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Small amounts of codoping La and Ga on the A and B sites of BaTiO3, respectively, resulting in a solid solution of the type Ba(sub{1-3x})La(sub 2x)Ga(sub 4x)Ti(sub {1-3x})Al(sub 4x)O(sub 3) are investigated. The resulting compounds exhibit a remarkable decrease in Curie temperature as well as a significant enhancement in the dielectric constant.

Small amounts of La and Al doping on the A and B site of BaTiO3, respectively, resulting in a solid state solution of the type Ba(sub{1-3x})La(sub 2x)Ti(sub{1-3x})Al(sub 4x)O(sub 3) are investigated. The Pechini process prepares the compositions.

Lead free potassium sodium niobate (K0.5Na0.5NbO3) ceramic powders were synthesized by colloidal coating method. The calcined powders (800°C) were sintered conventionally at three different temperatures (1050°C, 1100°C and 1150°C) and the effect of sintering temperature on density, microstructure, composition and electrical properties was investigated. All the samples showed a single phase perovskite structure with orthorhombic symmetry similar to KNbO3 ceramics. Microstructure examined under FEG-SEM revealed an optimum microstructure, in terms of grain size, porosity and uniformity, at the sintering temperature of 1100°C, which also showed density of 92% of ρ Th . As the sintering temperature increased the X-ray diffraction peaks shifted to lower 2θ values indicating excess volatilization of Na at higher temperature as compared to K. This was further confirmed through elemental Probe X-ray microanalysis and ICP–AES studies. Dielectric constant (ε r ), dielectric loss (tanδ), ferroelectric (P–E loop) and piezoelectric (d 33) properties showed considerable improvement and leakage current decreased with increasing sintering temperature. The sample sintered at 1100°C showed marked improvement in maximum dielectric constant (573) at RT at 1kHz, minimum tangent loss (0.04) at RT at 1kHz, maximum remnant polarization (13.5μC/cm2), lower leakage current (7.6×10−7 A/cm2) and maximum d 33 value (100pC/N). [ABSTRACT FROM AUTHOR]

Abstract: The effect of dielectric constant of the PbTiO3 dispersoid on the conductivity of Na2SO4 has been probed. At the Curie temperature, 490 °C, PbTiO3 undergoes ferroelectric to paraelectric phase transition followed by a sharp change in the dielectric constant. The Na2SO4–PbTiO3 composites have been prepared at two different temperatures, namely 600 and 900 °C. Compositions containing 5, 10, 20, 30, 40, 50 m% PbTiO3 have been investigated using Impedance Spectroscopy, Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD) and Rietveld analysis. The series of compositions prepared at 900 °C exhibit a maxima in the conductivity for 20 m% PbTiO3. The composites prepared at 600 °C exhibit a peak in the conductivity at 20 m% PbTiO3 in addition to the percolation threshold at 40 m% PbTiO3. The enhancement in the conductivity by a factor of 40 at 300 °C has been observed for the system prepared at 600 °C while an enhancement in the conductivity by a factor of 8 at 300 °C has been observed for the system prepared at 900 °C. Further, the transition temperature of Na2SO4 remains unaltered for both series. A slight nonlinearity has been observed in the vicinity of the transition temperature of the dispersoid. [Copyright &y& Elsevier]

Abstract: Ferroelectric strontium barium niobate (SBN) powder was synthesized by solid-state route. The green compacts were sintered in the temperature range 1250–1350°C in a microwave furnace. The microstructural study, using SEM, revealed the grain size in the range 2–20μm without microcracks, depending on the sintering temperature. This is in contrast to that obtained conventionally for sintered SBN powder synthesized by solid-state route, which resulted in duplex microstructure with microcracks [N.S. VanDamme, A.E. Sutherland, L. Jones, K. Bridger, S.R. Winzer, J. Am. Ceram. Soc. 74 (1991) 1785; P.K. Patro, A.R. Kulkarni, C.S. Harendranath, Ceram. Int. 30 (2004) 1405; P.K. Patro, Trans. Ind. Inst. Metals 59 (2006) 229]. Impedance analyzer and ferroelectric hysteresis loop tracer were used for the dielectric, ferroelectric, I–V and electric fatigue measurements. Microwave sintering also resulted in a dielectric maxima ε max 2590 at 1kHz (compared to 1103 for conventional sintering [P.K. Patro, A.R. Kulkarni, C.S. Harendranath, Ceram. Int. 30 (2004) 1405]) for the sintering temperature of 1350°C. Similar improvement in microwave-sintered SBN was observed depending on their sintering condition. The origin of this difference is attributed to microstructural differences arising from difference in heating method. In this paper the observed dielectric and ferroelectric behavior have been correlated with different sintering conditions and consequent microstructure due to microwave sintering. [Copyright &y& Elsevier]

Alumina ceramics and Kovar with aluminum interlayer are pressed together under vacuum at temperatures around 600°C for joining. This process produces mechanically strong ceramic to metal bonds in one step in an economic manner. In order to arrive at the optimum conditions for solid-state bonding, effects of bonding temperature, pressure and time on the bond strength have been studied. Bonding kinetics is also elucidated. Irradiation of 99% Al2O3 ceramics by 4-5 MV X-rays has been found to increase the bond-strength sharply from 33 to 60 MPa with a dose of 15 k Rads for bonding temperatures around 540°C. The apparent activation energy for the bonding process (QB) depends strongly on the type of alumina ceramics. Irradiation of alumina ceramics (99%), prior to joining with Kovar, accelerates the solid-state bonding by reducing (QB) from 209 to 76 kJ/mole. [ABSTRACT FROM AUTHOR]

Nano-sized Sr0.5Ba0.5Nb2O6 (SBN50) powder has been synthesized, at very short reaction time, for the first time by a novel combustion method. Ba(NO3)2 and Sr(NO3)2 were used as source of Sr and Ba, respectively, while Nb-oxalate was used as the source of niobium. Urea, hexamethyltetramine (HMT) and glycine were used as fuel. The crystallite sizes in the powder ranged between 14–125 nm. X-ray diffraction analysis showed complete SBN50 phase formation at 700 °C, when urea/HMT was used as fuel, and at 800 °C when glycine was used as fuel. Ferroelectric–paraelectric phase transition temperature (Tc) close to 40 °C was observed when urea and HMT were used and the Tc was −49 °C when glycine was used. When urea was used as fuel highest dielectric constant was observed for the pellets sintered at 1250 °C for 4 h. Low dielectric loss was observed when HMT was used as fuel. Larger grain sizes in the sintered pellets were observed when glycine was used as fuel. [Copyright &y& Elsevier]