• Volume 1, Issue 2

      October 1979,   pages  79-128

    • Alpha-Quartz 2. Crystal chemistry, and nature and distribution of impurities

      Prasenjit Saha Tarun Bandyopadhyay

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      Crystal chemistry of alpha-quartz is discussed in relation to the nature, concentration and distribution of the common impurities. Two schemes for incorporation of impurities in the host structure,viz., the charge compensation model for untwinned natural quartz, and the broken-bond model for synthetic quartz to accomodate excess impurity residue after charge compensation, are critically reviewed. Another model for the presence of Al-H defects independent of alkali association in natural quartz is suggested. It is pointed out that the growth pressure influences the nature and distribution of impurities as well as generation of planar and line defects in synthetic quartz. It is also established that mechanicalQ (which is a measure of the acoustic loss) of synthetic crystals grown at low pressure deteriorates with increase in impurity content in excess of what is required for satisfying the charge compensation rule.

    • Research in magnetism at Indian institute of technology, Bombay

      C M Srivastava

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      The experimental solid state physics group at the Indian Institute of Technology, Bombay, has been engaged in research on ferromagnetic resonance and relaxation, magnetic ordering and exchange phenomena in ferrimagnetic systems. A brief report on the facilities developed and the work done by the magnetism group is presented.

    • Kinetics of the oxidation of CuFeO2 in Cu-Fe-O system

      G C Jain B K Das R Avtar

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      The oxidation kinetics of CuFeO2 in Cu-Fe-O system have been studied between temperature range 500° C and 900° C in an ambient atmosphere containing constant oxygen partial pressure in the flowing nitrogen. Thermogravimetric analysis (TGA) technique was used as the main tool. The oxidation rate was found to decrease and the activation energy calculated from the oxidation rate constants for various composition increased from 8 to 45 k cal/mole on increasing the Fe2O3 content in the system. The value of exponentn in Avrami’s equation=1 − exp (−ktn) also increased from 1·3 to 2·3. The microstructural changes associated with the oxidation have been studied using optical microscopy and correlated with results obtained from thermogravimetric analysis.

    • Growth and characterisation of TaS2 single crystals

      M K Agarwal J V Patel H B Patel

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      Single crystals of tantalum disulphide have been grown by a sublimation or direct vapour transport method. Crystals as large as 15×10×0·05 mm3 grew in the form of platelets and needles above the charge which was kept well distributed within the ampoule. Characterisation of the as-grown crystals has been carried out at room temperature by x-ray diffraction. Electrical conductivity and magnetic susceptibility measurements have also been made.

    • Itinerant electron behaviour and long-range ordering in La1−xSrxCoO3

      P Ganguly W H Madhusudan

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      Electrical resistivity of La1−xSrxCoO3 is reduced significantly by the substitution of Ni3+ ions in place of the cobalt ions. In the La1−xSrxCo1−yNiyO3 system, for small values ofx(x=0·05) superparamagnetic clusters seem to be formed at lower temperatures (<300 K). The formation of such clusters is not affected by the presence of nickel ions. Whenx is large, the occurrence of long-range ordering seems to depend on the itinerancy of charge carriers.

    • Measurement of magnetic properties of single crystal YIG by non-resonant method

      D N Bose S R Borgaonkar T S Vedavathy

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      A non-resonant microwave technique has been employed for the determination of saturation magnetisation (4πMs) andg-factor of pure and Gd-doped single crystal YIG spheres yielding accurate values. It was found that 4πMs=1720–1751 g for undoped and 1595 g for 10% Gd-doped YIG spheres whilegeff=2·00–2·0039. The advantages of this method are simplicity and complete absence of propagation corrections necessary in cavity resonance experiments.

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