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; Y₃Al₂H_2.2: a = 8.29744(4) Å and c = 7.58858(4) Å in space group P4₂/mnm (No. 136); Y₃Al₂H_5.5: a = 8.5043(1) Å, b = 8.3268(1) Å and c = 7.5913(1) Å in space group Pnnm (No. 58); and Y₃Al₂H_6.5: a = 12.2544(2) Å, b = 12.1332(2) Å and c = 14.8268(2) Å 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 Y₃Al₂H_2.2 were determined by using a powder neutron diffraction and Rietveld analysis of a deuteride Y₃Al₂D_2.33 (a = 8.2850(3) Å and c = 7.5832(3) Å in space group P4₂/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.