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College Park, Maryland      June 6 - 10 , 2004

TP4: Neutron diffraction of ZrBe2D1.5, ZrBe2Hx and inelastic scattering studies of hydride phases in ZrBe2H0.6

Z. Chowdhuri (NIST Center for Neutron Research; University of Maryland, College Park), R.L. Cappelletti, T.J. Udovic, Q. Huang (NIST Center for Neutron Research)

ZrBe2 has the P6/mmm structure (also found in MgB2) consisting of triangular nets of Zr separated by honeycomb nets of Be. The hydrides ZrBe2Hx display a phase having the same structure in which H diffuses among the honeycomb interstitial sites in the triangular Zr planes. Phases with ordering of the H atoms on a sublattice of the honeycomb appear below an ordering temperature that depends on x. The results of neutron quasielastic scattering measurements made at widely different resolutions on two spectrometers (DCS: FWHM 64 μeV, and HFBS: FWHM 1 μeV) are reported on a powder sample of the ZrBe2H0.6. The data for all momentum transfers (0.3 -1 to 1.7 -1) at each temperature are analyzed in terms of a one-parameter model for independent particle hopping on a honeycomb lattice for the quasielastic portion and an additional elastic term. Monte Carlo calculations verify the validity of the independent particle approximation at this concentration. This work utilizes facilities supported in part by the National Science Foundation under Agreement No. DMR-0086210.

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