Synchrotron radiation powder X-ray and neutron diffraction studies on novel Y3Al2 hydrides

Crystal structures of Y3Al2 hydrides with dehydriding/rehydriding properties were clarified using synchrotron radiation powder X-ray diffraction measurements; Y3Al2H2.2: a = 8.29744(4)angstrom and c = 7.58858 (4)angstrom in space group P4(2)/mnm (No. 136); Y3Al2H5.5: a = 8.5043(1)angstrom, b = 8.3268(1)angstrom and c = 7.5913(1)angstrom in space group Pnnm (No. 58); and Y3Al2H6.5: a = 12.2544(2)angstrom, b = 12.1332(2)angstrom and c = 14.8268(2)angstrom in space group Ibam (No. 72). All the hydrides maintain the characteristic metal atom arrangements of Y3Al2 that are composed of distorted W (body-centered-cubic; bcc)- and AlB2-type slabs. Two H atom sites in Y3Al2H2.2 were determined by using a powder neutron diffraction and Rietveld analysis of a deuteride Y3Al2D2.3 (a = 8.2850(3)angstrom and c = 7.5832(3)angstrom in space group P4(2)/mnm (No. 136)). One of these sites is inside a tetrahedron coordinated by four Y atoms and located on both sides of the faces shared by the distorted W-type slabs. The other site is inside a triangle coordinated by three Y atoms and located on one side of the faces shared by the distorted AlB2-type slabs. (C) 2009 Elsevier B.V. All rights reserved.