V. B. Tare

Thermodynamic stability of barium zirconates

The standard free energy of formation of BaO·ZrO2 prepared by solid state reaction at elevated temperatures was determined in the temperature range 937 K to 1150 K using barium fluoride as solid electrolyte and barium hexa ferrite as the reference electrode. The data obtained are represented by the equation ΔGBaO·ZrO2 = −105164 + 49.37T (±340J) where ΔGBaO·ZrO2 is the free energy of formation of BaO·ZrO2 from BaO and ZrO2.

Study of the electrical conduction behaviour of the Ba1−xLaxTi1−xNixO3 (x ⩽ 0.10) system

Abstract The electrical conduction behaviour of the Ba 1− x La x Ti 1− x Ni x O 3 ( x ⩽ 0.10) system has been studied by complex plane impedance analysis and measurements of a.c. conductivity in the temperature range 400–575 K. The values of the bulk resistance for these samples are obtained from a circular arc passing through the origin in their impedance plots. A.c. conductivity obeys the relation σ a.c. αω 8 in the temperature range of measurements. These results indicate that conduction occurs in this system because of hopping of charge carriers between localized nickel sites.

Free energy of formation of barium ferrites

The free energy of formation (AG°) of various ferrites in the system BaO-Fe2O3 was determined with galvanic cells using barium fluoride as solid electrolyte. The values of ΔG° per mole of 2 BaO · Fe2O3, BaO · Fe2O3 and BaO · 6 Fe2O3 from BaO and Fe2O3 were found to be-10,953 (±2275) J, -68,496 (±435) J, -75,576 (±250) J at 1200 K and-104,600 (±2275) J, -66,875 (±435) J, -74,437 (±250) J at 1300 K respectively.

Dielectric relaxator behaviour of Sr0.8La0.2Ti0.8Co0.2O3

Abstract Sr1−x La x Ti1−x Co x O3 for x ≤ 0.4 exhibits dielectric relaxator behaviour. The effect of firing temperature and different electroding on the dielectric properties of the sample Sr0.8La0.2Ti0.8Co0.2O3 has been investigated. Higher firing temperatures have no effect on the microstructure and on the resulting dielectric properties. On electroding with silver paint containing a low melting glass, CuO and Bi2O3 and heat-treating at 900 K for 15 minutes, the dielectric constant increased and the dielectric loss decreased. The dielectric characteristics have been analysed using complex plane impedance analysis.

Dielectric properties of the system Ca1−xYxTi1−xCoxO3(0.00 ⩽ x ⩽ 0.15)

The dielectric behaviour of the compositions withx⩽0.15 in the system Ca1−xYxTi1−xCoxO3 sintered and cooled in air has been studied. Space-charge polarization which arises due to the presence of chemical inhomogeneities at the micro-level contributes significantly to their dielectric constant. The composition with x=0.05 exhibits temperature and frequency-independent dielectric constant and very small dielectric loss.

Electrical conduction in calcium yttrium titanium cobalt oxide Ca1-xYxTi1-xCoxO3 (x<or=0.15)

The DC resistivity and Seebeck coefficient have been measured as a function of temperature in the system Ca1-xYxTi1-xCoxO3 for the samples with x<or=0.15 in the range 300-800 K. AC conductivity has been measured as a function of temperature and frequency. Results of these measurements show that electrical transport occurs mainly by a Debye-type loss process at temperatures less than 375 K and by excitation of charge carriers at localized states close to band edges and hopping among the localized sites.

Influence of aluminum and chromium on the activity of oxygen in nickel based melts at 1600‡C

The activity of oxygen in technically important nickel melts containing 15 wt pct cobalt and 5 wt pct molybdenum has been determined at 1600‡C for various concentrations of chromium ranging from 0 to 30 wt pct and aluminum varying from 0 to 15 wt pct. The activity of oxygen was measured by an electrochemical technique using yttria-doped thoria electrolyte cells. The results obtained are analyzed in terms of activity coefficients of oxygen as a function of aluminum and chromium contents in the melts. Clear positive deviations of the experimentally determined from the calculated activity coefficients of oxygen were found when aluminum was added to Ni-Co-Mo melts with or without chromium. From the results obtained in the range between 1 and 10 wt pct aluminum, the following equilibrium constants for the reaction 2 [Al] + 3 [O] ⇋ Al2O3 in the nickel based melts at 1600‡C were calculated: loga0 =-2/3 log [pct Al] - 3.94 for 0 pct Cr loga0 = -2/3 log [pct Al] - 4.21 for 10 pct Cr loga0 = -2/3 log [pct Al] - 4.81 for 20 pct Cr loga0 = -2/3 log [pct Al] - 5.06 for 30 pct Cr.

Thermodynamic properties of barium chromate

Abstract The standard free energy of formation of BaCrO 4 was determined in the temperature range 935 to 1187 K using barium fluoride as solid electrolyte and barium hexaferrite as reference electrode. The data obtained are represented by the equation Δ G BaCrO 4 = −3.17T−81008(±340J) where ΔG BaCrO 4 is the free energy of formation of BaCrO 4 from BaO and Cr 2 O 3 .