A metal-semiconductor transition has been observed in the range 230–260 K for the first time in a slightly superstoichiometric rare-earth dihydride, ${\mathrm{YH}}_{2.10}$ (as compared to the x-rich systems ${\mathrm{CeH}}_{2+\mathit{x}}$ and ${\mathrm{LaH}}_{2+\mathit{x}}$ with 0.7≲x≲0.9), implying an order-disorder transformation in the octahedral sublattice of the excess hydrogen atoms as the driving mechanism. Furthermore, a resistivity minimum in the range 60–80 K was observed, indicating for the first time in such systems an additional metal-semiconductor transition towards lower temperatures.

• Received 1 February 1991

DOI:https://doi.org/10.1103/PhysRevLett.66.3176