High-temperature resistivity in rare-earth nickelates films

We expand the temperature interval of the resistivity measurement to clarify the charge transport mechanisms in the rare-earth nickelates ReNiO3. Thin films of LaNiO3 demonstrate an expected metallic behavior at high temperatures: a perfect linear rise of the resistivity rho proportional to T is confirmed above room temperature. However, NdNiO3 films characterized by a sharp metal-to-insulator transition display a noticeable deviation of their high-temperature resistivity from the metallic linear relation. This deviation is suggested to originate from an additional thermally activated hopping transport. High-temperature hopping conductivity is also found in SmNiO3 films. Carrier localization due to disorder and the formation of small polarons is discussed as being responsible for hopping.