Metal-semiconductor transition and crystal structures of ternary lanthanide hydrides
In contrast to other Laves phases lanthanide containing LnMg2 (Ln = La, Ce, Sm, Eu) show a metal-semiconductor transition upon hydrogenation and formation of LnMg2H7 and EuMg2H6. Recently we found new hydrides of Laves phases LnMg2 (Ln = Nd, Eu, Tb). NdMg2H7 seems to be isotypic to LaMg2D7 according to laboratory X-ray diffraction. EuMg2 forms intermediate hydrides with crystal structures similar to that of the parent hexagonal Laves phase, which are of particular interest in view of the metal-semiconductor transition. TbMg2 behaves similar, but crystallizes in a monoclinic space group. In addition to these Laves phase hydrides, two further lanthanide hydrides need completion of their crystal structure; these are Eu2RuH6 (probably K2PtCl6 type) and YbD2.67, where the ordering of deuterium atoms is under debate. All powders will be investigated at D20 at room temperature. The high neutron absorption of europium requires a short wavelength (0.8A) and the use of double-walled sample holders. All other samples will be measured at 1.87A in high-resolution mode. The YbD2.67 sample will be measured in situ at 100 bar deuterium pressure in a user supplied gas pressure cell.
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Holger Kohlmann; FINGER Raphael; Thomas C. Hansen and WERWEIN Anton. (2016). Metal-semiconductor transition and crystal structures of ternary lanthanide hydrides. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.5-21-1103
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