNb₉O₃₀ ceramics were synthesized by a standard solid-state sintering process. X-ray powder diffraction (XRD) refinements were carried out to analyze the crystal structure, and the dielectric, ferroelectric and magnetic properties were investigated and discussed. The tetragonal tungsten bronze structure in space group P4bm was determined with the lattice parameters: a = 12.597(6) ?, b = 12.597(6) ?, c = 3.989(1) ?. An extremely high dielectric constant was indicated at higher temperatures, and it dropped quickly when the sample was cooled down through a critical temperature, and this critical temperature showed strong frequency dependence. This dielectric relaxation was more obviously observed in the dielectric loss curve. The nonlinear magnetic hysteresis curve was observed in the present ceramics at 5 K, which was related to the magnetic ions (Fe³⁺) in tungsten bronze structure.     

低温烧结Ph(Zn1/3Nb2/3)O3基复相陶瓷中的两相共存与介电性能

分别采用氟化物和硼硅玻璃为助烧剂制备了低温烧结ＰＺＮ基复相陶瓷，并借助介电温度特性研究了复相陶瓷中的两相共存与助烧剂的关系。结果表明，添加剂引入的晶格缺陷对复相陶瓷中的两相共存有显著影响。ＬｉＦ助烧剂因引起晶格氧空位促进两相固溶化，而ＭｇＦ２和硼硅玻璃助烧的ＰＺＮ复相陶瓷可保持两相共存。以硼硅玻璃为助烧剂获得了低温烧结、具有Ｘ７Ｒ温度稳定特性的ＰＺＮ基复相陶瓷。     

低温烧结Ph(Zn_(1/3)Nb_(2/3)O_3基复相陶瓷中的两相共存与介电性能

分别采用氟化物和硼硅玻璃为助烧剂制备了低温烧结PZN基复相陶瓷，并借助介电温度特性研究了复相陶瓷中的两相共存与助烧剂的关系．结果表明，添加剂引入的晶格缺陷对复相陶瓷中的两相共存有显著影响,LiF助烧剂因引起晶格氧空位促进两相固溶化，而MgF2和硼硅玻璃助烧的PZN复相陶瓷可保持两相共存．以硼硅玻璃为助烧剂获得了低温烧结、具有X7R温度稳定特性的PZN基复相陶瓷．     

Effect of Sintering Temperature on the Microstructure,Electrical, and Magnetic Properties of Bi 0 . 8 5 Eu 0 . 1 5 FeO 3 Ceramics

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 t o 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.     

Fabrication and dielectric properties of textured Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-BaTiO<Subscript>3</Subscript> ceramics by RTGG method

Grain-oriented Na_0.5Bi_0.5TiO₃-BaTiO₃ (NBTBT) ceramics were fabricated by reactive-templated grain growth using plate-like Bi_2.5Na_3.5Nb₅O₁₈ (BNN) as templates. The specimens are composed of NBTBT perovskite phase and BNN lay-structured phase. Textured ceramics have a brick-wall microstructure with strip-like grains aligning in the direction parallel to the casting plane and exhibit an {h00} preferred orientation. The texture fraction increases initially, and then decreases with increasing sintering temperature. The optimal sintering temperature is 1,185 °C where the texture fraction has a maximum value of 0.58 and d₃₃ is 98 pC/N. The textured NBTBT ceramics show evidence of relaxor ferroelectrics with diffuse phase transition and frequency dispersion because of composite biphasic structure.     

Crystal structure and dielectric properties of La3+ substituted Ba5LaTi3Ta7O30 ceramics

The effects of La³⁺ partial substitution for Ba²⁺ on crystal structure and dielectric properties were investigated for modification of Ba₅LaTi₃Ta₇O₃₀ ceramics. When the substitution x > 0.6, the sintering temperature obviously decreased. Superstructure peaks were observed for more La³⁺ substitution (x ≥ 2.4). The stability of the tetragonal tungsten bronze phase was discussed with electronegativity difference and tolerance factor. Lattice parameters decreased at first, and then slightly increased; while axial ratio decreased with increasing La content. Dielectric constant slightly increased when x < 1.2, then gradually declined with the increase of La substitutions for Ba. Dielectric loss was very low except x = 2.4. Temperature coefficient of dielectric constant (at 1 MHz) was remarkably improved. The variation of dielectric properties was discussed from the change of crystal structure as well as the effects of vacancies at A-sites and superstructure.     

Effect of La/Sn co-substitution for Ba/Ta on crystal structure and dielectric properties of Ba5NdTi3Ta7O30 ceramics

The effects of La/Sn co-substitution for Ba/Ta were investigated for the modification of Ba₅NdTi₃Ta₇O₃₀ ceramics. The modified ceramics (Ba_5–x La _x )NdTi₃(Ta_7–x Sn _x )O₃₀ exhibited single tetragonal tungsten bronze phase for x<1.5, while a small amount of secondary phase BaTi₄O₉ was observed for x>1.5. The lattice constants decreased with increasing La/Sn content, while the axial ratio 10^1/2c/a decreased when x was below 1.5, then slightly increased. With increasing La and Sn content, the temperature coefficient of dielectric constant (at 1 MHz) was remarkably lowered from –1560 ppm/ °C to –286 ppm/ °C, while the dielectric constant gradually reduced, and the dielectric loss slightly increased. There were some clear relationships between the temperature coefficient and bond valence, tolerance factor: the temperature coefficient of dielectric constant linearly increased when the bond valence of the ions at B sites increased, while the same effect occurred when the tolerance factor decreased. In addition, the stability of the tetragonal tungsten bronze phase is discussed in relation to electronic difference and tolerance factor.     

