• V R Palkar

      Articles written in Bulletin of Materials Science

    • Fine particle physics and technology; some results

      M S Multani N G Nanadikar V R Palkar A K Pansare A Gurjar R Vijayaraghavan

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      The new techniques of fine particle synthesis are shown to lead to better ceramic materials such as yttrium iron garnet (YIG) and ferroelectric lead zirconate titanate (PZT). The densities are greater than 99% of the theoretical density and the grain size can be easily controlled from 2 microns upwards. For YIG this means higher values of the nonlinear spin-wave excitation thresholdhc. For PZT the result is higher values of the tensor componentd33 and poling voltage. It is also shown that the fine particle systems and the fine-grain microstructure lead to interesting physics results. For PZT the lowering of the peak dielectric constant, the increasing transition temperatures and the decreasing values ofd33 with decreasing grain size can be understood in terms of the changing low-frequency cut-off of the soft lattice vibration mode. Another interesting result is that for 2000 Å size particles of α-Fe2O3 the anisotropy constant is found to be 1·38 × 102 ergs/cm3 from Mössbauer measurements.

    • Microcrystals of cooperative-behaviour materials

      M S Multani R Vijayaraghavan M R Srinivasan P Ayyub V R Palkar V Saraswati A V Gurjar

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      Properties of materials exhibiting cooperative phenomena are likely to be modified on restricting the lattice size. Several such microcrystalline materials have been studied to infer general underlying principles. Ferroelectricity, ferromagnetism, superconductivity, and superfluidity in limited lattice sometimes not only show modified behaviour but also new behaviour not present in bulk. Microcrystals are considered to be free, coupled, grain-boundary-separated, or domain-wall-separated.

    • Amorphous state ferroelectricity, magnon scattering and phase stability in microparticle materials

      M S Multani P Ayyub V R Palkar M R Srinivasan V Saraswati R Vijayaraghavan DO Shah

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      Microparticles and micrograin ceramics show features distinct from the usual-sized polycrystalline materials. Amorphous state material combined with microparticle size for Pb(Zr0.51 Ti0.49)O3 mimics the dielectric behaviour of crystalline ferroelectricity in ABO3 compounds. Fine-grained Y3Fe5O12 (yig) synthesized by pressure sintering ofyig microparticles exhibit spinwave relaxation due to transit time across grain diameter. Applying microemulsion techniques for microparticle synthesis,γ-Fe2O3 has been synthesized. The phase stability fractionγ-Fe2O3/α-Fe2O3 is found to be a function of particle size. At very small sizesγ-Fe2O3 becomes amorphous, leading to interesting Mössbauer studies.

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    • Dr Shanti Swarup Bhatnagar for Science and Technology

      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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