DEUTERIUM SITE OCCUPANCY IN YDX BY MAGIC-ANGLE-SPINNING NMR

Magic-angle-spinning (MAS) deuterium NMR of YDx, x similar to 2 yields spectrally resolved lines for D atoms in tetrahedron (T) and octahedr al (O) interstitial sites. Compared to MAS line narrowing of metal hyd rides, the deuterides line narrow with only modest, readily attainable spinning speeds. This is the first application of NMR to resolve ineq uivalent sites in these systems. For YDx at 200 K we find only T sites occupied for x less than or equal to 2.00, in contrast to some other reports. For x > 2.00, the excess D atoms are accommodated in O sites. Thermally activated motions that interchange D atoms between T and O sites are detected and their rate determined, with E(a) = 0.55 eV (=k( B)x6390 K). A third deuterium species, T-O, is spectrally identitifed: D atoms in T sites with occupied O site nearest neighbors. We expect the deuterium MAS-NMR technique to be valuable for site occupancy dete rmination in deuterides of alloys and compounds in which there are sev eral inequivalent occupied sites.