K Govinda Rajan
Articles written in Pramana – Journal of Physics
Volume 18 Issue 1 January 1982 pp 1-15 Experimental Techniques And Instrumentation
The Bridgman anvil technique offers a simple and versatile means of generating very high pressures required in solid state studies. The opposed anvil technique is based on the principle of massive support. The practical case of a gasketted anvil is considered, and an expression for the maximum pressure generated under massive support is derived in terms of the geometric parameters, the strength of the anvil material and the gasket properties. In particular, for a given maximum pressure, it is possible to calculate the taper angle, the taper height and the gasket thickness from this expression. The anvil is assumed to be in the elastic region under load. Good agreement is obtained between the calculated and the experimental values for the massive support factor (
Volume 24 Issue 6 June 1985 pp 825-835 Experimental Techniques
A high pressure-high temperature cell which permits
Volume 26 Issue 2 February 1986 pp 151-159 Experimental Techniques
Copper crystals have been grown by Czochralski technique in a 6-bar argon gas environment. X-ray analysis shows that these are single crystals and are strain-free. A slight pressure environment that is truly hydrostatic seems to improve the quality of the crystals. Thermal profile estimation results show that the values of temperature which decrease upto the neck region are same in magnitude as those measured during the experiments and that necking improves the thermal profile and, consequently, the crystal quality. No facet formation has been observed in these crystals.
Volume 33 Issue 6 December 1989 pp 667-672 Condensed Matter Physics
This paper reports the phase transformation behaviour of tetracyanoethylene (TCNE) under pressure as revealed by AC electrical resistivity, its time evolution and X-ray diffraction studies. An irreversible transformation from monoclinic to cubic phase occurs at 2.1±0.1 GPa and is indicated by a sharp resistivity drop at this pressure. The time evolution of resistivity studies indicate that this transformation occurs via an intermediate phase having resistivity higher than either of the two crystalline phases. Finally, the kinetics of phase transformations obtained by time evolution of resistivity is compared with the X-ray studies on the pressure quenched TCNE.
Volume 40 Issue 5 May 1993 pp 367-376
We report the diamond anvil cell (DAC) high pressure powder X-ray diffraction studies on amorphous selenium (a-Se) under truly hydrostatic pressure condition up to 20 GPa. Amorphous selenium exhibits a sharp and irreversible transition to a hexagonal structure at 10.6 ± 0.1 GPa. It is also known that metallization occurs in a-Se around this pressure. Some plausible arguments are provided to suggest that the amorphous to crystalline transition may be driven by metallization.
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