Key Engineering Materials Vols. 368-372

Abstract: The spark plasma sintering technique was used to fabricate ceramics from Pb(Mg1/3Nb2/3)O3– PbTiO3 ceramic layers which were prepared by tape casting and TGG method used BaTiO3 templates as seeds. During heat treatment, epitaxial grain growth occurred on the BaTiO3 surfaces and formed <001> textured lead magnesium niobate-lead titanate, Pb(Mg1/3Nb2/3)O3-0.325PbTiO3 (PMN-32.5PT) ceramics. The phase compositions and microstructure were investigated. The results indicated that this method was an alternative sintering technology to synthesize dense lead-based relaxor ferroelectric ceramics.

Abstract: Relaxor-based ferroelectrics, 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (PMN-PT) with a pyrochlore-free phase, was prepared by a modified polymerized complex process. The reactive columbite (MgNb2O6) phase was synthesized by the polymerized complex method at 1050oC for 4 h with 3wt% excess MgO. Lead acetate and tetrebutyl titanate were used to synthesize pyrochlore-free PMN-PT powder via the columbite route, from 800oC to 900oC, in air for 4 h. X-ray diffraction and scanning electron microscopy were used to detect the perovskite phase evolution and the presence of the pyrochlore phase in PMN-PT. The formation of perovskite PMN-PT is a function of the time and temperature conditions of the precursor calcinations, and an optimum condition for the thermal decomposition of the precursor was determined to avoid the formation of the pyrochlore phase.

Abstract: Dielectric properties and structural morphology of the Sc2O3 free and reduced lead content piezoelectric ceramic system, (1-x)Bi(Mg1/2Zr1/2)O3-xPbTiO3 (BMZ-xPT), were investigated in this study. The average grain size of the fresh fractured surfaces was of the order of ≤1 μm to ∼3 μm. The dielectric constant, loss tangent, Curie temperature, remnant polarization, coercive field, piezoelectric coefficient, and the planer coupling constant of ceramics in the vicinity of the morphotropic phase boundary (MPB) (x∼0.55) were, ∼1450, 0.0952, ∼553 K, 29 (μC/cm2) , 23 (kV/cm), ∼185 pC/N, and ∼30%, respectively. It was observed that with decreasing PbTiO3 contents the phase transition anomaly became broadened. The position of the dielectric constant maximum (ε′max) did not show any significant variation with probe frequency, exhibiting character of diffuse phase transition like many other disordered perovskites.

Abstract: We present Mg and Ti co-doped NiO-based polycrystalline ceramic with high-permittivity dielectric properties. Analysis of the ceramic’s microstructure and composition proves that obvious grain boundaries NiTiO3 are formed. The measurements of frequency and temperature dependence of impedance and dielectric permittivity indicate that the grain and grain boundaries have remarkable influence on the dielectric properties due to the various activation energies.

Abstract: Several glass compositions with high electrical resistivity were developed and added to the barium titanate ceramics. The glass additions were found to greatly increase the breakdown strength of the composite ceramics which has a 0-3 connectivity. The electrical properties of the liquid phase sintered ceramics are sensitive to the variations of the volume fraction and connectivity of the glass phase.

Abstract: Ultrafine-grained ceramics based on nano-scale barium titanate for BME-MLCC applications have been prepared. Relationships of milling time, microstructures and dielectric properties have been investigated. With processing selected carefully, the present ceramics show ultrafine grain size (180nm) and homogeneous microstructures, well with high dielectric constant (ε25=2550), low dielectric loss (<0.02), high resistivity, high breakdown field and X7R temperature specifications, which would be promising materials for the next generation BME-MLCC applications.

Abstract: BaTiO3 films with a thickness up to 3 μm were fabricated under the hydrothermal conditions. It was found that the crystallinity of BaTiO3 increases with the concentration of Ba(OH)2 solutions. Along with the increasing of time, the crystallinity of BaTiO3 increases, reaches the maximum value and then decreases. The measured values of remanent polarization (Pr) and coercive field (Ec) are 1.74μC/cm2 and 24KV/cm. The leakage of the films at 1V is 10-7A/cm2. The dielectric constant and loss tangent of hydrothermal derived BaTiO3 film at a frequency of 1 KHz were 600 and 0.2, respectively.

Abstract: Barium strontium titanate, BST (BaxSr1-xTiO3), nanoparticles were prepared by a sol-gel hydrothermal technique. BST powders of different composition (x=0.1, x=0.3, x= 0.5, x=0.7, x=0.9) prepared by sol-gel technique previously were treated by hydrothermal synthesis method later. XRD results indicated that the as-prepared perovskite BST nanoparticles have the accurate proportioning composition. These results showed that the combination of sol-gel and hydrothermal technique would become a potential and promising process for fabricating BST and other nanopowders.

Abstract: Ba0.6Sr0.4TiO3 nanopowders (~ 80 nm in size) were prepared by low temperature hydrothermal process. The process and synthesis mechanism were discussed in detail. Furthermore, the powders were pressed into disc-shaped pellets and sintered at different temperatures. The frequency dependence of the dielectric constant and loss angle tangent of the sintered BST ceramics are measured from room temperature to 500°C and a diffuse dielectric anomaly by the dielectric relaxation was found.

Abstract: Barium strontium titanate (Ba1−xSrxTiO3, BST) films have been prepared on Pt/Ti/SiO2/Si by medium frequency (MF) magnetron sputtering, and subsequently in situ crystallized at 500-700°C. The microstructures of the MF-BST films are studied. BST films prepared by radio frequency (RF) magnetron sputtering and exhibited preferential (110) orientation, are compared. XRD shows that the MF-BST films exhibit preferential (111) orientation and better crystallization than the RF-BST films at the same annealing temperature. AFM displayed that the MF-BST films were smooth and compact. XPS analysis exhibited that the MF-BST films revealed better surface and interface structural characteristics. Their dielectric properties were also compared.