High Pressure Materials
Research in P.F. McMillan's group uses high pressure techniques to synthesise new materials in "large volume" devices (multi anvil, piston cylinder). Precursors for the high pressure syntheses are often obtained from organometallic chemistry. Materials under investigation include high-hardness transition metal nitrides and carbides (Ti(N,C), MoN, NbN) that are also superconducting, borides, Si, Ge and Ga oxides and nitrides, and CxNy phases. The high pressure laboratory within the MCC consists of (a) a home-built 500 ton press fitted with a Walker-style split-cylindrical pressurisation module; (b) a "Depths of the Earth" piston cylinder with different pressure plates permitting experiments up to 4 GPa; (c) a Rockland 1000 ton multi-anvil press with a Walker split-cylinder module. Multi-anvil syntheses are carried out routinely to above 10 GPa and T~1500oC; higher pressures (P ~25 GPa) and temperatures (~2000oC) are obtained for smaller sample sizes in selected experiments. The high pressure syntheses are complemented by in situ studies in the diamond anvil cell that permits spectroscopy and structural studies into the megabar range (P > 1,000,000 atm). Pressurised samples are heated inside the cell using infrared lasers (Nd3+:YAG; CO2) or resistively. Synchrotron X-ray studies allow structural changes to be explored during densification and material parameters such as the compressibility are obtained. The recoverability of new materials synthesised under high-P,T conditions is also established during diamond cell experiments. Experimental studies are complemented by ab initio calculations and molecular dynamics simulations (M. Wilson, UCL).
Research funding for research projects in high pressure solid state chemistry and materials science is currently enabled through grants from the EPSRC (Portfolio award to C.R.A. Catlow, P.F. McMillan and P. Barnes) and the Wolfson Foundation-Royal Society.
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