AMBIENT PRESSURE STRUCTURE OF ZrO2-TYPE Ca(OD)2 BY POWDER NEUTRON DIFFRACTION. Kurt Leinenweber1, Dan Partin1, Udo Schuelke1, Mike O'Keeffe1, and Robert B Von Dreele2, Materials Research Group, Department of Chemistry, Arizona State University, Tempe, AZ, 85287-16041, The Manuel Lujan Jr. Neutron Scattering Center (MLANSCE), Los Alamos National Laboratories, Los Alamos, NM, 875452
The high pressure form of Ca(OH)2, isomorphous with monoclinic ZrO2, is known from high pressure in situ powder x-ray diffraction at 8 GPa (Kunz et al., High Pressures, High Temperatures, in press). This phase is unquenchable at room temperature, reverting to the CdI2-type polymorph at about 1 GPa during decompression.
In the present study, a 170 milligram sample of the high pressure form of Ca(OD)2, synthesized at 10 GPa and 400 C, was recovered to ambient pressure for powder neutron diffraction. The back-transformation to the CdI2 structure was suppressed by chilling the sample with liquid nitrogen during decompression. The sample was transferred to a cryostat and a neutron powder diffraction pattern taken at 11 K Platinum foil which was originally used to wrap the sample was left on as a d-spacing standard.
Rietveld refinement indicates the structure P21/c, a = 5.409 Å, b = 6.104 Å, c = 5.995 Å, [[beta]] = 103.7 . Calcium is in 7-coordination with oxygen, with Ca-O distances ranging from 2.39 Å to 2.59 Å. There are, two O-D bond distances, both close to 1.00 Å. One of the D atoms is hydrogen bonded to an oxygen, with an associated O-O distance of 2.81 Å; the other appears to be nonbonded.