Andrea Di Cicco
INFM, Dipartimento di Matematica e Fisica, Universita' di Camerino, via Madonna delle Carceri, 62032 Camerino (MC), Italy. URL: http://gnxas.unicam.it.
E-mail: dicicco@unixas.unicam.it
Beamlines: DW11 (WDIS)
Phase transitions in submicrometric Ga droplets confined in epoxy resin have been studied [1] by combining energy-dispersive x-ray diffraction (EDXD), x-ray absorption fine structure (XAFS) and single-energy x-ray absorption. EDXD measurements have been collected at beamline DW11 in the framework of the projects ``Structure of liquid and solid metals under extreme conditions'' and ``High-pressure High-temperature Phase Diagram of Ga and Bi''. The help of J. P. Itie' and F. Baudelet was essential in obtaining and placing the He cryostat into the hutch for EDXD experiments.
The low-temperature diffraction measurements of Ga performed at LURE provided key information to identify and study the structure of the metastable phases and understand the complex high-pressure behaviour. Accurate XAFS and single-energy x-ray absorption measurements were performed at the ESRF (BM 29) under similar thermodynamic conditions. The new XAFS data published in [1,3] follows similar experiments performed at LURE with lower resolution [2].
We found that the restricted fluid is undercooled down to 150 K while the melting point is depressed down to 254 K. Melting and freezing are sharp both sharp processes occurring with temperature broadening of 1 K and 10 K respectively. EDXRD patterns are consistent with that of b-Ga, while the stable phase at ambient conditions a-Ga is not found to exist.
Appearance of g-Ga and d-Ga solid phases and relevance of present results to recent studies of Ga confined in porous glass are discussed in ref. [1].
[1] A. Di Cicco, ``Phase Transitions in Confined Gallium Droplets'', Phys. Rev. Lett. 81, 2942 (1998).
[2] A. Di Cicco and A. Filipponi, ``Local correlations in liquid and supercooled gallium probed by x-ray absorption spectrocopy.'', Europhys. Lett. 27, 407 (1994).
[3] A. Di Cicco, S. Fusari, and S. Stizza, ``Phase transitions and undercooling in confined gallium''
Phil. Mag. B 79, 2113 (1999).