Crystal structure and some transport properties of Na-doped LaMnOy. .

The crystal structure, electrical resistivity (r), magnetoresistance (MR) and Seebeck coefficient (S) of La1
xNaxMnOy
(x ¼ 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 Er 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.