Study of the dielectric and ferroelectric properties of chemically processed BaxSr1-xTiO3 thin films

Polycrystalline BaxSr1-xTiO3 (x = 0.4 and 0.8) thin films with a perovskite structure were prepared by the polymeric precursor method on a platinum-coated silicon substrate. High-quality thin films with uniform composition and thickness were successfully produced by dip-coating and spin-coating techniques. The resulting thin films prepared by dip and spin-coating showed a well-developed dense polycrystalline structure with uniform grain size distribution. The metal-BST-metal structure of the thin films displays good dielectric and ferroelectric properties. The ferroelectric nature to BaxSr1-xTiO3 (x = 0.8) thin film, indicated by butterfly-shaped C-V curves and confirmed by the hysteresis curve, showed 2P(r) = 5.0 muC/cm(2) and E-c = 20 kV/cm. The capacitance-frequency curve reveals that the dielectric constant may reach a value of up to 794 at 1 kHz. on the other hand, the BaxSr1-xTiO3 (x = 0.4) thin films had paraelectric nature and dielectric constant and the dissipation factor at a frequency of 100 kHz were 680 and 0.01, respectively, for film annealed at 700 degreesC. In addition, an examination of the film's I-V curve at room temperature revealed the presence of two conduction regions in the BaxSr1-xTiO3 (x = 0.4 and 0.8) thin films, showing ohmic-like behavior at low voltage and a Schottky-emission or Poole-Frenkel mechanism at high voltage. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Microstructure of organometallic derived PLZT ceramics

The PLZT powders with the formula Pb0.905La0.095(Zr0.65Ti0.35)(0.976)O-3+3.5 wt.% PbO were prepared by the organometallic precursor method (Pechini and partial oxalate processes). The microstructure of sintered 9.5/65/35 PLZT ceramics obtained from a partial oxalate procedure shows that the outstanding feature of this microstructure is its fairly uniform grains of about 1.8 mum. The microstructure of sintered PLZT ceramics obtained by the Pechini process consists of uniform small randomly- oriented grains tightly bonded together in the central part of the sample with,a grain size of about 1.2 mum. Cubic and elongated grains are formed at the sample's border. The microstructures of hot pressed PLZT ceramics obtained from both processes are dense and rather uniform. After a double stage of hot pressing (2 plus 20 h) the microstructure of PLZT is fully dense, uniform and homogeneous with a grain size of approximately 2.5 mum. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

AC impedance study of Ni, Fe, Cu, Mn doped ceria stabilized zirconia ceramics

Doped zirconia has been used in electronic applications in the cubic crystalline phase. Ceria-stabilized tetragonal zirconia presents high toughness and can also be applied as solid electrolytes. The tetragonal phase of zirconia can be stabilized at room temperature with ceria in a broad range of composition. However, CeO2-ZrO2 has low sinterability. so it is important to investigate the effect of sintering dopants. In this study the effect of iron, copper. manganese and nickel was investigated. The dopants such as iron and copper lowered the sintering temperature from 1600 degreesC down to 1450 degreesC, with a percentage of tetragonal phase retained at room temperature higher than 98% and also with an increase of the electrical conductivity. The electrical conductivity was measured using impedance spectroscopy. The grain boundary contribution was determined and the activation energy associated with the ionic conduction was 1.04 eV. The dopants can also promote a grain boundary cleanliness verified by blocking effect measurement. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Microstructural and electric properties of bismuth-layered structured ceramics - SrBi2(Ta1-xNbx)O-9

Ceramic samples of SrBi2(Nb1-xTax)O-9 (0 less than or equal to x less than or equal to 1) were prepared by the solid state reaction method in order to investigate their structural and electrical features as well as obtain useful information to improve the properties of SrBi2(Nb1-xTax)O-9 as a thin film. The X-ray diffraction patterns and the scanning electronic microscopy photomicrographs show no secondary phases but the formation of a solid-state solution for all the composition. The ac conductivity of the samples, measured at 25 degreesC and 100 kHz frequency, decreases with the increase of Ta content. Such results were explained by intrinsic conductivity of pure components.

