Grain-oriented fabrication of bismuth titanate ceramics and its electrical properties

The concept of grain-oriented fabrication in ceramics, which utilizes anisotropy either in morphology or some specific property of the particle, is reviewed. A fabrication method, which maximizes the grain orientation, is described for Bi(4)Ti(3)O(12 ). The process utilized plate-like morphology of Bi(4)Ti (3)O(12) particles and yielded a ceramic with an X-ray density of 95.4% and an unprecedented value of 100% for Lotgering's orientation factor in the direction of orientation. The dielectric and piezoelectric properties of this ceramic are described and compared to single crystal values. Complex impedance analysis of the ceramics was used to explain the dielectric relaxations at elevated temperatures. The use of grain-oriented fabrication as a practical technique for making polycrystalline ceramics with electrical properties close to those of single crystals (in the direction of orientation) is emphasized. The use of grain-oriented Bi(4)Ti(3)O(12) ceramics as a high-temperature piezoelectric transducer is suggested.     

Field-induced strain behavior for potassium sodium bismuth titanate ceramics

Data are reported for the dielectric, piezoelectric, electrostrictive, and ferroelectric properties of potassium-substituted sodium bismuth titanate, [(K(x)Na(1-x))(0.5)Bi(0.5)]TiO3. For the morphotropic phase boundary composition x = 0.2, relaxor-type behavior was observed at room temperature with piezoelectric (effective d(333) = 325 x 10(-12) m/V) and ferroelectric properties (P(R) = 25 microC/cm(2), E(C) = 30 kV/cm). A transition to a relatively frequency-independent, diffuse phase transformation region occurred with increasing temperature, with no remanent strain or coercive field. Above the transition temperature, the field-induced strain was consistent with contributions from electrostriction and field induced piezoelectricity (M(3333) = 1.9 x 10(-16) m2/V2 and d333 = 81 x 10(-12) m/V at 100 degrees C). Information is given for the temperature dependence of properties, e.g., 0.14% strain induced at 50 kV/cm at 200 degrees C. Higher potassium content x = 0.6 stabilized the ferroelectric piezoelectric region to temperatures above 200 degrees C, with a relatively stable d(333) = 150-145 x 10-12 m/V between 25 degrees C and 200 degrees C. Pb-free KNBT ceramics appear competitive with PZT, especially for higher temperature electromechanical applications.     

钛酸铋钠基无铅压电陶瓷研究近期进展

钛酸铋钠(分子式是Bi0.5Na0.5TiO3,简写为BNT)基无铅压电陶瓷性能优良,但与铅基陶瓷相比还有相当的差距,其性能有待进一步提高.从BNT基陶瓷改性、陶瓷新体系以及陶瓷制备技术等多方面,分析了提高BNT基陶瓷性能的原理、途径和方法,指出了发明陶瓷新体系的有关思路,讨论了陶瓷制备技术与陶瓷性能的关系.同时,列举了近期在BNT基陶瓷性能改善研究中的若干新进展和新结果、性能良好的BNT基陶瓷新体系及制备工艺和制备新技术对陶瓷性能的影响,并对今后的相关研究进行了展望.     

Role of strain and lattice distortion on ferroelectric and piezoelectric properties of bismuth magnesium zirconate substituted sodium bismuth titanate ceramics

Effect of weak ferroelectric perovskite, bismuth magnesium zirconate [Bi(Mg_0.5Zr_0.5)O₃] substitution in lead-free sodium bismuth titanate [(Na_0.5Bi_0.5)TiO₃] ceramics is studied. Influence of substitution on intrinsic and extrinsic contribution and impact on ferroelectric and piezoelectric properties are investigated. Improved spontaneous polarization (P_s), increased remnant polarization (P_r), decreased coercive field (E_c) and high piezoelectric coefficient (d₃₃) are obtained for x = 0.01 mole fraction of Bi(Mg_0.5Zr_0.5)O₃ substitution due to decrease in rhombohedral lattice distortion and homogeneous strain. Small rhombohedral lattice distortion (δ_r) and minimum homogeneous strain (δ) are the primary intrinsic parameters which favours the extrinsic parameters such as mobility of non-180° domain reorientation, domain switching and domain wall motion. Enhanced mobility softens the coercive field and increases remnant polarization to maximum. Reduced rhombohedral lattice distortion, low strain and enhanced mobility are the key factors for enhanced piezoelectric constant, highest remnant polarization and decreased coercive field in non-MPB (1 ? x)(Na_0.5Bi_0.5)TiO₃–xBi(Mg_0.5Zr_0.5)O₃ solid solutions.     

