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.     

Effect of Fe and Fe-Ba substitution on the piezoelectric and dielectric properties of lead zirconate titanate ceramics

Polycrystalline samples of Fe and Fe-Ba doped lead zirconate titanate (PZT) ceramics near the morphotrophic phase boundary have been synthesized by a solid-state reaction technique. Preliminary X-ray analysis of the compound confirms that there is no change in the crystal structure of PZT on co-doping with Fe and Ba. The maximum mechanical quality factor Q_m was found to be 1000 for Fe doped material and 880 for Fe-Ba doped material. The electromechanical coupling factor for Fe and Fe-Ba doped samples were 0.535 and 0.495 respectively. The corresponding values for the piezoelectric charge constant d₃₃ were 135 and 250 pC/N respectively. These results are discussed in terms of position occupied by dopants in to the lattice and their corresponding microstructures. These Fe-Ba doped PZT materials could be likely candidates for high power ultrasonic and underwater SONAR transducer systems.     

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.     

Structural and dielectric properties of La-doped lead titanate ceramics

(Pb_1−xLa_x)TiO₃ (PLT) ceramics of perovskite type were prepared by sol-gel process, and their structural and dielectric properties investigated. The obtained compounds crystallize, under heat treatment, at relatively low temperatures and no secondary phases have been observed on the corresponding XRD spectra. Annealing temperature (T_a) and its duration (t_a) appear to influence notably their structural and dielectric characteristics.     

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.     

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.     

The relationship between the microstructure and microwave dielectric properties of zirconium titanate ceramics

Zirconium titanate (ZrTiO₄) ceramics have been prepared by the mixed oxide route using small additions of ZnO, Y₂O₃ or CuO. Specimens were sintered mainly at 1400 °C and cooled at various rates: water-quench, air-quench, 300 °C h^–1, 120 °C h^–1, 6 °C h^–1 and 1 °C h^–1. Products prepared with additives exhibited densities of at least 93% of the theoretical value. As the cooling rate after sintering was decreased, the length of the lattice parameter in the b direction was reduced and transmission electron diffraction revealed superlattice reflections associated with cation ordering. For specimens cooled at 1 °C h^–1, electron diffraction patterns exhibited features consistent with an incommensurate superstructure in the a direction. The dielectricQ value of rapidly cooled (air-quenched) ceramics was 2000 at 5 GHz. With an increase in the degree of cation ordering theQ value increased to a maximum of 4400 for specimens cooled at 6 °C h^–1. For specimens cooled at the slowest rate (1 °C h^–1) theQ value fell to 2000 due in part to the presence of microcracks and exsolved ZrO₂. Diffusion of trivalent impurities (yttria) into the host ZrTiO₄ grains also led to a lowering of theQ values.The microwave dielectric properties of zirconium titanate ceramics are sensitive to processing conditions and mircrostructural features. The highestQ values (lowest loss) should be achieved in homogeneous specimens, free of trivalent impurities and lattice defects, in which lowQ-value second phases, microcracks and pores are eliminated.     

Temperature behavior of dielectric and piezoelectric properties of samarium-doped lead titanate ceramics

The dielectric and electromechanical coupling properties of Sm-doped and Mn-doped PbTiO(3) ceramics were investigated from 4.2 to 300 K. The upper and lower limits of the ceramic dielectric and piezoelectric properties were calculated by averaging the single-domain constants that were determined from a phenomenological theory. Comparisons of the measured and calculated properties were then made. The measured dielectric permittivity epsilon(T)(33) and piezoelectric strain coefficient d(33) appear to be mainly due to the averaging of the intrinsic single-domain response. The large piezoelectric and electromechanical anisotropies present in modified PbTiO(3) ceramics also appear to be an intrinsic property of the material. The piezoelectric coefficient d(31), as well as the planar coupling coefficient k(p), was found to have very small values over two temperature regions, from 120 to 170 K and from 240 to 270 K.     

