PROGRESSIVE CHANGE WITH T FROM HOPPING TO RANDOM-PHASE PROPAGATION IN LA2-XNIO4-DELTA (DELTA-GREATER-THAN-OR-EQUAL-TO-0)

Electronic properties of La2-xNiO4-delta (0 less than or equal to x less than or equal to 0.15, 0 less than or equal to delta less than or equal to 0.15) have been investigated for 77 less than or equal to T (K) less than or equal to 800. Charge compensation between La vacancies and O vacancies makes the hole concentration approximately constant in the series. In the low-temperature range, hopping conduction between localized states dominates. The activation energy of this process increases with increasing structural distortion. In the high-temperature range, close to 650 K, both thermal excitation and broadening of the band contribute to make the carriers delocalized and the conductivity a slow function of T. The mobility at 650 K remains low, i.e. 0.3 cm(-2) V-1 s(-1), from which we conclude that the carriers move according to a random phase propagation. In this regime, the O vacancies scatter charge carriers and increase the resistivity.