Lakshman Pandey

Crystallization, microstructure development and dielectric behaviour of glass ceramics in the system [SrO · TiO2]-[2SiO2 · B2O3]-La2O3

Various glasses in the system (65 − x)[SrO · TiO2]-(35)[2SiO2 · B22O3]-(x)La2O3, where x = 1,5,10 (wt%) were prepared by melting in alumina crucible (1375–1575 K). Heat treatment schedules were selected from DTA plots of respective glasses. X-ray diffraction studies of glass ceramic samples containing different concentrations of La2O3 revealed the formation of Sr2B2O5, Sr3Ti2O7 and TiO2 (rutile) phases. The addition of La2O3 results in the development of well formed, elongated crystallites of different phases. Results of the dielectric behaviour demonstrate higher values of dielectric constant for some of the glass ceramic samples. This can be ascribed to the relaxation polarization at the crystal-glass interface due to conductivity differences between crystalline and glassy phases.

Equivalent circuit models for electronic ceramics

Complex immittance spectra of model equivalent circuits involving resistive and capacitive elements are calculated. A comparison of experimentally obtained complex immittance plots with these diagrams greatly facilitates the search for the most appropriate equivalent circuit representing the electrical properties of electronic ceramics.

Effect of K2O addition on crystallization and microstructural behaviour of the strontium titanate-borosilicate glass-ceramic system

Abstract The crystallization and microstructural behaviour of glass ceramics in the system (SrO · TiO 2 )-(SiO 2 · B 2 O 3 ) with varying wt% of K 2 O have been investigated. The glass samples were crystallized based on DTA studies. Crystalline phases were identified by X-ray diffraction. The addition of K 2 O in the parent glass composition plays an important role in the precipitation of different crystalline phases in glassy matrix and controls the microstructure of the resulting glass ceramic. In our studies it has been observed that careful selection of the K 2 O content and heat-treatment conditions results in crystallization of strontium titanate as the major phase.

Dielectric and microstructural behaviour of strontium titanate borosilicate glass ceramic system

Abstract65(SrO·TiO2)−35(2SiO2·B2O3) wt% glass was synthesized. Differential thermal analysis study shows one exothermic peak which shifts towards higher temperature with increasing heating rate. Glass ceramics prepared by controlled crystallization of strontium titanate borosilicate glass produce uniform distribution of crystallites in a glassy matrix. Attempt was made to crystallize strontium titanate phase in this glass ceramic. Different phases precipitated out during ceramization have been identified by X-ray diffraction. It appears that due to high reactivity of SrO with B2O3, strontium borate crystallizes as principal phase followed by TiO2 (rutile) and Sr3Ti2O7 phases. Dielectric constant of these glass ceramics was observed to be more or less temperature independent over wide range of temperatures with low values of dielectric constant and dissipation factor.

Diffuse phase transition in (Ba, Ca) TiO3 ceramics

Abstract Dielectric behaviour of (Ba, Ca) TiO3 ceramics prepared by conventional and a novel technique has been studied as function of temperature and frequency. It is shown that by ensuring uniform distribution of Ca2+ ions in the BaTiO3 matrix, the transition from the ferroelectric to the paraelectric phase becomes more diffuse and is free from any relaxational effects at least up to 10 KHz. It is suggested that the relaxor behaviour of ceramics exhibiting diffuse phase transitions is due to the limitations of the processing techniques and is not the intrinsic property of the material.

Crystallization and microstructural behaviour of strontium titanate borosilicate glass ceramics with Bi2O3 addition

Glasses in the system (65 −x) [SrO·TiO2] − (35) [2SiO2·B2O3] − (x) [Bi2O3] wherex = 1, 5, 10 (wt%) prepared by melting in alumina crucible (1375–1575 K), were subjected to different heat treatment schedules followed by DTA studies. Crystallization study showed the formation of Sr2B2O5 as major phase at low temperature (≈950°C) heat treatment. At high temperatures, TiO2 and SrTiO3 with or without Sr2B2O5 crystallize out depending on heat treatment. In this paper, the influence of variation in composition, thermal treatment on the nature of crystallizing phases as well as on the resulting microstructures are investigated through XRD, IR and SEM. Uniform crystallization was achieved by suitable addition of Bi2O3 and proper heat treatment.

Glass ceramics containing ferroelectric phases

Glass ceramics prepared by controlled crystallization of glasses produce fine dispersion of crystallites in a glassy matrix. Glasses containing a mjor portion of constituents of a ferroelectric phase produce crystallites of ferroelectric phase in glass through a suitable heat treatment. The amount of network former in the initial glass has a profound influence on its crystallization behaviour and microstructure of the resulting ferroelectric glass ceramics. The value of dielectric constant and the nature of ferroelectric to paraelectric transition depend on the crystallite size and volume fraction of the ferroelectric phase. These glass ceramics are transparent for crystallite size less than 0·1µm and exhibit large quadratic-electro-optic effect.

Evidence of two ferroelectric PTCR components in valence-compensated ceramic system Ba1-xLaxTi1-xCoxO3

The electrical behaviour of valence-compensated ceramic system Ba1−xLaxTi1−xCoxO3 has been studied as a function of temperature (300–600 K) and composition (x ⩽ 0·20), using the method of impedance spectroscopy. The necessary equivalent circuit models that represent the data best have been obtained using impedance and modulus formalisms and grain and grain boundary contributions have been separated out. The compositionsx = 0·20 and 0·10 show a negative temperature coefficient of resistance (NTCR) behaviour whereas a very small variation of the grain and grain boundary resistance with temperature is observed forx = 0·05. A positive temperature coefficient of resistance (PTCR) behaviour having two ferroelectric components is observed forx = 0·01. These results reveal limitations in current theories of the PTCR effect.

Preparation, structure and dielectric properties of the system Sr1−xLaxTi1−xNixO3

Attempts have been made to synthesize the solid solution Sr1−xLaxTi1−xNixO3 for x⩽0.50 and its electrical behaviour has been studied. It was found that a solid solution forms for compositions up to x=0.10. The structure remained cubic. These compositions exhibited dielectric relaxator behaviour. The average grain size in these materials was very small.

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.