The Alkali Elements at Extreme Compressions: Static and Dynamic Compression Techniques

The alkali elements have been a "hot" topic in high pressure research for the last decade. Nearly-free electron metals at ambient pressure, they show a remarkable departure from this "simple" behaviour with pressure. Complex, low-symmetry, open-packed structures have been observed in Li, Na, K, Rb and Cs. Anomalous melting, where the gradient of the melting curve (dT/dP) becomes negative over large pressure regions, has been observed in Rb, Cs, Na and Li, but had not been observed in K. We have used static compression techniques (diamond anvil cell) to re-examine the melting curve of K.

Although a vital tool in high-pressure research the pressure and temperature conditions achieved with the diamond anvil cell technique have not typically exceeded 400 GPa and several thousand Kelvin, leaving many exotic states of matter, including those in the alkali metals, tantalizingly out of reach. A method to get beyond this limit is by using extremely powerful lasers to ramp- or shock- wave compress materials. Here recent data on the ramp- and shock-wave compression of Na will be presented.