NA0.5LA0.5RUO3 - STRUCTURE AND ELECTRONIC-PROPERTIES

A compound Na0.5La0.5RuO3 has been synthesized by the solid-state reac tion method. It crystallizes in the perovskite structure with a lattic e parameter a = 3.8874(1) Angstrom and space group Pm3m. The large cat ions Na+ and La+ are randomly distributed at the A sites, and no struc tural ordering has been found. All samples, prepared at different post -treatment conditions, exhibit good conduction over the temperature ra nge from 4.2 K to room temperature, with a resistivity similar to 2-7 m Omega cm. A crossover from metallic transport to a semiconductinglik e transport with decreasing temperatures, characterized by a minimum r esistivity rho(min) in the rho-T curves, was observed for some samples . The temperature dependence of resistivity at T > 50 K is very weak, \d rho/dT\ < 5 x 10(-3) m Omega cm/K, regardless of the metallic or th e semiconductinglike transport. At low temperatures, the temperature d ependence of resistivity for all samples can be described by a three-d imensional variable-range-hopping conduction due to the hopping betwee n localized states near the Fermi energy in an inhomogeneous medium. T he measurement of the magnetization indicates that there is no magneti c order in Na0.5La0.5RuO3 from 250 K down to 5 K. Instead, the magneti c susceptibilities obey well the Curie-Weiss law. The fitted effective moment and Weiss temperature are p(eff) = 293(1)mu(B) and Theta = -24 3.5(1) K. The Pauli paramagnetic susceptibility chi(pauli) is estimate d to be similar to 1.43 x 10(-4) emu/mole Ru. Moreover, we found that at low temperatures the susceptibility still obeys the Curie-Weiss law , but with a reduced Curie constant. The observed transport and magnet ic data can be understood based on a qualitative density-of-states mod el, combined with the Anderson localization.