• S Usha Devi

      Articles written in Bulletin of Materials Science

    • The pressure-volume relation of ytterbium up to 9 GPa

      S Usha Devi A K Singh

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      The pressure-volume relation of ytterbium has been determined up to 9 Gpa using tungsten carbide opposed anvil high pressure x-ray camera. The fcc phase of ytterbium is observed between one atmosphere and 4 GPa and the bcc phase above 3·5 GPa. The bcc phase can be metastably retained down to 1 GPa by gradually decreasing the pressure from a region where only bcc phase alone is observed. The bulk modulus,B0, at zero pressure and the pressure derivative of the bulk modulus,B’0, are determined by fitting Murnaghan equation to the pressure-volume data. The following values were obtained:B0=16·3 GPa andB’0=3·6 for the fcc phase, andB0=14·7 GPa andB’0=1·5 for the bcc phase. Based on the present data it is suggested that the thermodynamic equilibrium pressure for fcc ⇆ bcc transformation in ytterbium is below 3·5 GPa. The valence change under pressure has been discussed.

    • Use of energy dispersive method with tungsten carbide opposed anvil high pressure set-up

      A K Singh S Usha Devi

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      The use of energy dispersive method has been discussed to record the X-ray diffraction data from a tungsten carbide opposed anvil high pressure set-up. It is pointed out that a proper collimation of the incident and the diffracted beams can eliminate the scattering from the gasket material. This results in an appreciable improvement in the quality of the recorded diffraction data. The choice of the various parameters has been discussed. The data on sodium chloride are presented in support of this analysis.

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