RESISTIVE BEHAVIOUR OF PrH2 + //xCOMPOUNDS AT THE APPROACH OF THE METAL-INSULATOR TRANSITION.

Electrical measurements for PrH//2// plus //x compounds with 0 less than equivalent to x less than equivalent to 0. 75 show a metallic behavior below room temperature. There is strong evidence in favor of structural ordering (short range for x less than 0. 1 and long range for x greater than 0. 2) within the H sublattice for all concentrations x. A qualitative analysis of the phonon resistivity and of the disorder resistivity implies a strong reduction in the carrier density with increasing x; this places this system near to a metal-insulator transition as in CeH//2// plus //x and LaH//2// plus //x. We observe also that the mobility of the H atoms increases with increasing x.