• Volume 2, Issue 2

      May 1980,   pages  83-150

    • Characterisation of bubble materials

      M J Patni Om Parkash D Bahadur

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      The rapid development of magnetic bubble technology has required growth to exacting specifications of a large number of magnetic films of garnets and some amorphous binary and ternary alloys of rare-earth and transition metals. The characterisation of these films is an essential part in the search for newer materials which hold out promise for better device performance and cost viability. Many methods of films characterisation have been reported from time to time. By and large, these methods can be divided into two groups: one, bulk measurements made on the film and two, measurements made on the domains. We have attempted to collate and briefly introduce various techniques to characterise magnetic bubble materials in this review.

    • Alpha-quartz 3. Origin of cellular structure of synthetic quartz

      Prasenjit Saha Tarun Bandyopadhyay

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      Surfaces of optically flawless and untwinned quartz single crystals, both natural and synthetic, were dissolved both at room temperature and at high temperatures in autoclaves using appropriate etchants. The features that develop have been optically studied, and x-ray transmission projection topographs of some of the specimens from the same natural quartz were also taken and studied. A model has been proposed to explain the anomalies detected earlier by other workers regarding the nature of line defects found in as-grown synthetic quartz, and the absence of lateral strain in the polygonised microcracked layer of the specimens of the present series of experiments.

    • Dual anvil high pressure cell

      A K Bandyopadhyay B S Sivaram S V Subramanyam

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      A dual level high pressure cell using Bridgman anvils was constructed to facilitate simultaneous measurement on the samples. The anvils were of 4 mm and 5 mm diameter respectively. The anvils were made from tungsten carbide (3% cobalt binder). Pyrophyllite and steatite were used as the gasket and the pressure transmitting medium. The cell was calibrated against the polymorphic phase transition of bismuth and ytterbium.

    • Growth of single crystals of some complex salts in silica gels

      M S Joshi P Mohan Rao A V Antony

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      Single crystals of ammonium nickel sulphate, potassium nickel sulphate, ammonium alum and potassium alum are grown in sodium-metasilicate gels. The method of gel preparation and growth procedure are described. Both single diffusion and double diffusion methods are used. Studies on nucleation and characterisation of crystals are also reported. Crystals grown are illustrated.

    • CuAlMnO4 from two different combinations and their structural and electrical study

      A B Devale H S Bisht D K Kulkarni

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      A compound CuAlMnO4 has been synthesised for the first time by oxide method using 1+ and 2+ copper oxides separately. Both the compounds crystallise in tetragonal unit cell witha=8·205 A andc=8·342 A. It has been observed that there are similarities in structures but dissimilarities in their electrical behaviours. The observed tetragonal symmetry, lattice dimensions and electrical behaviour are explained on the basis of solid solution of CuAl2O4 and CuMn2O4 spinels.

    • Evidence of edge and screw dislocations in gypsum single crystals

      K S Raju

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      A row of closely packed equispaced etch pits are observed on etching (010) basal cleavages of gypsum with analar grade nitric acid and 0·1 N potassium hydroxide solution. It is established that these rows of pits are true to the whole bulk of the crystal, by successive etching and etching of match pairs, thin flakes as well as using different etchants. These rows of pits reveal low angle grain boundaries consisting of equispaced edge dislocations in the crystal. Irregular arrays of etch pits observed exactly correspond to its match face. Studying these rows on higher resolution, it is observed that they may reveal tilt or twist boundaries consisting of both edge and screw dislocations, probably created due to the impingement of the mis-oriented guest crystal causing stresses to the growing crystal. The implications are discussed.

    • Studies of defects in WSe2 single crystals

      M K Agarwal H B Patel T C Patel

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      A realistic estimation of growth and deformation fault probability has been made in the crystals of WSe2 grown by a direct vapour transport method. Electron microscopy of the specimens revealed the presence of two-fold ribbons from which theγ/μ ratio has been determined. Attempts to study polytypism have also been described.

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