Browsing by Author "O.M. Parkash"

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Dielectric and microstructural behaviour of strontium titanate borosilicate glass ceramic system
(Springer India, 1995) O.P. Thakur; Devendra Kumar; O.M. Parkash; Lakshman Pandey
65(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. © 1995 The Indian Academy of Sciences.
Dielectric behaviour of glasses and glass ceramics in the system BaO-PbO-TiO2-B2O3-SiO2
(Springer India, 1987) R.K. Mandal; Ch. Durga Prasad; O.M. Parkash; Devendra Kumar
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. © 1987 Indian Academy of Sciences.
Electrical conduction in the solid solution La1 -x Na x Co1 -x Nb x O3 (0·01 ≤x ≤ 0·99)
(Springer India, 1988) O.M. Parkash; Devendra Kumar; Rabindra Kumar
Seebeck coefficient and DC resistivity of the solid solution La1 -x Na x Co1 -x Nb x O3 (0·01 ≤x ≤ 0·99) have been measured in the temperature range 300-900 K. Seebeck coefficient is positive for all compositions over the temperature range of measurements. Conduction is due to 3 d electrons of cobalt ions in the compositions with x ≤ 0·60. Conduction occurs among localized sites for compositions with x ≥ 0·70. © 1988 Indian Academy of Sciences.
Electron transport and magnetic properties of La1-xSrxCo1-yTiyO3 (x = 0a or x = yb)
(1983) D. Bahadur; O.M. Parkash
The two systems (a) and (b) for different values of x were synthesized. Their electron transport and magnetic properties show a change in behavior above a critical value of x. Unlike the system La1-xSrxCoO3, itinerant electron ferromagnetism is not observed. This is explained on the basis of the absence of an itinerant band of Co4+ whose generation is restricted on account of substitution of Ti4+. Electron transport in these two systems is compared with that of LaCoO3 or La1-xSrxCoO3 and is discussed in view of the presence of different valence states of cobalt and change in crystal field splitting. Spin-state equilibria in these two systems are similar to that in LaCoO3. © 1983.
Equivalent circuit models for electronic ceramics
(Springer India, 1995) Lakshman Pandey; O.M. Parkash; Rajesh K. Katare; Devendra Kumar
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. © 1995 The Indian Academy of Sciences.
Microstructural and dielectric behaviour of glass ceramics in the system PbO-BaO-TiO2-B2O3-SiO2
(Springer India, 1986) O.M. Parkash; Devendra Kumar; R. Rajgopalan
Glasses in the system PbO-BaO-TiO2-B2O3-SiO2 with and without P2O5 as nucleant have been prepared. The glass samples were ceramized based on dta studies. The ferroelectric phase crystallizing out has been found to be BaTiO3 from xrd. The optical and scanning electron micrographs show the presence of BaTiO3 as major phase. In these glass ceramic samples, dielectric constant and dissipation factor are approximately constant with temperature and frequency upto the glass transition temperature T g and thereafter increase sharply with temperature and finally level off. The addition of P2O5 as nucleant and molar ratio of (PbO + BaO) to TiO2 has marked influence on the dielectric behaviour and composition of ferroelectric phase crystallizing out. © 1986 Indian Academy of Sciences.
Preparation and characterization of the system Ba1-xLaxTi1-xCoxO3 (x≤0.50)
(Kluwer Academic Publishers, 1989) O.M. Parkash; Ch. Durga Prasad; Devendra Kumar
[No abstract available]
Preparation structure and dielectric behaviour of the system Sr1-xLaxTi1-xFexO3(x ≤0.50)
(Indian Academy of Sciences, 2003) O.M. Parkash; Devendra Kumar; C.C. Christopher
Formation of solid solution has been explored in the valence compensated perovskite oxide system Sr1-xLaxTi1-xFexO3 (x ≤ 0.50). XRD studies indicate the formation of solid solution for the whole range investigated. All the compositions synthesised have cubic structure similar to undoped SrTiO3. Study of dielectric behaviour of these materials show that orientational polarisation and space charge polarisation contribute significantly to it.