Crystal growth of ytterbium dihydride and the phase relations in the Yb-H system

Abstract

Orthorhombic YbH 1.94 and cubic YbH 2.56 were the only two phases found in the range 250 ° C ⩽ T ⩽ 800 ° C and 0 atm ⩽ P H 2 ⩽ 120 atm. The metastable cubic phase YbH 2.02 reported previously was not detected. Single crystals of YbH 1.75 with dimensions up to 5 mm × 4 mm × 3 mm were grown for the first time in sealed tungsten crucibles by sublimation. A plot of the lattice constants of the cubic rare earth (RE) dihydrides and trihydrides versus the atomic number shows a much larger value for YbH 2.56. Therefore, we conclude that of all the binary cubic RE hydrides only this phase has strong contributions from RE 2+ ((4f) n (5d)° configuration). The possible mixed valence of this phase is discussed. Optical re-emission measurements show that YbH 1.94 is a semiconductor and that YbH 2.56 is metallic. This supports the existence of mixed valence in the latter phase.