High Pressure Melting of Lithium

CREDIT

For over two years, since we started our lab, we have been trying to measure the high pressure melting curve of lithium. Lithium is the lightest metal under ambient pressure. Because of its low atomic number and metallic properties, lithium has been considered for studying the dominant lattice quantum zero point energy in condensed matter and under compression.

 

The project was a challenging problem. In general, measurements of melting curves of materials under high pressures, hundreds of thousands of atmospheres, are very difficult. In the case of lithium, the challenges were amplified since lithium is highly reactive with many materials, including the pressure chamber itself, which is made of precious diamonds. Also, lithium has an unusually low melting temperature under compression which excludes application of many available methods for remote thermometry. State of the art crystallography methods failed to provide solid proof for the melting properties of lithium under pressure.

After trying many different existing methods, we have found a novel method that allowed us to accurately measure the melting of lithium to pressures above half million atmospheres. The experiments were arduous and required several of months of around the clock experimental runs. The experiments were successfully completed by a team of students led by graduate student Anne Marie Schaeffer and two undergraduate students William Talmadge, now a graduate student, and Scott Temple. The results appeared in the November issue of Physical Review Letters.

In our recent studies, we have discovered a new lithium based superconductor, BaLi4, which becomes superconducting under pressures lower than both parent compounds. The results of this work, which has been led by Anne Marie Schaeffer in collaboration with Sivaraman Guruswuamy, is currently under review. The other coauthors of this work are Matthew DeLong, Zachary Anderson, and William Talmadge.