• V Shubha

      Articles written in Bulletin of Materials Science

    • Critical phenomena in solids

      V Shubha

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      In general a solid-solid phase boundary does not terminate in a critical point due to symmetry requirements. However, there exists systems like pure cerium metal and rare earth compounds like samarium sulphide where an isostructural solid-solid phase boundary terminates at a critical point. The critical point for the pressure-induced semiconductor-metal phase transition in SmS has been determined for the first time using the thermoelectric power data collected upto 12 kbar pressure and 850° C. These results are discussed on the basis of some theoretical models developed for the mixed valent compounds.

    • Mercury chalcogenides under pressure

      T G Ramesh V Shubha P S Gopalakrishnan

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      The mercury chalcogenides, HgTe and Hg1−x Cdx Te, have received considerable attention in recent years because of their use in infrared photon detectors. This article is concerned with some recent experiments on the Γ68 band crossover in these systems induced by pressure. It is shown that although the inverted band model is valid for HgTe, the conclusions of the earlier workers on the pressure induced Γ68 crossover are erroneous. Experimental results show that it is difficult to observe the band crossover due to an intervening structural phase transition from cubic zinc blend to the cinnabar structure. However pressure experiments on the semiconductor alloy system Hg0·9Cd0·1 Te clearly indicate this crossover. New results on the zinc blend-cinnabar phase transformation are also presented. The striking behaviour of thermoelectric power in the high pressure cinnabar phase is correlated with the available experimental data on the structurally similar elemental semiconductors like selenium and tellurium.

    • Pressure-induced band cross-over in Pb1−xSnxTe

      T G Ramesh V Shubha P S Gopalakrishnan

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      Resistivity and thermoelectric power studies have been carried out on two semiconductor alloy systems viz Pb0·8Sn0·2Te and Pb0·6Sn0·4Te up to 35 kbar pressure. Thermoelectric power and resistivity data on Pb0·8Sn0·2Te indicate that the energy gapEg=EL6EL6+ decreases with pressure resulting in a zero gap state near 35 kbar pressure. TEP studies on the alloy system Pb0·6Sn0·4Te provide direct evidence for a pressure induced L6→L6+ cross over transition.

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