Raman spectroscopy as a probe for <i>in situ</i> studies of pressure‐induced amorphization: some illustrative examples

Abstract

Abstract The main models proposed in the literature to describe pressure‐induced amorphization (PIA) are briefly reviewed, with special emphasis on the kinetic aspects of PIA. The high potential of Raman spectroscopy for experimental studies on PIA is highlighted and illustrated by the results obtained for zirconium tungstate (ZrW 2 O 8 ) and boric acid (H 3 BO 3 ). Compared with x‐ray diffraction using a conventional x‐ray tube, Raman spectroscopy allowed a much faster identification of the transitions in both compounds. Further, the Raman results for ZrW 2 O 8 have given support to an amorphization mechanism based on the freezing of low‐energy vibrational modes associated with rigid (or quasi‐rigid) ZrO 6 and WO 4 polyhedral units. For H 3 BO 3 , we obtained strong evidence of a PIA associated with hindered decomposition of H 3 BO 3 , probably to a mixture of HBO 2 and H 2 O. The short acquisition time for the Raman measurements of samples under high pressure enabled us to follow the kinetics of the transition on H 3 BO 3 , which could hardly be done by conventional x‐ray diffraction. Raman spectroscopy proved to be a very convenient technique to study the mechanisms behind PIA, owing not only to the fast acquisition of information about phase transition kinetics, but also to the structural information that can be obtained. Copyright © 2003 John Wiley &amp; Sons, Ltd.