• Lakshman Pandey

      Articles written in Bulletin of Materials Science

    • Glass ceramics containing ferroelectric phases

      Om Parkash Devendra Kumar Lakshman Pandey

      More Details Abstract Fulltext PDF

      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.

    • Equivalent circuit models for electronic ceramics

      Lakshman Pandey O M Parkash Rajesh K Katare Devendra Kumar

      More Details Abstract Fulltext PDF

      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

      More Details Abstract Fulltext PDF

      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

      More Details Abstract Fulltext PDF

      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.

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

      O P Thakur Devendra Kumar Om Parkash Lakshman Pandey

      More Details Abstract Fulltext PDF

      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.

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

      Lakshman Pandey Rajesh K Katare Om Parkash Devendra Kumar

      More Details Abstract Fulltext PDF

      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.

  • Bulletin of Materials Science | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.