We have shown that "new" elements (2) such as potassium, although alkali elements at ambient pressure, can react chemically like a transition element with a single electron in a d-orbital upon compression to gigapascal pressures. Unusual graphite-like sheets (see AgK2 figure) of potassium atoms (red) intercalated with silver atoms (black) in AgK2 can form, for example (3).
We have also investigated carbon materials such as the sp3-bonded "transparent phase", a new form of carbon (4) that forms upon compression of (sp2-bonded) graphite (5), networks formed from benzene molecules (6), diamond formed directly from C60 at ambient temperature (7), and carbon nitrides (8). Multiwavelength Raman spectroscopy (9) with excitation wavelengths from the deep UV to the near IR has proved to be a powerful tool for characterizing these materials. The insights from these curiosity driven studies of carbons reversible rehybridization behavior may help in the search for improved hydrogen storage materials, new phases of carbon and high strength carbon materials.
Materials Discovery by Pressure Tuning
We have used pressure for a "combinatorial" approach to complex materials discovery because fundamental parameters such as orbital overlap can be tuned very precisely and over a wide range (1). For example, our pressure tuning experiments have shown that the product of the temperature and dimensionless figure of merit (ZT) of the most technologically important thermoelectric material, antimony bismuth telluride, can be doubled from ~1 to ~2. (10). These studies may provide insight into how to reproduce this record ZT at ambient pressure.