The effect of glass addition on the dielectric properties of barium strontium titanate

Ba_0.7Sr_0.3TiO₃ (BST) ceramics were prepared by the conventional solid state ceramic route. Different weight percentages of twelve different glasses were added to the calcined BST ceramics and sintered. The structure and microstructure of the sintered materials were investigated by X-ray diffraction and Scanning Electron Microscopic techniques. The low frequency dielectric properties of the glass-ceramic composites were measured using LCR meter. Some of the glasses improved the dielectric properties and considerably lowered the sintering temperature. The glasses were prepared and characterized under identical conditions. Among the different glasses, 1.5 wt% addition of 71ZnO–29B₂O₃ lowered the sintering temperature of BST to 975 °C with a dielectric loss of 9 × 10⁻³ and dielectric constant of 875 at 1 MHz. The curie temperature of BST ceramics was found to shift towards lower temperature with glass addition.     

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.     

ZnO掺杂对CLST微波介质陶瓷烧结及介电性能的影响

研究了烧结助剂ZnO对CaO-Li2O-Sm2O3-TiO2(简写为CLST)系微波介质陶瓷的烧结特性及介电性能的影响.结果表明:ZnO的添加能有效地降低CLST陶瓷的烧结温度至1150℃.掺杂2wt%ZnO的CLST陶瓷取得了较好的介电性能:εr=84,tanδ=0.009,τf=-15ppm/℃.     

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.     

Effect of fluoride doping on impedance spectra of barium strontium titanate glass ceramics

A system of barium strontium titanate glass ceramics with different fluoride concentrations were prepared by melt-annealing technique. The effect of fluoride doping on impedance spectra of the barium strontium titanate glass ceramics were investigated. According to the impedance spectroscopy studies, three (low, middle, and high frequency) electrical responses, which corresponds to glass phase, crystal–glass interface and crystal interior were identified. It is shown that with the increase of fluoride concentration, the resistivity of the glass phase passed through a minimum and then increased. In addition, the capacitance of the crystal–glass interface increased and the capacitance of the crystal phase decreased with the increase of the fluoride concentration. Moreover, as a result of ac conductivity calculation and analysis, it is believed that the dc conduction was affected by the glass and crystal–glass interface regions and ac regime was attributed to the crystal phase. Based on the results, a change of the compensation mechanism from electronic to ionic one with variation in fluoride concentration was proposed.     

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.     

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.     

Influence of stoichiometry and impurity on the sintering behaviour of barium titanate ceramics

The influence of stoichiometry, i.e. Ba/Ti ratio, and impurity on the densification of BaTiO₃ were investigated. The BaTiO₃ powders were prepared by conventional calcination of BaCO₃ and TiO₂. The stoichiometric ratios (Ba/Ti) were in the range 0.99 to 1.005. Impurity effects on the sintering behaviour were investigated with different purities of raw powders. The sintering behaviour of BaTiO₃ has been studied extensively but an understanding of stoichiometric effects on densification is still incomplete. An excess of TiO₂ lowered the onset temperature of sintering (initial state of sintering — 3% shrinkage). These results indicate that stoichiometric variation of BaTiO₃ affects the initial state of sintering. The rate of densification for a Ti-rich sample was considerably faster than that for a Ba-rich sample. It was a so-called activated sintering. The TiO₂ excess reacts with BaTiO₃ to form Ba₆Ti₁₇O₄₀, which forms with BaTiO₃ a eutectic melt at 1320 °C. The liquid phase, however, enhanced grain growth, not densification.     

Effect of nanometer barium titanate powders on the dielectric properties of X7R ceramics

High dielectric constant X7R dielectric materials were prepared by doping with nanometer BaTiO₃ additives, with a dielectric constant as high as 5,400 and dielectric loss lower than 1.0% at 25 °C, when they were sintered at 1,240 °C for 4 h. The effects of nanometer BaTiO₃ additives on the microstructure and dielectric properties of X7R ceramics were investigated in this paper. The nanometer BaTiO₃ additives were prepared by sol–gel method with an average particle size of ~65 nm. It was favorable by nanometer BaTiO₃ additives to make the ceramics hold high dielectric constant and still satisfy the requirement of EIA X7R specification. Due to the special nano-effect of the nanometer BaTiO₃ additives, the densification of ceramics were promoted effectively, which resulted in the increase of dielectric constant. The temperature-capacitance characteristics which satisfied X7R specification were attributed to the formation of abundant “core–shell” structure, which gave rise to the abundant spontaneous polarization microarea and the decrease of the tetragonality (c/a ratio).     

