J. Phys. IV France 7 (1997) C2-983-C2-985
Semi-Conductor to Metal Transition in Liquid Selenium at High Pressure and High TemperatureY. Soldo1, J.L. Hazemann1, 2, D. Aberdam1, E. Pernot2, M. Inui3, J.F. Jal4, K. Tamura3, J. Dupuy-Philon4 and D. Raoux1
1 Laboratoire de Cristallographie-CNRS, 25 avenue des Martyrs, BP. 166, 38042 Grenoble cedex 09, France
2 LGIT CNRS, UJF, BP. 53X, 38041 Grenoble, France
3 Faculty of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima 739, Japan
4 Département de Physique des Matériaux, UCB Lyon I, France
Near its critical point (385 bars, 1615 °C), semiconducting liquid Se gives way to a metallic state (SC-M transition). In this paper we report for the first time XANES and EXAFS measurements on liquid Se in the temperature and pressure range up to 600 bars and 1500°C, in the temperature interval where the electrical conductivity shows the SC-M transition. Both the XANES spectra and the Fourier transforms of the EXAFS modulations present significant modifications. The results obtained with an anharmonic analysis (cumulant expansion method) show that the helical chains get shorter as temperature raises, but, even at the highest temperatures, they are not shorter than 5 atoms. The reconstruction of the distances distribution function for the first shell shows that, in the metallic region, the mean distance value decreases down to about 2.23 Å and the distributions show an important asymmetry towards lower values of R.
© EDP Sciences 1997