• George Varughese

      Articles written in Bulletin of Materials Science

    • Anisotropy in elastic properties of lithium sodium sulphate hexahydrate single crystal—An ultrasonic study

      George Varughese A Santhosh Kumar J Philip Godfrey Louis

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      The double sulfate family (ABSO4), where A and B are alkali metal cations, is the object of great interest owing to the complexity and richness of its sequence of phase transition induced by temperature variation. A new sulfate salt characterized by the presence of water molecule in the unit cell with the chemical formula, Li2Na3(SO4)2.6H2O (LSSW), was obtained. The ultrasonic velocity measurement was done with pulse echo overlap technique [PEO]. All the six second order elastic stiffness constants, 𝐶11 = 𝐶22, 𝐶33, 𝐶44 = 𝐶55, 𝐶12, 𝐶14 and 𝐶13 = 𝐶23 are reported for the first time. The anisotropy in the elastic properties of the crystal are well explained by the pictorial representation of the polar plots of phase velocity, slowness, Young’s modulus and linear compressibility in 𝑎–𝑏 and 𝑎–𝑐 planes.

    • Anisotropy in elastic properties of lithium sodium sulphate hexahydrate single crystal—An ultrasonic study

      George Varughese A S Kumar J Philip Godfrey Louis

      More Details Abstract Fulltext PDF

      The double sulfate family of (ABSO4) where A and B are alkali metal cations, is the object of great interest owing to the complexity and richness of its sequence of phase transition induced by temperature variation. A new sulfate salt characterized by the presence of water molecule in the unit cell with the chemical formula, Li2Na3(SO4)2.6H2O (LSSW), was obtained. The ultrasonic velocity measurement was done with pulse echo overlap technique [PEO]. All the six second order elastic stiffness constants, 𝐶11 = 𝐶22, 𝐶33, 𝐶44 = 𝐶55, 𝐶12, 𝐶14 and 𝐶13 = 𝐶23, are reported for the first time. The anisotropy in the elastic properties of the crystal are well explained by the pictorial representation of the surface plots of phase velocity, slowness, Young’s modulus and linear compressibility in 𝑎–𝑏 and 𝑎–𝑐 planes.

    • Detection of anomalies in NLO sulphamic acid single crystals by ultrasonic and thermal studies

      GEORGE VARUGHESE

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      The ultrasonic pulse echo overlap technique (PEO) has been used to measure the velocities of 10 MHz acoustic waves in sulphamic acid single crystals in the range of 300–400 K. This study evaluated all the elastic stiffnessconstants, compliance constants and Poisson’s ratios of the crystal. The temperature variations of the elastic constants have been determined. The phase transition studies above room temperature were investigated using ultrasonic PEO technique. This study has suggested new weak elastic anomalies for the crystal around 330 K. The transverse elastic constants C44 and C66 have shown clear thermal hysteresis of 2 K. The present differential scanningcalorimetric (DSC) studies carried out at a slow heating rate have also suggested weak phase transition around 331 K. The present elastic and thermal studies have been substantiated by already reported DC electrical conductivitystudies around 330 K.

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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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