Pressure-induced H bonding: neutron diffraction study of brucite, Mg(OD)₂, to 9.3 GPa

The structure of deuterated brucite has been refined using Rietveld analysis of neutron powder diffraction data collected in an opposed-anvil high-pressure (Paris-Edinburgh) cell from 0.4 to 9 GPa. On the basis of bond length changes obtained from the structure refinements, H bonding between the octahedral layers becomes more significant as the unit cell contracts. The c axis is approximately two times as compressible as the a axis in this pressure range, and the compression along c is largely taken up by a 13% reduction of the interlayer spacing. The O-D bond length, on the other hand, remains nearly constant or increases slightly over the pressure range. The position of D was modeled as a threefold split site of one-third occupancy each. -from Authors