Pyroelectricity in calcium substituted sodium bismuth titanate layer structured ferroelectric ceramics

Pyroelectric properties of bismuth layer structured calcium substituted sodium bismuth titanate (Na_0·5Bi_0·5)_1−x Ca _x Bi₄Ti₄O₁₅ withx=0 (NBT) andx=0·1 (0·1 NCBT) were studied by measuring the current under short circuit condition. Spontaneous polarization and figures of merit were evaluated from the measured values of pyroelectric coefficients, dielectric constant and loss tangent. The pyroelectric properties were studied in poled and short circuit condition from 30°C to 700°C. The results obtained were discussed in the light of dielectric and conductivity properties of the samples.     

Enhanced energy storage in Sn-doped sodium bismuth titanate lead-free relaxor ferroelectric ceramics

Journal of Materials Science: Materials in Electronics - SnO2-doped (Bi0.5Na0.5)0.93Ba0.07TiO3 (BNT7BT) ceramics were prepared via a conventional solid-state reaction method. Their phase...     

Ferroelectric properties of barium calcium titanate ceramics doped with bismuth oxide

Ferroelectric properties of Bi doped (Ba_1 − xCa_x)_0.925Bi_0.05TiO₃ (Bi-BCT, 0.10 < x < 0.30) ceramic prepared by the solid-state technique have been studied. An interesting double-like hysteresis (P-E) loop at room temperature (300 K) with the remarkable linear dielectric response was observed over a certain electric field range. Room temperature P-E loops before and after de-aging, as well as those at different values of field cycling, could exclude the possibility that the double P-E loops might result from the antiferroelectric components and the electric field induced paraelectric-ferroelectric (PE-FE) transition near Curie temperature (T_c) in Bi-BCT, and verify that there exists a diffusional aging effect in Bi-BCT. A symmetry-conforming short-range ordering (SC-SRO) of point defects is suggested to be responsible for the observations of the interesting double-like P-E loop in Bi-BCT.     

Effect of novel (Gd,Cu) substitution on the electrical properties and magnetoelectric coupling of bismuth ferrite ceramics

The influence of Gd dopant and (Gd, Cu) dopants on the ferroelectric, dielectric and magnetoelectric properties of single phase BiFeO₃ (BFO) were investigated. Nanoparticles of undoped BiFeO₃, Bi_0.95Gd_0.05FeO₃ and Bi_1?xGd_xFe_0.98Cu_0.02O₃ (x?=?1, 2, 3, 4 and 5%) were prepared by sol–gel method. X-ray diffraction reveals that all the samples crystallize in rhombohedral phase. The simultaneous Gd and Cu doping at BFO lattice has significantly enhanced the ferroelectric properties of BFO compared to that of BFO. Substitution of Gd alone at the Bi site, gave rise to attractively enhanced remnant polarization. Though the (Gd, Cu) doped BFO samples exhibit relatively less enhancement, their values of remnant polarization are appreciable. Doping of (Gd, Cu) in the BFO lattice leads to an appreciable dielectric properties. An effective magnetoelectric coupling has been recorded for doped BFO when compared to BFO.     

The effect of processing variables on the mechanical and electrical properties of barium titanate positive-temperature-coefficient-of-resistance ceramics

The effect of processing variables on the mechanical and electrical properties of barium-titanate positive-temperature-coefficient-of-resistance (PTCR) ceramics has been studied. In the first part of this investigation the effect of changes to processing prior to sintering have been compared. This has highlighted the importance of slow compaction rates and the presence of soft agglomerates in the preparation of strong compacts. The addition of a binder prior to milling has been found to improve the strength of the sintered material by up to 50% by encouraging the formation of smaller, less damaging, pores. Strength, measured by diametral compression of discs, was found to be highly dependent on the density of the ceramic. Typically, the presence of a 22% porosity leads to a 75% reduction in strength compared to samples containing only a 1% porosity. No systematic effect of grain size on strength was observed.     

Effect of simultaneous substitution of magnesium and niobium on dielectric properties and phase transition temperature of bismuth sodium barium titanate ceramics

(Bi_1/2 Na_1/2)_0.94Ba_0.06Ti_1?x (Mg_1/3Nb_2/3) _x O₃ ceramic samples with x = 0.0, 0.01, 0.05, 0.15, 0.20 were synthesized by solid state method. Microstructure, dielectric properties, impedance and conductivity of the ceramics were studied. Phase formation was confirmed by X-ray diffraction. Co-doping of the ceramics with Mg and Nb at x = 0.01 raised the dielectric constant from 6510 to 8225 at the frequency of 1 KHz. Further increase in (Mg_1/3Nb_2/3)⁴⁺ concentration up to 0.15 increased the transition temperature from 275 °C to 339 °C and lowered the dielectric constant. The ac impedance measurements showed a linear response with frequency at lower temperature indicating insulating behavior and a single semicircular arc with spike at higher temperature.     

