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) Å and c = 7.58858(4) Å in space group P42/mnm (No. 136); Y3Al2H5.5: a = 8.5043(1) Å, b = 8.3268(1) Å and c = 7.5913(1) Å in space group Pnnm (No. 58); and Y3Al2H6.5: 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 Y3Al2H2.2 were determined by using a powder neutron diffraction and Rietveld analysis of a deuteride Y3Al2D2.33 (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.
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