Russell J. Hemley and Ho-kwang Mao

2005 Balzan Prize
Pressure-induced amorphization began to be reported in a broad range of materials,
as other groups began to study the effect. A major problem in this work
was associated with an inability to probe the materials over a sufficient range of
length scales and with the lack of in situ techniques. This problem was solved in
a series of microscopy studies carried out with Kathleen Kingma; these studies
directly revealed the range of length scales associated with the transformation
[Science 259, 666 (1993)], the existence of a metastable intermediate phase [Phys.
Rev. Lett. 70, 3927 (1993)] and the complexity of the proposed glasses formed
in this way [Phys. Rev. Lett. 72, 1302 (1994)]. The existence of an intermediate
phase remained the subject of a great deal of subsequent theoretical papers by
condensed matter theorists. Brillouin scattering measurements confirmed the
elastic instability hypotheses for quartz specifically [Phys. Rev. Lett. 84, 3117
(2000)]. Pressure-induced amorphization is now documented in a broad range
of materials; in addition to the novel dynamical aspects of the problem, it offers
a new route for the synthesis of new materials with novel physical properties. 34
The work on amorphization led to the discovery of new phenomena in related
systems. The observation of amorphization of ice mentioned above had been reported
using quench techniques. However, the transformation was not monitored
directly; hence numerous questions remained with regard to the actual
transformation, including its mechanism. Using newly developed in situ techniques,
the transition sequence was directly observed and monitored by optical
spectroscopy for the first time [Nature 338, 638 (1989)]. The study revealed the
mechanism of the transformation, proof that the high-pressure phase was indeed
amorphous and the pressure-temperature limits of high-density amorphous ice.
Moreover, this exhaustive study revealed that this fundamentally important system
– H 2O – is far richer than previously anticipated, revealing numerous new
and unexpected transformations as a function of pressure and temperature. Aspects
of this work were confirmed by others working in this field much later, including
neutron studies carried out in the early 1990s, 35 as well as in very recent
research. 36 In later work, another class of metastable transformations was revealed
through these spectroscopic techniques [Science 281, 809 (1998)]. Together
with the later higher pressure studies transformations discussed below
[Science 273, 218 (1996); Phys. Rev. Lett. 78, 4446 (1997)], the work continues
a tradition of study of the wonders of water and ice begun by Gustav Tammann 37
and Percy W. Bridgman 38 over a century ago. 39
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