• O M Parkash

      Articles written in Bulletin of Materials Science

    • LaNi1−xCoxO3 as interconnection materials

      O M Parkash

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      Thermo Gravimetric Analyis (TGA) shows that incorporation of Co3+ considerably reduces the oxygen loss at high temperatures in LaNiO3. Electrical resistivity of LaNi1−xCoxO3 (x⩽0·2) is essentially independent of oxygen partial pressure in the 600–1000 K range.

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

      R K Mandal Ch Durga Prasad O M Parkash Devendra Kumar

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      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.

    • Electrical conduction in the solid solution La1 −xNaxCo1 −xNbxO3 (0·01 ⩽x ⩽ 0·99)

      O M Parkash Devendra Kumar Rabindra Kumar

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      Seebeck coefficient and DC resistivity of the solid solution La1 −x NaxCo1 −xNbxO3 (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 3d electrons of cobalt ions in the compositions withx ⩽ 0·60. Conduction occurs among localized sites for compositions withx ⩾ 0·70.

    • Preparation and characterization of Ca1 −xLaxTi1 −xCoxO3 (0·00<x⩽0·50) system

      O M Parkash Ch Durga Prasad Devendra Kumar

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      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.

    • Equivalent circuit models for electronic ceramics

      Lakshman Pandey O M Parkash Rajesh K Katare Devendra Kumar

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      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.

    • Dielectric and microstructural behaviour of strontium titanate borosilicate glass ceramic system

      O P Thakur Devendra Kumar O M Parkash Lakshman Pandey

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      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.

    • Effect of 1 wt% CoO addition on dielectric and microstructural behaviour of (SrO·TiO2)-(2SiO2·B2O3) glass and glass ceramic

      O P Thakur Devendra Kumar O M Parkash Lakshman Pandey

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      Glass of the nominal composition 64 wt%(SrO·TiO2)·35 wt%(2SiO2·B2O3)-1 wt%(CoO) was prepared. The glass samples were subjected to heat treatment at 900 and 950 C. The phase progression in these glass ceramics from X-ray diffraction studies shows the formation of Sr2B2O5 as primary crystalline phase followed by rutile (TiO2), Sr3Ti2O7, SrB2Si2O8 and Sr3B2SiO8 as secondary phases. The first DTA exothermic peak of glass corresponds to the crystallization of Sr2B2O5, rutile and Sr3Ti2O7 phase while second crystallization peak may be assigned to the formation of SrB2Si2O8 and Sr3B2SiO8 phases. From microstructure studies we find that strontium borate grows with larger grain size whereas the other phases like Sr3Ti2O7, TiO2 appear smaller in size. Cobalt oxide content in the strontium titanate borosilicate glass ceramic gives the thermal stability to dielectric behaviour and decreases the dielectric loss.

    • Effect of composition on dielectric and electrical properties of the Sr1 −xLaxTi1 −xCoxO3 system

      Shail Upadhyay Devendra Kumar O M Parkash

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      Valence compensated perovskite system Sr1 −xLaxTi1 −xCoxO3 shows dielectric relaxor behaviour with very high value of dielectric constant in the composition range 0·20 <x < 0·40. In this paper the effect of composition on microstructure and the resulting electrical behaviour is reported. The compositions withx = 0·25, 0·30, 0·33, 0·35 and 0·37 have been synthesized by solid state ceramic method and dielectric measurements were made in the temperature range of 300–500 K and frequency range of 100 Hz to 1 MHz. Grain boundaries played an important role in their dielectric behaviour. Complex plane impedance and modulus techniques were used to separate out the contributions of grain and grain-boundaries to the resulting dielectric behaviour. It was observed that the bulk resistivity as well as the grain boundaries resistance decreased with increasingx. Furthermore, impedance analysis demonstrated that extremely high value of dielectric constant observed in these materials was due to barrier layers formation at grain-grain-boundaries interfaces.

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