Anomalous resistivity peaks, localization transitions, and the electronic structure of substoichiometric lanthanum trihydrides

The resistivity {ρ}(T) of LaHₓ (2.80{≤}x{≤}2.90) was determined from Q-factor measurements at 100 K 0 is small at T{≤}200 K, and {ρ}(T) peaks at some T between 220 and 260 K. The peak narrows with increasing x and is extremely sharp for x{≥}2.86. At higher temperatures the behavior of {ρ}(T) is consistent with variable-range hopping. It is suggested that a delocalized band of states at EF, associated with the superlattice of octahedral vacancies, becomes localized and its mobility is quenched when the superlattice collapses above {~}240±{}20 K.