The effect of cation disorder on electrical transport properties of Nd0:7(Ca, Sr, Ba)0:3MnO3

The electrical transport properties of a series of samples, Nd0.7(Ca,Sr,Ba)0.3MnO3, with a fixed average A-site cation radius rA have been studied. Infrared spectra revealed that the symmetry of the local MnO6 octahedra reduces due to the size differences between various A-site ions. From the metal transition temperature Tm up to room temperature, the variable-range-hopping conduction mechanism has been observed, and Tm exhibits a systematic decrease with increasing A-site cation disorder. In the very-low-temperature range, we have observed that resistivity increases with decreasing temperature.