Strain effect on the transport properties of epitaxial PrNiO3 thin films grown by polymer-assisted deposition

Abstract

Epitaxial PrNiO3 (PNO) thin films were grown on single-crystal LaAlO3, (LaAlO3)0.3(SrAlTaO6)0.7, and SrTiO3 substrates, respectively, by the polymer-assisted deposition method. It is found that compared with that of PNO bulk, the c-axis parameter of PNO film increases under compressive strain and decreases under tensile strain. Moreover, under tensile strain, the c-axis first decreases and then increases. All the PNO films exhibit metal–insulator (MI) transition with a thermal hysteresis in the temperature-dependent resistivity. At room temperature, the resistivity of the PNO films shows an increasing trend with the lattice mismatch strain changing from compressive to tensile. The MI transition temperature TMI of the PNO films under both compressive and tensile strains is lower than that of PNO bulk. However, the trend of TMI dependent on the lattice mismatch between the film and the substrate under tensile strain is decreasing. The conduction mechanism fits very well with the Mott’s variable range hopping (VRH) model in temperatures below 35 K. It is suggested that strain relaxation increases with the strain increasing from compressive to tensile, which results in the increase of oxygen vacancies compensated by more Ni2+ changed from Ni3+ in the film. The competing and joint effects of the bending of the Ni–O–Ni bond angle, the elongation of the Ni–O bond length, and the change of Ni valence dominate the transport properties of the PNO films.