Microstructure and dielectric properties of CBS glass-doped Sr0.5Ba0.5Nb2O6 ceramic system

40CaO–20B₂O₃–40SiO₂ (abbreviate as CBS) glass-doped Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics were fabricated by solid-state ceramic route. The effects of CBS glass addition on the firing, the phase formation, the microstructure and dielectric characterization of SBN50 ceramics were investigated. Results show that the density of the samples firstly increase and then slightly decrease with increasing CBS glass content and the highest density achieved has been 97% of the theoretical density for the sample with 2% (mass fraction) CBS glass. The sintering temperature was significantly reduced from 1,350 to 1,100 °C. X-ray diffraction analysis shows the single phase tungsten bronze type structure is preserved up to 2% CBS glass. However, the samples with more than 5% CBS glass are found to have a secondary phase CaNbO₃. The diffuse character and the dielectric constant at room temperature increase as CBS glass content increases. The dielectric constant of the samples at the Curie temperature (T _c) firstly increases and then decreases with increasing the content of CSB glass. Interestingly, the grain sizes of SBN phase are found to obviously increase with increase in CBS glass doping level.     

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.     

A-site deficient perovskites Ba(M2+ 1/3Nb2/3)O3: microstructural attributes for a high quality factor

Slight A-site deficiency in ordered perovskites Ba(M²⁺ _1/3Nb_2/3)O₃(M - Co, Zn, Mg) is shown to promote the formation of single-phase dense ceramics, in which the microwave (MW) quality factor Q attains its maximum values. Any further decrease in the Ba concentration in Ba(M²⁺ _1/3Nb_2/3)O₃ always results in the formation of a multiphase material containing secondary phase with the tetragonal tungsten bronze (TTB) structure. The amount of TTB phase in the perovskite matrix was found to depend on both the Ba concentration and the sintering temperature. The composition and properties of the TTB phase are discussed in terms of their effect on the MW dielectric parameters of Ba(M²⁺ _1/3Nb_2/3)O₃ ceramics.     

铋含量对钛酸镧铋陶瓷结构和介电性能的影响

通过固相合成的方法制备了Bi3.25,LaxTi3O12（x=0．98～1．03，简称BLT）陶瓷。通过XRD，SEM和阻抗分析仪表征了陶瓷的晶体结构和晶体形貌，测试了陶瓷的介电频谱，结果表明陶瓷的晶体结构为典型的层状钙钛矿结构且不随Bi含量和温度的变化而改变；随着Bi含量的增加晶体形貌由棒状颗粒向片状颗粒转变，而且陶瓷的致密度也得到提高；介电常数随Bi含量的增加先增大后减小，并且在x=1．02时达到最大值。     

Effect of La/Sn co-substitution for Ba/Ta on crystal structure and dielectric properties of Ba5NdTi3Ta7O30 ceramics

The effects of La/Sn co-substitution for Ba/Ta were investigated for the modification of Ba₅NdTi₃Ta₇O₃₀ ceramics. The modified ceramics (Ba_5?x La _x )NdTi₃(Ta_7?x Sn _x )O₃₀ exhibited single tetragonal tungsten bronze phase for x<1.5, while a small amount of secondary phase BaTi₄O₉ was observed for x>1.5. The lattice constants decreased with increasing La/Sn content, while the axial ratio 10^1/2c/a decreased when x was below 1.5, then slightly increased. With increasing La and Sn content, the temperature coefficient of dielectric constant (at 1 MHz) was remarkably lowered from ?1560 ppm/ °C to ?286 ppm/ °C, while the dielectric constant gradually reduced, and the dielectric loss slightly increased. There were some clear relationships between the temperature coefficient and bond valence, tolerance factor: the temperature coefficient of dielectric constant linearly increased when the bond valence of the ions at B sites increased, while the same effect occurred when the tolerance factor decreased. In addition, the stability of the tetragonal tungsten bronze phase is discussed in relation to electronic difference and tolerance factor.     

Effect of sintering temperature on dielectric properties of Ba0.6Sr0.4TiO3–MgO composite ceramics prepared from fine constituent powders

Composite ceramics of Ba_0.6Sr_0.4TiO₃ + 60 wt.% MgO were prepared from fine constituent powders by sintering at 1200–1280 °C. The composite specimens sintered at the relatively low temperatures showed satisfactory densification due to fine morphology of the constituent powders. The elevation of sintering temperature promoted the incorporation of Mg²⁺ into the lattice of the Ba_0.6Sr_0.4TiO₃ phase and grain growth of the two constituent phases. The dependence of the dielectric properties on sintering temperature was explained in relation to the structural evolution. Controlling the sintering temperature of the composite was found to be important to achieve the desired nonlinear dielectric properties. Sintering at 1230 °C was determined to be preferred for the composite in terms of the nonlinear dielectric properties. The specimen sintered at the temperature attained a tunability of 17.3% and a figure of merit of 127 at 10 kHz and 20 kV/cm.     

