• Vishnu Shanker

      Articles written in Bulletin of Materials Science

    • Comparative study of dielectric properties of MgNb2O6 prepared by molten salt and ceramic method

      Vishnu Shanker Ashok K Ganguli

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      Magnesium niobate (MgNb2O6) powder was synthesized by the conventional ceramic route as well as by the molten salt route using a eutectic mixture of NaCl–KCl as the salt and Mg(NO3)$_2\cdot$6H2O and TiO2 as the starting materials. Pure phase of MgNb2O6 could be obtained by the molten salt method at 1100°C. However, in ceramic method the pure phase of MgNb2O6 was obtained by heating at 1025°C for 20 h. On sintering at 1100°C the dielectric constant and dielectric loss of MgNb2O6 obtained by the molten salt method was found to be 19.5 and 0.004 at 100 kHz at room temperature. Lower values were obtained for these oxides prepared by the ceramic route, 16.6 and 0.000518, respectively. In both cases the dielectric constant was quite stable with frequency.

    • Investigation of Ba2–𝑥Sr𝑥TiO4: Structural aspects and dielectric properties

      Vishnu Shanker Tokeer Ahmad Ashok K Ganguli

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      Investigation of solid solution of barium–strontium orthotitanates of the type, Ba2–𝑥Sr𝑥TiO4 (0 ≤ 𝑥 ≤ 2), show that pure phases exist only for the end members, Ba2TiO4 and Sr2TiO4, crystallizing in the 𝛽-K2SO4 and K2NiF4 structures, respectively. The intermediate compositions (till 𝑥 ≤ 1) lead to a biphasic mixture of two Ba2TiO4-type phases (probably through a spinodal decomposition) with decreasing lattice parameters, indicating Sr-substitution in both the phases. For 𝑥 > 1, Sr2TiO4 along with a secondary phase is obtained. The dielectric constant and dielectric loss were found to decrease with Sr substitution till the nominal composition of 𝑥 = 1. However, pure Sr2TiO4 shows higher dielectric constant compared to the solid solution composition. Sr2TiO4 shows very high temperature stability of the dielectric constant.

    • Dielectric behaviour of sodium and potassium doped magnesium titanate

      Vishnu Shanker Santosh Kumar T Surendar

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      Pure phase of magnesium titanate (MgTiO3) was obtained at 1100°C by both the conventional solid-state method as well as by the flux method starting from hexahydrated magnesium nitrate and titanium dioxide as the reactants. MgTiO3 doped with Na or K was also prepared by the solid-state route. Na and K doped compositions led to monophasic MgTiO3 below 5 mol% dopant concentration while biphasic mixture of MgTiO3 (major phase) and MgTi2O5 (minor phase) were obtained at higher dopant concentration. The dielectric constant and dielectric loss of MgTiO3 were found to be almost the same irrespective of the preparative method. MgTiO3 doped with 5 mol % of Na and K ions displayed optimum dielectric properties.

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