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.     

Copper oxide as a sintering agent for barium titanate based ceramics

The purpose of this work was to study the effect of CuO as a versatile sintering agent for BaTiO₃ based ceramics. The response is shown to exist in three directions. Firstly, as liquid-phase former at comparatively low temperatures. Hence, the influence of various CuO-based flux formers on the shrinkage behaviour and the microstructure development of the ceramics was investigated. Secondly, the aptitude as an internal susceptor for secondary phase initiated microwave sintering. The use of CuO as a lossy secondary phase leads to an accelerated microwave heating of the ceramics. Thirdly, the addition of CuO to BaTiO₃ powders with Ba-excess results in a phase transition cubic hexagonal at about 1300°C, which is a indication for the incorporation of Cu²⁺ ions into the BaTiO₃ lattice at Ti sites under this conditions.     

Influence of Sr/Ba ratio on the energy storage properties and dielectric relaxation behaviors of strontium barium titanate ceramics

Sr _x Ba_1?x TiO₃ (x = 0.50–0.70) ceramics were prepared by conventional solid-state method. The effects of Sr/Ba ratio on the microstructures, energy storage properties and dielectric relaxation behaviors of ceramics were systematically investigated. Scanning electron microscopy observations revealed that the grain size was inhibited with increasing Sr molar fraction. The Sr_0.6Ba_0.4TiO₃ ceramics obtained the highest energy density of 0.3629 J/cm³ attributed to the increase of average breakdown strength resulting from the decrease of grain size and the optimizing of microstructure. In order to investigate the influence of Sr/Ba ratio on the dielectric relaxation behaviors, the activation energy has been calculated from the relaxation of dielectric loss and the complex impedance spectra by the Arrhenius relationship, respectively. The same results indicated that the decrease of grain size resulting in more grain boundaries, it was difficult for transferring charge and making an orientation under external electric field. Meanwhile, more defects existed at grain boundary and accelerated the thermally activated motions of defects, leading to the increase of activation energy.     

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.     

Semiconducting barium titanate ceramics prepared by using yttrium hexaboride as sintering aid

Nb-doped BaTiO₃ semiconducting ceramics have been prepared at 1150 °C by employing YB₆ as the sintering aid. The low-temperature sintered samples exhibit a positive temperature coefficient of resistivity (PTCR) effect. The room-temperature resistivity and the magnitude of PTCR effect depend on the amount of YB₆ added, the Nb₂O₅ content and the sintering conditions. At 1 mol% of YB₆, the sample has a low room-temperature resistivity and a resistivity jump of about 10⁴. Transmission electron microscope studies revealed that the intergranular region between the crystalline BaTiO₃ grains has an amorphous structure. Y, Ba and Ti are present in the intergranular region but no Y is detectable in the crystalline grains. A liquid phase is believed to be present during sintering and it helps to facilitate the densification process and to enhance the PTCR effect.     

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.     

Strength and toughness of barium titanate ceramics

The effect of processing variables on the mechanical and electrical properties of holmium-doped barium titanate ceramics with a positive temperature coefficient of resistance has been investigated. This paper contains details of the tests used to measure the mechanical properties of ceramics prepared using four compositional mixes. Two methods of measuring strength were used: diametral compression of disc samples and four-point bending of beam specimens. Fracture toughness was also evaluated using two methods: the failure of single edge-notched (SEN) beams under four-point loading and cracking from a surface indentation with a diamond pyramid indentor. Values of strength ranged from 18 to 82 MPa for the four materials when measured by the diametral compression test. This compared with a range of 35–79 MPa for the same materials tested in pure bending. Fracture toughness values ranged from 0.65 to 0.95 MPa m^1/2 for the SEN specimens and from 1 to 1.8 MPa m^1/2 using the indentation technique on the same samples.     

High density sintering of pure barium titanate

The techniques of slow sintering, addition of a volatile flux, and grain growth inhibition have been used to produce high density sintering in pure barium titanate. The use of carbon as grain growth inhibitor gave a density of 99% theoretical at 0.7m grain size. This technique may be used for other suitable ceramics, when the proposed application requires improved physical properties. An extension of the procedure gives a range of electrically conducting ceramics.