Stabilization of the perovskite phase in Pb(Zn1/3, Nb2/3)O3 ceramics modified by Ba(Zn1/3, Nb2/3)O3 and BaTiO3

Stabilization of the perovskite phase in PZN-BT-BZN ceramics prepared by solid-state sintering was investigated. With the addition of BT and/or BZN, the amounts of perovskite phase in PZN ceramics increased, but the amount of pyrochlore phase decreased. Optimum calcination conditions for this system, to obtain PZN ceramics with the minimum amount of the pyrochlore phase, are a temperature range between 950 and 1000°C and a sintering time of 2–4 h. The perovskite phase of these systems could be 100% stabilized by the addition of more than 7 mol% BT, 8 and 10 mol% BTZN and BZN, respectively. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microstructure,dielectric and ferroelectric properties of barium zirconate titanate ceramics prepared by microwave sintering

Barium zirconate titanate ceramics were fabricated by microwave sintering. Effects of microwave sintering time on microstructure, dielectric and ferroelectric properties of barium zirconate titanate ceramics have been investigated. The result shows that the ceramic samples sintered at 2.5 kW for 15–30 min are single phase perovskite structure and there is no secondary phase observed. As the microwave sintering time extends, barium zirconate titanate ceramics become more uniform and the grain size increases. The data of dielectric properties indicate that the samples prepared by microwave sintering for 15–30 min are the ferroelectrics with diffuse phase transition and the diffuseness of phase transition weakens with the extending of microwave sintering time. As microwave sintering time increases, the remnant polarization increases initially and then decreases. Moreover, the remnant polarization and the coercive field of the samples sintered for 15 and 20 min decrease as measuring frequency increases, but the measuring frequency has little effect on ferroelectricity of the sample sintered for 30 min. The temperature dependences of hysteresis loops further prove that the samples are ferroelectrics with diffuse phase transition.     

Effect of vanadium doping on sintering and dielectric properties of strontium barium niobate ceramics

Strontium barium niobate, Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics doping up to 3 wt% V₂O₅ were fabricated by solid state reaction route, starting from raw materials (oxides and carbonates) of analytical grade. The phase composition, microstructure and dielectric properties were investigated by X-ray diffraction, scanning electric microscope and impedance analyzer. The results show that the addition of V₂O₅ improves sintering densification of SBN ceramic samples. The relative density of the samples firstly increases and then slightly decreases with increasing amounts of V₂O₅ and sintering temperature. With the help of the additive of 1 wt% V₂O₅, the relative density of the sample sintered at 1,280 °C for 3 h can reached 97.2%. Only single tetragonal tungsten bronze phase SBN exists in all the doped samples. With increase in V₂O₅ content, the dielectric constant of SBN ceramics at both room temperature and in the vicinity of the phase transition temperature increases significantly and the Curie temperatures (Tc) obviously shifts to low temperature as well as the dielectric loss remains below 0.06. The diffuseness in the phase transition is found to increase with increase in vanadium doping level. The addition of V₂O₅ results in an increased grain size associated with rod-like grain growth.     

Microstructure,dielectric properties and diffuse phase transition of barium stannate titanate ceramics

BaSn _x Ti_1–x O₃ (short for BTS) ceramics are prepared via the conventional solid state reaction method. The microstructures, diffuse phase transiton, dielectric and ferroelectric properties of BTS ceramics were investigated. These results indicate that Sn⁴⁺ ions have entered the unit cell maintaining the perovskite structure of solid solution. The incorporation of SnO₂ can limit grain growth in the BTS ceramics. The Curie temperature of BTS ceramics decreases with the increasing of tin content. Addition of tin can decrease dielectric loss of BTS ceramics at room temperature. The diffuseness of the phase transition of BTS ceramics enhances with the increasing of tin content. The coercive electric field (E _C) increases as tin content increases when x is 0.10–0.20. Moreover, the remanent polarization (P _r) of BTS ceramics decreases with the increasing of tin content.     

Aging effects on dielectric properties of barium neodymium titanium tantalate ceramics

The aging effects on crystal structures and dielectric properties were investigated in Ba_pNd_6−pTi_8−pTa_2+pO₃₀ (p = 3, 4 and 5) ceramics with tungsten bronze structure. From XRD analyses on fresh and aged specimens, the slight change of crystal constant was concluded in Ba_pNd_6−pTi_8−pTa_2+pO₃₀ ceramics. Strong aging effects on the dielectric properties were observed in the present ceramics. After aging, a slightly decreased dielectric constant was observed combined with a significantly reduced dielectric loss in all the three compositions. These results had been discussed in term of the disorder-order state of ions at A- and B-sites. From tolerance factor and electronegativity difference, the stability was discussed for the filled type tungsten bronze phase.