Diagnosing Electride Formation in Ca up to 40 GPa with XANES and SCXRD

It is an open question if all materials will trap electrons in interstitial sites under compression, forming high pressure electrides (HPE) [Miao2014, Racioppi2023]. Molecular and inorganic electrides at ambient conditions have been studied for decades [Wagner1993, Zurek2009]; however, no experiments have probed their electronic structure at extreme conditions. X-ray absorption near edge structure (XANES) is sensitive to the electron energy states around the Fermi energy and is therefore sensitive to how the band structure will change during HPE formation, while single crystal x-ray diffraction (SCXRD) can detect the excess of electron density in the interstitial sites by comparing observed and calculated structure factors. In this experiment, we propose to compress calcium into the simple cubic (sc) HPE phase above 35 GPa and probe the samples using XANES to characterize the electronic structure and SCXRD to confirm the nature of the electride state.