The Hunt for Hydrogen in the High-Pressure Phase of Ca(OH){sub}2 and Ca(OD){sub}2: Neutrons Versus X-Rays

摘要

A recent measurement on the high-pressure phase of Ca(OH)2 using high-resolution synchrotron X-ray powder diffraction has been carried out on a hydrogenated sample at high-temperature. It complements an earlier time-of-flight neutron measurement carried out in the US on a deuterated sample at low temperature. The two protons are found by Rietveld refinement using a new suitable non-Fourier based strategy, for which GSAS and FullProf yield very similar results. Our X-ray result agrees with the previous neutron study for one proton site only, prompting us to reinvestigate the neutron data. A second new and distinct non Fourier-based strategy coupled with GSAS is used to tackle the latter data and indeed confirms the US results. Whilst the reasons for this X-Ray vs Neutron discrepancy can only be guessed at this stage, the use of the two related proton-finding strategies could be extended beyond our specific study.