Crystal structure and some transport properties of Na-doped LaMnOy

The crystal structure, electrical resistivity (ρ), magnetoresistance (MR) and Seebeck coefficient (S) of La1−xNaxMnOy   (x=0.075x=0.075, 0.1, 0.125,0.15, and 0.175 at%) are investigated. La1−xNaxMnOy crystallizes in a single-phase rhombohedral structure. The temperature dependence of the resistivity with and without magnetic field shows a metal–semiconductor transition at Tm, which depends on the Na content. We determine the activation energy Eρ in the semiconductor region. The magnetoresistance MR has a negative sign. The sign of S changes from positive to negative as T increases and S becomes more negative at high concentrations of Na doping.