Ce-doped bismuth ferrite thin films with improved electrical and functional properties

Bi_1?xCe_xFeO₃ (BCFO) thin film capacitors (x = 0 to 0.2) are fabricated on indium tin oxide coated corning glass substrate by chemical solution deposition method. X-ray diffraction results show a partial phase transition from rhombohedral to tetragonal structure induced in BCFO thin film having preferred (110) orientation with increase in Ce dopant concentration. Current density–field (J–E) characteristics indicate that the leakage current density reduces by several orders of magnitude in Ce-doped BFO thin films resulting from smaller grain sizes and smoother surfaces. Space-charge-limited current and Fowler–Nordheim tunneling are identified as dominating leakage behavior in BCFO thin film capacitors at moderate and high field regions, respectively. Enhanced ferroelectric response with well-saturated (P–E) hysteresis loop is observed for Bi_0.88Ce_0.12FeO₃ thin film having high remnant polarization (P _r—127 µC/cm²) at an applied field of 1080 kV/cm. Bi_0.88Ce_0.12FeO₃ thin film exhibiting well-defined capacitance–field (C–E) butterfly loop with dielectric loss (tan δ—0.03) measured at 10 kHz suggested good ferroelectric properties with high tunability of about 88 %.     

The microstructure developments and electrical properties of calcium-modified barium titanate ceramics

The microstructure and electrical behaviour of calcium-modified BaTiO₃ ceramics of compositions (a) (Ba_1-x Ca _x )TiO₃, (b) Ba(Ti_1-x Ca _x )O_3-x and (c) (Ba_1-x/2Ca _x/2) (Ti_1-x/2Ca _x/2) O3_3-x/2 have been investigated. These characteristics are observed to vary systematically with the cationic ratio, = (Ba + Ca)/Ti, rather than the amount (x-value) and sites that Ca²⁺ ions are supposed to occupy. A large uniform grain microstructure and normal dielectric behaviour are obtained for 1.01 samples (groups I and II), whereas an ultra-fine grain microstructure and diffuse phase transformation (DPT) characteristics are observed for 1.08 samples (groups III). The latter is proposed to be the suppression of tetragonal to cubic transformation due to the formation of second phase. When the sintering atmosphere is changed from air to H₂/N₂ mixture, the electrical resistivity decreases and dielectric loss increases tremendously for = 0.99 samples (groups I), whereas the high electrical resistivity and low dielectric loss characteristics are preserved for 1.01 samples (groups II and III). The mechanism by which the cationic ratio improves the resistance of the materials to a reducing atmosphere is proposed to be the formation of hexagonal BaTiO_3- phase which consumes the oxygen vacancies generated.     

Preparation and electrical properties of semiconducting strontium—lead titanate PTCR ceramics

A typical positive temperature coefficient of resistance (PTCR) effect in yttrium-doped (Sr, Pb)TiO₃ ceramics made by chemical processing was obtained for the first time. The results show that the room temperature resistivity is lower than 10² Ω cm and the resistivity jump is above 10⁶. The breakdown voltage is above 340 V mm⁻¹ (a.c.). The sintering temperature is about 1100°C, lower than for conventional BaTiO₃ ceramics. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Characteristics of yttrium substituted sodium bismuth titanate thin films

Sodium bismuth titanate (NBT) thin films substituted with yttrium for Na site were prepared by a modified sol-gel processing and their dielectric properties were investigated. The stability of perovskite structure was highly affected by the amount of Y substitution and the annealing temperatures. Y substituted NBT thin films post-annealed at 750 °C exhibited uniform microstructures associated with grain growth inhibition. Relative permittivity and remnant polarization were maximized at 5 mol% Y substitution and loss tangents for all the prepared films were relatively stable with less than 0.03. It was also found that the substitution of yttrium led to the enhancement of diffuse phase transition for the NBT thin films.     

Optical and electrical properties of multiferroic bismuth ferrite thin films fabricated by sol-gel technique

Single-phase multiferroic BiFeO₃ thin films have been prepared on LaNiO₃/Si(100) and Si(100) wafer via sol-gel technique. The films are polycrystalline with preferring orientation of (101). The film has a conspicuous absorption in the blue and green light region, and band gap of 2.74 eV. The refractive index and the extinction coefficient of the film is about 2.36 and 0.06 at 600 nm, 2.26 and close to zero in the range of 800-1200 nm, respectively. The films also exhibit favorable ferroelectric and dielectric properties. A large photo induced open-circuit voltage was observed, indicating that the film exhibits photovoltaic behaviours.     

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.