Andrea Di Cicco, Lucia Comez, Marco Minicucci
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
J. P. Itie' and A. Polian
L.U.R.E., Bat. 209 D, Centre Universitaire Paris-Sud, 91405 ORSAY Cedex.
Beamlines: D11 (XAS 10), DW11 (WDIS).
X-ray absorption spectroscopy (XAS) and x-ray diffraction measurements of Ga, Bi and Zn under high-pressure and high or low temperature conditions have been performed using the dispersive set-up available at LURE.
In a first experiment [1], good quality EXAFS (Extended X-ray Absorption Fine Structure) data near the Ga K and Bi L3 edges have been obtained at room temperature in the 0-8.2 GPa (Ga) and 0-4.4 GPa (Bi) pressure ranges using the XAS dispersive set-up installed at L.U.R.E. and diamond anvil cells as pressure devices.
Data-analysis has been performed using advanced ab-initio methods (GnXAS) [2]. XAS spectra have been shown to be sensitive to phase transitions occurring at high pressures and the short-range pair distribution function g(r) were obtained as a function of pressure both in the liquid and solid phases of pure gallium. In a subsequent experiment, EXAFS spectra near the Ga K-edge have been collected in wider pressure and temperature ranges (namely 0-16 GPa, 298-498 K) and Energy dispersive x-ray diffraction (EDXD) data have been also measured in the same thermodynamical conditions. Occurrence of stable and metastable phases and location of the coexistence lines are discussed in light of the results obtained using both experimental techniques (see [3,4]).
Accurate information about local structure in solid and liquid gallium at extreme conditions is obtained and a new determination of the phase diagram of pure Ga is given [4]. A third experiment on solid Zn under pressure in a wide range of temperatures 50-500 K has been performed. The experiment was aimed to shed light on the occurrence of an ETT (Electronic Topological Transition) under pressure (see for example [5] and ref. therein). A detailed report of this last experiment is in course of preparation [6].
[1] A. Di Cicco, L. Comez, J. P. Itie', and A. Polian, ``High pressure x-ray absorption study of gallium and bismuth'', Science and Technology of High Pressure, Proc. of the AIRAPT-17 international conference (1999) editors M. H. Manghnani, W. J. Nellis, and M. F. Nicol, Vol. 2, 452 (2000).
[2] A. Filipponi, A. Di Cicco ``X-ray absorption spectroscopy and n-body distribution functions in condensed matter (II)'', Phys. Rev. B 52, 15135 (1995).
[3] L. Comez, A. Di Cicco, M. Minicucci, R. Tossici, J. P. Itie' and A. Polian, ``EXAFS study of liquid gallium under high pressure and high temperature'', J. Synchrotron Rad. 8, 776 (2001).
[4] L. Comez, A. Di Cicco, J. P. Itie' and A. Polian, ``High pressure and high temperature x-ray absorption study of liquid and solid gallium'', submitted (2000).
[5] S. Klotz, M. Braden, and J. M. Besson, ``Is There an Electronic Topological Transition in Zinc under Pressure?", Phys. Rev. Lett. 81, 1239 (1998).
[6] A. Di Cicco, L. Comez, J. P. Itie' and A. Polian, unpublished (2001).