Low-voltage varistor based on (Sn,Ti)O-2 ceramics

A description is given of the nonohmic behavior obtained in (SnxTi1-x)O-2-based systems. A matrix founded on (SnxTi1-x)O-2-based systems doped with Nb2O5 leads to a low-voltage varistor system with nonlinear coefficient values of similar to9. The presence of the back-to-back Schottky-type barrier is observed based on the voltage dependence of the capacitance. When doped with CoO, the (SnxTi1-x)O(2)(.)based system presents higher nonlinear coefficient values (>30) than does the SnO2-based varistor system.

Effect of processing route on the phase formation and properties of Bi4Ti3O12 ceramics

Our efforts were directed to the preparation of bismuth titanate-Bi4Ti3O12 (BIT) by two procedures: mechanically assisted synthesis and polymeric precursor method to display a variety of their advantages. To follow the nucleation and phase formation of BIT, XRD and Rietveld refinement analysis were used and it was shown that Bi4Ti3O12 ceramic can been successfully prepared from nano-sized powders obtained by both methods. The ferroelectric properties were determined and the loops from BIT obtained by polymeric precursor method were not fully saturated with a remnant polarization of 20 mu C/cm(2) and coercitive field of 1500 kV/cm. BIT obtained from powders prepared by mechanically assisted synthesis shows a remnant polarization of 0.65 mu C/cm(2) and coercitive field of 1050 kV/cm. The grain morphology may be the factor causing the observed differences. (C) 2005 Published by Elsevier Ltd and Techna Group S.r.l.

WO3 and ZnO-doped SnO2 ceramics as insulating material

SnO2 ceramics doped with ZnO and WO3 were prepared by mixed oxide method. The effect of ZnO and WO3 additives could be explained by the substitution of Sn4+ by Zn2+ and W6+. The addition of WO3 inhibits the grain growth due to the segregation of SnZnWO8 and ZnWO6 at the grain boundaries without strong influence on the densification process. The electrical characterization (log E x log J) shows that the ternary system SnO2-ZnO-WO3 exhibits a very high resistivity of around 10(14) Omega M. Independently of the WO3 concentration, the electrical conductivity of the Sn02-ZnO-WO3 system is always lower than that of the undoped tin dioxide. (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Er3+ and Eu3+ containing transparent glass ceramics in the system PbGeO3-PbF2-CdF2

Glasses with composition 60PbGeO(3)-10PbF(2)-30CdF(2) (mol%) have been obtained in the bulk form with a high stability against crystallization. After doping them with 0.5 mol% of Er3+ or Eu3+ and appropriate heat treatment transparent glass ceramics could be obtained. Electronic spectroscopy, X-ray diffraction and transmission electron microscopy measurements have been made. beta-PbF2: Er3+/Eu3+ Single crystals, 5-10 nm in size, are detected in the otherwise transparent composite medium, the size of the particles and absence of clustering allowing for the increased transparency of the final materials. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Influence of strains and defects on ferroelectric and dielectric properties of thin-film barium-strontium titanates

Pristine, W and Mn 1% doped Ba(0.6)Sr(0.4)TiO(3) epitaxial thin films grown on the LaAlO(3) substrate were deposited by pulsed laser deposition (PLD). Dielectric and ferroelectric properties were determined by the capacitance measurements and X-ray diffraction was used to determine both residual elastic strains and defect-related inhomogeneous strains-by analyzing diffraction line shifts and line broadening, respectively. We found that both elastic and inhomogeneous strains are affected by doping. This strain correlates with the change in Curie-Weiss temperature and can qualitatively explain changes in dielectric loss. To explain the experimental findings, we model the dielectric and ferroelectric properties of interest in the framework of the Landau-Ginzburg-Devonshire thermodynamic theory. As expected, an, elastic-strain contribution due to the epilayer-substrate misfit has an important influence on the free-energy. However, additional terms that correspond to the defect-related inhomogeneous strain had to be introduced to fully explain the measurements.

