Metastable phase transitions and structural transformations in solid-state materials at high pressure

Abstract

We use a combination of diamond anvil cell techniques and large volume (multi-anvil press, piston cylinder) devices to study the synthesis, structure and properties of new materials under high pressure conditions. The work often involves the study of structural and phase transformations occurring in the metastable regime, as we explore the phase space determined as a function of the pressure, temperature and chemical composition. The experimental studies are combined with first principles calculations and molecular dynamics simulations, as we determine the structures and properties of new phases and the nature of the transformations between them. Problems currently under investigation include structural studies of transition metal and main group nitrides, oxides and oxynitrides at high pressure, exploration of new solid-state compounds that are formed within the C-N-O system, polyamorphic low- to high-density transitions among amorphous semiconductors such as a-Si, and transformations into metastable forms of the element that occur when its “expanded” clathrate polymorph is compressed.

Keywords:

• High pressure
• Solid state chemistry
• Metastable transitions
• Transition metal nitrides
• Silicon clathrates

Acknowledgements

PFM acknowledges support from UCL and the Davy-Faraday laboratory of the RI as well as the EPSRC through grants GR/R65206 and S78704. These grants enabled construction of the high-pressure laboratory and supported our initial studies of nitride and oxynitride materials at high pressure, including “light element” phases. The awards are now superceeded by an EPSRC Portfolio partnership on “Synthesis, Design and Function in New Materials Chemistry” (EP/D504782/1), held jointly with CRA Catlow (RI/UCL) and P Barnes (Birkbeck College). PFM's group in high-pressure research, especially liquid- and amorphous-state polyamorphism, was supported by a Wolfson-Royal Society Research Merit Award. Recent work to develop high-pressure solid-state chemistry and materials science research is supported by an EPSRC Senior Research Fellowship award (GR/T00757). We acknowledge the many contributions of former students and post-doctoral associates and collaborators, especially Emmanuel Soignard, Craig Bull, Kurt Leinenweber, Tracey Chaplin, Tetsuya Kawashima, Gouyin Shen, Martin Wilding and Jan Gryko, for helping to establish the UCL and RI laboratories for high pressure solid state chemistry and materials research, providing samples for study and for experiments at synchrotron and neutron beamlines.