Condensed matter chemistry under ‘extreme’ high pressure–high temperature conditions

Abstract

Improved techniques for high-pressure experiments have led to new studies of the structure and physical properties of materials compressed to extremely high densities. Now we must fully enable the field of condensed matter chemistry under extreme high-pressure conditions. This will require development of strategies for the analysis and control of the chemical composition during reactions between solid, liquid and fluid phases. Such approaches already exist within the fields of experimental geochemistry and petrology, and they can be readily adapted to the wider area of chemistry. The first consideration is the manipulation and determination of stable and metastable pressure–temperature phase diagrams, illustrated here for the one-component system Si. Next, relationships between P, T and the chemical composition, X, expressed in terms of the chemical potential (μ) or the activity–composition relations, can be used to constrain and determine components within the system. This is illustrated by examples drawn from our recent work on high-pressure syntheses of boron suboxides (B₆O_1 − δ) and (Si, Ge)₃N₄ nitride spinels.

Keywords:

• High pressure
• Solid-state chemistry
• Silicon
• B6O
• Ge3N4
• Phase relations
• Negative pressure

Acknowledgements

PFM acknowledges support from the EPSRC, the Wolfson Foundation and the Royal Society. He thanks E. Soignard, C. Bull, D. Daisenberger, T. Chaplin, S. Farag, and A. Pugsley for their help in establishment of the high-pressure and solid-state chemistry laboratories at UCL and at the RI, and for the preliminary results obtained within our London-based group for high-pressure solid-state chemistry research that are presented here as examples. Thanks are also due to John Holloway for a careful review of the article.