Electrical resistivity in carrier-doped RNb3O9 (R = La, Ce, Pr and Nd)

Carrier doping in insulating compounds RNb3O9 (R = La, Ce, Pr and Nd) has been carried out. Electrical resistivities below 300 K were measured for excess R-doped compounds; R1+xNb3O9 (x less than or equal to 0.2) and oxygen-deficient compounds; RNb3O9-y (y = 0.1). All the samples showed de conductivity, however the resistivities were very high, e.g. even the lowest value at 300 K is about 1 Omega cm for CeNb3O8.9. The resistivities of R1+xNb3O9 and RNb3O8.9 varied with temperature holding the relation of In p proportional to (T-0/T)(1/4) indicating Mott variable-range hopping (VRH) conductivity. In both systems, the Ce-containing compounds show much lower resistivities. It is noteworthy that the resistivity of CeNb3O8.9 is much lower than the values for the other RNb3O8.9, two orders in the magnitude at 300 K. (C) 2000 Elsevier Science Ltd. All rights reserved.