Ch. Durga Prasad

Low-temperature synthesis of chemically homogeneous lead zirconate titanate (PZT) powders by a semi-wet method

A semi-wet procedure for the synthesis of single-phase Pb(ZrxTi1−x)O3 powders at 600 °C is described. The ultrafine powders so obtained do not exhibit tetragonal/rhombohedral distortions until they are sintered at higher temperatures. The morphotropic phase boundary (MPB) for these powders, which are chemically homogeneous, lies between x=0.52 and 0.53. For x=0.525, the rhombohedral and tetragonal phases coexist.

Dielectric relaxator behaviour of the system Sr1−xLaxTi1−xCoxO3 (x ⩽ 0.40)

The dielectric behaviour of the valence-compensated solid solution Sr1−xLaxTi1−xCoxO3 (x=0.05, 0.10, 0.20, 0.30 and 0.40) has been studied as a function of temperature and frequency. Compositions withx=0.20, 0.30 and 0.40 exhibit high values of dielectric constant. This high dielectric constant is due partly to the presence of interfacial polarization, and partly to the formation of grain-boundary barrier layers in these materials. The presence of barrier layers is shown by complex plane impedance analysis.

Dielectric behaviour of glasses and glass ceramics in the system BaO-PbO-TiO2-B2O3-SiO2

Glasses with varying molar ratios of PbO/BaO in the system BaO-PbO-TiO2-B2O3-SiO2 were prepared keeping (BaO + PbO)/TiO2 ratio equal to one. The glasses were ceramized by two-stage heat treatment. X-ray diffraction indicates that PbTiO3 crystallizes in lead-rich glasses while BaTiO3 precipitates in barium-rich compositions. Solid solution (Ba, Pb)TiO3 does not seem to crystallize over the entire range of compositions. Simultaneous presence of PbO and BaO in the initial glass composition reduces the yield of ferroelectric phase. Dielectric properties have been interpreted in terms of microstructural features.

Preparation and characterization of lanthanum lead cobalt titanium oxide, La1−xPbxCo1−xTixO3 (0 < x < 1)

Attempts have been made to prepare the solid-solution La/sub 1-x/Pb/sub x/Co/sub 1-x/O/sub 3/ for 0 < x < 1. X-ray diffraction indicates the formation of single-phase materials over the entire range. Compositions with 0 < x less than or equal to 0.20 are rhombohedral, those with x in the range 0.2 to 0.8 are cubic, and those with x greater than or equal to 0.9 are tetragonal. Chemical analysis shows that all these samples are lead deficient. This is due to volatilization of PbO during preparation. Conduction is mainly due to 3d electrons of cobalt ions. All the samples except x = 0.05 show p-type conduction at and above 300 K. Samples with x greater than or equal to 0.5 exhibit dielectric anomaly at a particular temperature which increases the increasing x.

Electrical conductivity behaviour of the solid solution Ba1−xLaxTi1−xCoxO3

Abstract The d.c. resistivity and Seebeck coefficient were measured as a function of temperature in the Ba 1− x La x Ti 1− x Co x O 3 system for samples with x ⩽ 0.50 in the 300–800 K temperature range. The a.c. conductivity was measured as a function of temperature and frequency for samples with x ⩽ 0.20. The a.c. conductivity data indicate that conduction occurs among localized sites giving rise to Debye-type loss at low temperatures. The results of d.c. conductivity measurements combined with a.c. conductivity data at high temperatures indicate that electrical transport occurs by the excitation of charge carriers near the valence band edge and hopping as small polarons at energies close to it.

Electrical properties of the system lanthanum lead cobalt titanium oxide

Measurements of DC electrical resistivity and Seebeck coefficient on the perovskite system La1−xPbx−δ Co1−xTixO3−δ for 0·2≤x≤0·9 have been made in the temperature range 300–800 K. AC conductivity,σa.c, of all the samples were measured as a function of temperature (300–573 K) and frequency (1 kHz-1 MHz). DC resistivity behaviour of all the samples is similar. However, the resistivity value, which varies over 5–6 orders of magnitude, depends on both the compositionx and the structure of the samples. All the samples exhibitp-type electronic conduction. The value of Seebeck coefficient,α, for samples withx≤0·5 initially increases with temperature up to a particular temperature. Above this temperature, the behaviour ofα for samples withx≤0·5 and for samples withx>0·5 over the entire temperature range is similar to that of La CoO3. All the samples exhibit frequency-dependent a.c. conductivity at low temperatures.

Electrical conduction in the Sr1-xLaxTi1-xCoxO3 (x<0.40) system

Direct current resistivity and the Seebeck coefficient ( alpha ) have been measured in the temperature range 300-800 K for compositions x<or=0.40 in the Sr1-xLaxTi1-xCoxO3 system. Alternating current conductivity has been measured as a function of frequency and temperature. Positive values of alpha over the entire range of measurement show that holes are the majority charge carriers. Alternating current conductivity shows that conduction occurs due to hopping of charge carriers among localized sites.

Preparation and characterization of Ca1 −x La x Ti1 −x Co x O3 (0·00<x⩽0·50) system

The possibility of the formation of solid solution in the system Ca1 −xLaxTi1 −x CoxO3 forx⩽0·5 has been investigated. X-ray diffraction studies show that compositions withx=0·05, 0·1, 0·2, 0·3 and 0·5 prepared by the ceramic method are single-phase materials. All the compositions have a structure similar to CaTiO3 with a pseudo-cubic unit cell. Preliminary studies show that interfacial polarization contributes significantly to their dielectric constant.

Electrical conduction in calcium lanthanum titanium cobalt oxide, Ca1−xLaxTi1−xCoxO3 (x≤0.50)

The DC resistivity and the Seebeck coefficient have been measured as a function of temperature in the system Ca1-xLaxTi1-xCoxO3 for the samples with x<or=0.50 in the range 300-800 K. AC conductivity has been measured as a function of temperature and frequency for the samples with x<or=0.20 AC conductivity data indicate that conduction occurs due to hopping of charge carriers among localised sites giving rise to a Debye-type loss process at low temperatures. Results of AC resistivity combined with DC resistivity show that at high temperatures electrical transport occurs by excitation of charge carriers at the valance band edge and hopping at energies close to it.

Dielectric properties of the system Ca1 −x La x Ti1 −x Co x O3

Dielectric behaviour of samples of the system Ca1 −xLaxTi1 −xCoxO3 withx ⩽ 0·20 has been studied in the temperature range 300–525 K as a function of frequency. The strong dispersion ofɛ andD observed in these materials indicate the significant contribution of interfacial polarisation to the observed dielectric properties. The interfacial polarisation arises due to the presence of microscopic chemical heterogeneities arising out of the slow diffusion-controlled solid state sintering process used for their preparation.