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New materials from high-pressure experiments


High-pressure synthesis on an industrial scale is applied to obtain synthetic diamonds and cubic boron nitride (c-BN), which are the superhard abrasives of choice for cutting and shaping hard metals and ceramics. Recently, high-pressure science has undergone a renaissance, with novel techniques and instrumentation permitting entirely new classes of high-pressure experiments. For example, superconducting behaviour was previously known for only a few elements and compounds. Under high-pressure conditions, the 'superconducting periodic table' now extends to all classes of the elements, including condensed rare gases, and ionic compounds such as CsI. Another surprising result is the newly discovered solid-state chemistry of light-element 'gas' molecules such as CO2, N2 and N2O. These react to give polymerized covalently bonded or ionic mineral structures under conditions of high pressure and temperature: the new solids are potentially recoverable to ambient conditions. Here we examine innovations in high-pressure research that might be harnessed to develop new materials for technological applications.

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Figure 1: Superhard materials, including several new materials prepared by high-pressure synthesis: both low-hardness (blue) and high-hardness (pink) values within a typically measured range are shown.
Figure 2: Bulk modulus plotted against unit cell volume (per metal atom) for highly incompressible metals and compounds.
Figure 3: A generalized free-energy/high-pressure diagram for a material that undergoes a phase transition into a high-density form.
Figure 4: A hypothetical phase diagram for silicon under positive and negative P T conditions, from combined results of high-pressure and synthesis studies in stable and metastable regimes, and ab initio calculations and simulation results.


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P.F.M. is a Wolfson–Royal Society Research Merit Award holder.

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McMillan, P. New materials from high-pressure experiments. Nature Mater 1, 19–25 (2002).

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