ELECTRICAL AND MAGNETIC-PROPERTIES OF LAMO8-XO14 CONTAINING ISOLATED MO-8 CLUSTERS

Single crystal specimens of LaMo8-xO14 (x = 0 and 0.3) suitable for tr ansport property measurements have been prepared by electrolyzing fuse d mixtures of sodium and rare earth molybdates. Electrical resistivity measurements with the current parallel to the ab plane of LaMo8-xO14 containing the quasi-discrete units of Mo-8 clusters showed semiconduc ting behavior down to 20 K for both compounds. The electrical resistiv ity in the ab plane (rho(ab)(300K) = 5 x 10(-3) ohm . cm) of LaMo7.70O 14 is an order of magnitude smaller than the corresponding value for t he fully stoichiometric compound (rho(ab)(300K) - 4.4 X 10(-2) ohm cm) . Furthermore, the rho(ab)(300K) of La Mo7.70O14 is a factor of 4 lowe r than that measured along the c-axis (rho(c)(300K) = 2 X 10(-2) ohm . cm) implying quasi-low-dimensional behavior. The thermal activation e nergy for electrical conductivity estimated from the Inp vs 1000/T plo ts showed a significant decrease near similar to 70 K and 130 K for La Mo7.70O14 and LaMo8O14, respectively. The magnetic susceptibility data collected on a batch of randomly oriented crystals revealed the prese nce of local moments in LaMo7.7O14, while the stoichiometric analogue was diamagnetic. The semiconducting nature of the LaMo8-xO14 phases ma y be attributed to the unfavorable intercluster distance (3.08 Angstro m) as well as positional and configurational disorder of the Mo-8 clus ters. (C) 1995 Academic Press, Inc.