C S Sundar
Articles written in Bulletin of Materials Science
Volume 2 Issue 3 August 1980 pp 207-216
Positron lifetime has been measured in SmS under external pressures from 0 to ∼ 16 kbar, and in (Sm0·8Gd0·2)S at temperatures from 10 K to 300 K. An abrupt drop in the lifetime was observed at the valence transition at a pressure of 6·5 kbar in SmS and at a temperature of ∼ 120 K in (Sm0·8Gd0·2)S. Measurement of the Doppler broadening of the annihilation photons was made in (Sm0·8 Gd0·2)S as a function of temperature. The line shape parameter of the Doppler broadened spectrum also showed an abrupt change at the transition. Angular correlation of annihilation photons was measured in the semiconducting phase of SmS and in the metallic phase of (Sm0·8Tb0·2)S. The correlation profile in the mixed valence (metallic) phase was broader than that in the semi-conducting phase. These results have been explained on the basis of the electronic structure of the semiconducting and the metallic phases of these materials.
Volume 17 Issue 7 December 1994 pp 1215-1232
The application of positron annihilation spectroscopy to the study of defects in materials is illustrated through several examples drawn from our work. These include the study of vacancy clustering in metals, clustering of He atoms to form bubbles, and solute clustering in alloys. Results of studies on novel materials such as quasicrystals, cuprate superconductors and fullerenes are also presented.
Volume 20 Issue 4 July 1997 pp 377-377
Volume 20 Issue 4 July 1997 pp 535-540
Al61·4Cu22·7Fe15·9, Al63·2Cu21·8Fe15 and Al71Cu14Fe15 have been studied by Mössbauer, positron annihilation and X-ray diffraction techniques. The positron lifetime, measured as a function of temperature, in Al61·4Cu22·7Fe15·9 shows a two-step increase. This is found to be due to the dynamics of phasons associated with Al and Cu, having activation energies of 0·43 eV and 0·78 eV respectively. In the case of Al71Cu14Fe15, a phase transformation from the quasicrystalline-crystalline phase at ≈ 550°C is observed.
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