• V Ravi

      Articles written in Bulletin of Materials Science

    • Non-linear 𝐼–𝑉 characteristics of doped Sn1–𝑥Ti𝑥O2 (0.0 < 𝑥 < 0.25) system

      V Ravi S K Date

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      The solid solutions of Sn1–𝑥Ti𝑥O2 (0.0 < 𝑥 < 0.25) were prepared by the usual high temperature ceramic processing techniques with small amounts of dopants such as Nb, Co, Al. The electrical measurements (log 𝐼–log 𝑉) on the ohmically metal electroded sintered pellets showed the non-linear behaviour. The nonlinear coefficient was found to decrease from 12 to 3 with increase in 𝑥. On the other hand, the breakdown voltage (𝐸b) showed the increase with the increase in 𝑥. This complex electrical behaviour is explained on the effects of the three dopants (as varistor former, performance enhancer and highlighter) on the microstructural features of the dense pellet.

    • Preparation of microwave dielectric, Sn0.2Zr0.8TiO4

      Sanjay R Dhage V Ravi S K Date

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      A simple coprecipitation technique is described for the preparation of tin substituted zirconium titanate ceramic powders.

    • Nonlinear 𝐼–𝑉 characteristics study of doped SnO2

      S R Dhage V Ravi S K Date

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      When tin oxide is doped with Sb2O3 and CoO, it shows highly nonlinear current (𝐼)–voltage (𝑉) characteristics. Addition of CoO leads to creation of oxygen vacancies and helps in sintering of SnO2. Antimony oxide acts as a donor and increases the conductivity. The results are nearly the same when antimony oxide is replaced by tantalum oxide. The observed nonlinear coefficient, 𝛼 = 30 and the breakdown voltage is 120 V/mm.

    • Synthesis of nanocrystalline SnO2 powder at 100°C

      Sanjay R Dhage S P Gaikwad Violet Samuel V Ravi

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      A simple gel to crystal conversion route has been followed for the preparation of nanocrystalline SnO2 at 80–100°C under refluxing conditions. Freshly prepared stannic hydroxide gel is allowed to crystallize under refluxing and stirring conditions for 4–6 h. Formation of nano crystallites of SnO2 is confirmed by X-ray diffraction (XRD) study. Transmission electron microscopic (TEM) investigations revealed that the average particle size is 30 nm for these powders.

    • Synthesis of nanocrystalline TiO2 by tartarate gel method

      S R Dhage S P Gaikwad V Ravi

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      A gel was formed when a mixture of TiOCl2 and tartaric acid was heated on a water bath. Ultrafine powders of TiO2 in the anatase phase were formed, when the gel was decomposed at 623 K and the mole ratio of tartaric acid to titanium was 2. The anatase phase was converted into rutile phase on annealing at higher temperatures, > 773 K. When initial ratio of titanium to tartaric acid was < 2, the decomposition of gel leads to the formation of mixed phases of rutile and anatase. However, pure rutile phase was not formed by the decomposition of gel for any ratio of tartaric acid and titanium. These powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and surface area measurements. The average particle size obtained for anatase phase was 3 nm whereas it was 30 nm for rutile phase. Raman scattering experiments were also performed to confirm both anatase and rutile phases.

    • Preparation of nanocrystalline ferroelectric BaNb2O6 by citrate gel method

      S P Gaikwad Violet Samuel Renu Pasricha V Ravi

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      A gel was formed when a aqueous solution of BaCl2, NbF5 and citric acid in stoichiometric ratio is heated on a water bath. This gel on decomposition at 600°C yielded the nano crystallites of BaNb2O6, as confirmed by X-ray diffraction study (XRD). This is a much lower temperature as compared to that prepared by traditional solid state method (1000°C) as reported for the formation of BaNb2O6. Transmission electron microscopic (TEM) investigations revealed that the average particle size is 50 nm for the calcined powders. The room temperature dielectric constant at 1 kHz is found to be 1000. The ferroelectric hysteresis loop parameters of these samples were also studied.

