ANOMALOUS RESISTIVITY PEAKS, LOCALIZATION TRANSITIONS, AND THE ELECTRONIC-STRUCTURE OF SUBSTOICHIOMETRIC LANTHANUM TRIHYDRIDES

The resistivity (T) of LaHx (2.80x2.90) was determined from Q-factor measurements at 100 K<T<700 K. Its temperature coefficient >0 is small at T200 K, and (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 (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 24020 K. © 1990 The American Physical Society.