Mechanochemical synthesis of ceramic powders with perovskite structure

The mechanical activation is one of the most effective method for obtaining highly disperse system due to mechanical action stress fields form in solids during milling procedure. This effect results in changes of free energy, leading to release of heat, formation of a new surface, formation of different crystal lattice defects and initiation of solid-state chemical reaction. The accumulated deformation energy determines irreversible changes of crystal structure and consequently microstructure resulting in the change of their properties. Mechanochemical processing route has been developed recently for the production of intermetallic and alloy compounds. The intrinsic advantage of this process is that the solid-state reaction is activated due to mechanical energy instead of the temperature. It was shown that the chemical reactivity of starting materials could be improved significantly after mechanochemical activation and, subsequently, the calcination temperature was reduced. Besides, it was apparent that the mechanochemical treatment could enhance the reactivity of constituent oxides; however, the sintering process could not be avoided to develop the desired ceramics. A novel mechanochemical technique for synthesis of fine-grained perovskite structured powders has shown that it is possible to form perovskite at room temperature. The effect of milling on the formation of perovskite structure of barium titanate (BT), lead titanate (PT), PZT, PZN, magnesium niobate (PMN) and LM ceramic materials was analyzed. The dielectric properties of sintered ceramics are comparable with those prepared by other methods in the literature. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Comparison of two bond strength testing methodologies for bilayered all-ceramics

Objectives. This study compared the shear bond strength (SBS) and microtensile (MTBS) testing methodologies for core and veneering ceramics in four types of all-ceramic systems.Methods. Four different ceramic veneer/core combinations, three of which were feldspathic and the other a fluor-apatite to their respectively corresponding cores, namely leucitereinforced ceramic ((IPS)Empress, Ivoclar), low leucite-reinforced ceramic (Finesse, Ceramco), glass-infiltrated alumina (In-Ceram Alumina, Vita) and lithium disilicate ((IPS)Empress 2, Ivoclar) were used for SBS and MTBS tests. Ceramic cores (N = 40, n = 10/group for SBS test method, N=5blocks/group for MTBS test method) were fabricated according to the manufacturers' instructions (for SBS: thickness, 3 mm; diameter, 5 mm and for MTBS: 10 mm x 10 mm x 2 mm) and ultrasonically cleaned. The veneering ceramics (thickness: 2 mm) were vibrated and condensed in stainless steel moulds and fired onto the core ceramic materials. After trying the specimens in the mould for minor adjustments, they were again ultrasonically cleaned and embedded in PMMA. The specimens were stored in distilled water at 37 degrees C for 1 week and bond strength tests were performed in universal testing machines (cross-head speed: 1mm/min). The bond strengths (MPa +/- S.D.) and modes of failures were recorded.Results. Significant difference between the two test methods and all-ceramic types were observed (P < 0.05) (2-way ANOVA, Tukey's test and Bonferroni). The mean SBS values for veneering ceramic to lithium disilicate was significantly higher (41 +/- 8 MPa) than those to low leucite (28 +/- 4 MPa), glass-infiltrated (26 +/- 4 MPa) and leucite-reinforced (23 +/- 3 MPa) ceramics, while the mean MTBS for low leucite ceramic was significantly higher (15 +/- 2 MPa) than those of leucite (12 +/- 2 MPa), glass-infiltrated (9 +/- 1 MPa) and lithium disilicate ceramic (9 +/- 1 MPa) (ANOVA, P < 0.05).Significance. Both the testing methodology and the differences in chemical compositions of the core and veneering ceramics influenced the bond strength between the core and veneering ceramic in bilayered all-ceramic systems. (c) 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Dielectric spectroscopy analysis of CaCu3Ti4O12 polycrystalline systems

Dielectric spectroscopy was used in this study to examine CaCu3Ti4O12 polycrystalline samples. The analysis involved systems presenting low non-Ohmic properties, and the grain's internal domain was evaluated separately from the contribution of barrier-layer capacitances associated with Schottky-type barriers in this type of material. The effect of oxygen-rich atmosphere and high cooling rate was evaluated, revealing a strong increase in the dielectric properties of the CaCu3Ti4O12 system under these conditions. This effect was attributed to a chemical change in the grain's internal domain, which may be considered an internal barrier-layer capacitance of the polycrystalline material. (c) 2006 American Institute of Physics.