    • A coprecipitation technique to prepare ZnNb2O6 powders

      V V Deshpande M M Patil S C Navale V Ravi

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      A simple coprecipitation technique was successfully applied for the preparation of pure ultrafine single phase, ZnNb2O6 (ZN). Ammonium hydroxide was used to precipitate Zn2+ and Nb5+ cations as hydroxides simultaneously. This precursor on heating at 750°, produced ZN powders. For comparison, ZN powders were also prepared by the traditional solid state method. The phase contents and lattice parameters were studied by the powder X-ray diffraction (XRD). Particle size and morphology were studied by transmission electron spectroscopy (TEM).

    • Preparation of ultrafine LiTaO3 powders by citrate gel method

      S C Navale V Samuel V Ravi

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      A gel was formed when a aqueous solution of Li(NO3), TaF5 and citric acid in stoichiometric ratio was heated in a water bath. This gel on decomposition at 700°C produced fine crystallites of ternary oxide, LiTaO3 (LT). The phase contents and lattice parameters were studied by powder X-ray diffraction (XRD). Particle size and morphology were studied by transmission electron spectroscopy (TEM).

    • Preparation of nanocrystalline Mg4Nb2O9 by citrate gel method

      A Vadivel Murugan A B Gaikwad V Ravi

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      A gel was formed when a aqueous solution of Mg(NO3)2, NbF5 and citric acid in stoichiometric ratio was heated on a water bath. No precipitation was observed at acidic pH and gellation was complete with evaporation of the solvent. This gel on decomposition at 750°C produced nanocrystallites of ternary oxide, Mg4Nb2O9 (M4N2). The phase contents and lattice parameters were studied by powder X-ray diffraction (XRD) at various temperatures. Particle size and morphology were studied by transmission electron spectroscopy (TEM). For comparison, M4N2 powders were also prepared by conventional ceramic route at 900°C.

    • A coprecipitation technique to prepare NaNbO3 and NaTaO3

      V Samuel A B Gaikwad V Ravi

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      A simple coprecipitation technique has been used successfully for the preparation of pure, ultrafine, single phases of NaNbO3 (NN) and NaTaO3 (NT). An alcoholic solution of ammonium carbonate and ammonium hydroxide was used to precipitate Na+ and Nb5+ (or Ta5+) cations under basic conditions as carbonate and hydroxide, respectively. On heating at 700°C, these precursors produce respective products. For comparison, both NN and NT powders were also prepared by the traditional solid state method. The phase purity and lattice parameters were studied by powder X-ray diffraction (XRD). The particle size and morphology were studied by scanning electron microscopy (SEM).

    • A coprecipitation technique to prepare Sr0.5Ba0.5Nb2O6

      A Vadivel Murugan A B Gaikwad V Samuel V Ravi

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      An aqueous mixture of ammonium oxalate and ammonium hydroxide was used to coprecipitate barium and strontium ions as oxalates and niobium ions as hydroxide under basic conditions. This precursor on calcining at 750°C yielded Sr0.5Ba0.5Nb2O6 phase. This is a much lower temperature than that prepared by traditional solid state method (1000°C) as reported for the formation of Sr0.5Ba0.5Nb2O6 (SBN). Transmission electron microscopic (TEM) investigations revealed that the average particle size was 80 nm for the calcined powders. The room temperature dielectric constant at 1 kHz was found to be 1100. The ferroelectric hysteresis loop parameters of these samples were also studied.

    • Low voltage varistor ceramics based on SnO2

      S R Dhage V Ravi O B Yang

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      The nonlinear current (𝐼)–voltage (𝑉) characteristics of tin dioxide doped with either Nb2O5 and CoO or Sb2O3 and CoO show promising values of nonlinear coefficient (𝛼) values (∼11) with low breakdown voltages (𝐸B, ∼40 V mm-1). The pentavalent antimony or niobium acts as donor and increases the electronic conductivity. The crucial parameter for obtaining low breakdown voltage is the grain size, which depends upon sintering duration and temperature of these oxide ceramics.

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