Synthesis and Characterization of Calcium Hydrides at High Pressure-Temperature Conditions*

With the report of high temperature superconductivity in H₃S¹ and the success of the theoretical predictions accompanying that discovery², there have been many theoretical predictions of superconductivity in related systems³ as well as other systems. One of the attractive predictions relates to the possibility of clathrate like structures in the calcium system⁴. We report details of our in-situ synchrotron xray diffraction studies on Ca-H mixtures in the pressure range 5-200 GPa and 300-2000 K. At low pressures, not surprisingly, we found that CaH₂ is formed but does not dissociate or transform to any higher hydride. We report results on a very detailed set of in-situ synchrotron XRD experiments carried out at 16-ID-B. Using a combination of theory and experiment, we have identified five different hydrides. Details of these synthesis studies as well as possibility of superconducting phases in these class of hydrides will be presented.

1 Drozdov, A. P., et. al. S. I. Nature 525, 73-76 (2015).
2 Li, Y., et. al . J. Chem. Phys. 140, 174712-174719 (2014).
3 Duan, D. et al. . Scientific Reports 4, 6968, (2014).
4 Wang, H., et. al. Proc. Nat. Acad. Sci. 109, 6463-6466 (2012).