Influence of samarium doping on structural and dielectric properties of strontium bismuth tantalate ceramics derived by molten salt synthesis route

Layered Sr(Bi_1?xSm_x)₂Ta₂O₉ ceramics with x ranging from 0 to 0.10 (10 mol%) were fabricated by the low temperature molten salt synthesis route. X-ray powder diffraction studies revealed that the single phase orthorhombic layered perovskite structure is retained in all these compositions. Scanning electron microscopic studies on these ceramics confirmed the presence of well packed equiaxed plate shaped grains. The dielectric and electrical conductivity properties were studied in the 100 Hz–1 MHz frequency range at 300 K. Interestingly, the 10 mol% samarium doped SrBi₂Ta₂O₉ ceramics exhibited high dielectric constant (ε_r = 155) and low dielectric loss (0.00298) compared to those of other compositions. The electrical conductivity of undoped and samarium doped ceramics increased linearly with increase in frequency.     

Effect of phosphor doping on the microstructure and dielectric properties of barium titanate ceramics

The effect of phosphor doping on the sintering behaviour, microstructure and dielectric properties of BaTiO₃ has been investigated. Diisopropyl phosphinate is added to high-purity BaTiO₃ powder prepared by the wet chemical method with a final amount of 0.14 wt.% P₂O₅ with respect to the BaTiO₃. Phosphor-doped BaTiO₃ ceramics with a high density and uniform grain size have been produced by using wet processing and pressureless sintering without any binder. A scanning electron microscope, thermometric analysis, X-ray diffraction and an impedance analyser have been used to determine the microstructure as well as the dielectric properties. The phosphor cations can form a liquid phase belonging to the ternary system BaO-TiO₂-P₂O₅, leading to the formation of BaTiO₃ ceramics with high density at low temperature. Phosphor-doped BaTiO₃ ceramics with a high density of 96% D_th are obtained by sintering at 1200°C with a soaking time of 2 h. The dielectric constants of samples sintered at 1150 and 1200°C are as high as 6100 and 5500, respectively; the Curie temperature of samples decreases with decreasing sintering temperature. Doping with a small amount of phosphor can improve the sintering and dielectric properties of BaTiO₃ ceramics.     

Effects of Ca and Sr substitution on dielectric properties in ceramics

Modification of dielectric characteristics for Ba₃Sm₃Ti₅Ta₅O₃₀ was performed by Ca and Sr substitution for Ba. The temperature coefficient of the dielectric constant () of Ba₃Sm₃Ti₅Ta₅O₃₀ decreased somewhat by Ca substitution, but the dielectric constant () decreased considerably. In the case of Sr substitution, the temperature coefficient could be markedly decreased without considerable decrease of dielectric constant. Ceramics of the two series could obtain dielectric properties of high (> 100) and low loss (10^–3 at 1 MHz).     

Effects of Nd substitution on the polarization properties and electronic structures of bismuth titanate single crystals

Single crystals of Nd-substituted Bi₄Ti₃O₁₂ ferroelectrics were grown by a self-flux method, and the effects of Nd substitution on the polarization properties and optical transmission spectra of the crystals have been investigated. Bi_3.52Nd_0.48Ti₃O₁₂ crystals showed a smaller remanent polarization along the a axis of 29 μC/cm² than Bi₄Ti₃O₁₂ crystals (46 μC/cm²), and this result is in good qualitative agreement with the calculation of the spontaneous polarization based on Rietveld analysis of neutron diffraction. Electronic band structure calculations using the structural data suggest that the orbital hybridization between the Nd 5d and O 2p states stabilizes oxide ions in the perovskite layers, which is consistent with the much smaller leakage current observed for Nd-substituted crystals.     

