Quantum effects in lithium metal

Figure caption: Observed stable and metastable crystal structures of <sup>6</sup>Li and <sup>7</sup>Li measured along the identified P-T paths.
Figure caption: Observed stable and metastable crystal structures of 6Li and 7Li measured along the identified P-T paths.

For decades it has been believed that lithium, the simplest metallic element, has a complicated ground-state crystal structure. Using synchrotron x-ray diffraction at HPCAT and multiscale simulations with density functional theory and molecular dynamics, a research group has shown that the previously accepted martensitic ground state is metastable. The new ground state is face-centered cubic. The group shows that different isotopes of lithium (6Li and 7Li) display crystal phase transitions at slightly different pressures and temperatures under similar thermal paths, which could be related to large quantum mechanical effects between the isotopes. Lithium is an extremely challenging material for high-pressure studies: It reacts chemically with many materials (e.g., it causes gasket metals and diamonds to become brittle), and diffraction experiments are challenging because of low scattering cross sections. The new results present a comprehensive picture of how the quantum interplay of the nuclei and electrons leads to surprising and hitherto unsuspected behavior in this simplest of metallic elements. More in G. J. Ackland et al, Science, 356, 1254, 2017