Ferroelectric and dielectric properties of sol-gel processed barium titanate ceramics and thin films

Ferroelectric and dielectric properties of barium titanate (BaTiO3) bulk ceramics and thin films have been investigated. The bulk ceramics and thin film samples have been prepared from barium acetate [Ba(CH3COO)2] and titanium(IV)isopropoxide [Ti(CH3)2CHO)4] precursors by sol-gel technique. The as-grown bulk powder and thin films were found to be amorphous, which crystallized to tetragonal phase after annealing at 700°C in air for one hour. The values of the spontaneous polarization (Ps), remanant polarization (Pr) and coercive field (Ec) of the bulk ceramics were found to be 19.0, 12.6 C cm–2 and 30 kVcm–1 respectively. In the case of the film, the values of Ps, Pr and Ec were respectively found to be 14.0, 3.2 Ccm–2 and 53 kVcm–1. The capacitance-voltage (C-V) characteristics of the film also showed polarization hysteresis. The values of the dielectric constant () of the bulk ceramic and thin film at 1 kHz were found to be 1235 and 370 respectively. Both the films and ceramics showed dielectric anomaly peaks at 125°C, showing ferroelectric to paraelectric phase transition.     

Effect of Gd-substitution on dielectric and transport properties of lead zirconate titanate ceramics

The gadolinium (Gd)-modified lead zirconate titanate (i.e., Pb_1?xGd_x (Zr_0.65Ti_0.35)_1?x/4O₃; x = 0, 0.07, 0.10 and 0.12) ceramics have been synthesized using a high-temperature (~1,100 °C) solid-state reaction route. Preliminary X-ray structural studies show the formation of single-phase compounds in the tetragonal crystal system. Scanning electron micrographs of the surface of pellet samples show uniform distribution of grains of different shape and size with few voids. It is interesting to observe the significant effect of Gd-substitution on the nature, size, and distribution of grains, and the density of samples. Detailed analysis of dielectric properties of the materials indicates that the materials are non-relaxor but have diffused ferroelectric phase transition. The temperature and frequency dependence of conductivity follows Jonscher’s universal power law.     

改进的sol-gel工艺制备细晶Ba0.6Sr0.4TiO3陶瓷及其介电性能的研究

用改进的sol-gel工艺制备了细晶钛酸锶钡(Ba0.6Sr0.4TiO3,BST)陶瓷块体,研究了BST陶瓷的结晶与介电性能.在这种改进sol-gel的工艺中,用传统的固相反应煅烧形成BST粉体,经高能球磨制备BST纳米陶瓷粉体,再将一定质量的纳米粉体加入到相同化学组成的BST的溶胶液中,经普球球磨12h后,制备成悬浮性好,分散均匀的浆料.浆料可用来制备BST陶瓷,并在1200℃保温2h烧结成瓷,结果显示,BST陶瓷块体结构致密,晶粒尺寸在0.15～2μm之间.分析了样品的介电性能和晶粒尺寸对材料介电性能的影响.介电温谱显示,在0℃,100kHz时,相对介电常数为2500,介电损耗为0.02;并且存在明显的弥散相变.     

Synthesis,structure and electrical studies of praseodymium doped barium zirconium titanate

Praseodymium (Pr) doped barium zirconium titanate with nominal composition (Ba_1−xPr_x)(Zr_0.52Ti_0.48)O₃ (x = 0.1 and 0.2) were synthesized using solid state reaction method. X-ray analysis conform the formation of cubic phase Pr-doped barium zirconium titanate along with minor pyrochloric phase. The increase in grain size after primary investigation reveals the influence of Pr ions on the domain structure and its microstructure. In order to correlate the effect of the chemical composition with the conduction mechanism, different AC electrical parameters have been addressed. The frequency dependant tangent loss of the sample was less for both the ceramics. The temperature dependence results show that the dielectric parameters and resistivity increases as Pr-content in the ceramic increases; this is attributed to the grain size and dipole dynamics. Complex impedance (Z*) plots show frequency dependent behavior as the response for the grain resistance mechanisms. This mechanism has been represented by an equivalent circuit. The temperature dependence of the electrical conductivity and Seebeck coefficient showed n-type non-degenerated semiconductor in the measured temperature range. The temperature dependent conductivity measurement suggests a novel negative temperature coefficient of resistance behavior of the samples. Furthermore, the frequency dependent conductivity plot shows increasing behavior.