Octahedral modifications by Ga doping in NdNiO3 thin films and its systematic influence on electronic transport
摘要
NdNiO3, a perovskite nickelate, exhibits a first-order metal–insulator transition (MIT) with thermal hysteresis. The low temperature insulating behavior is associated with a charge disproportion of Ni2+ and Ni4+ ions resulting from a convergence of Ni3+ ions. To understand the effects of isovalent Ga3+ doping for Ni3+ on the charge distribution and insulating behavior, we prepared thin films of NdNi1−xGaxO3 (x = 0–0.20) on LaAlO3 (001) (LAO) single crystal substrates using the pulsed laser deposition (PLD) technique. Raman spectra show an emergence of a new phonon mode around 697 cm−1 by just 5% Ga-doping at the Ni-site, which strongly intensifies and shows a red shift with further increase in the Ga-doping. This mode belongs to the breathing vibration of NiO6 octahedra and remains observable down to a low temperature of 93 K. The NdNiO3 film shows an MIT around 62 K, and the resistivity of these thin films increases systematically with the increase in Ga doping. However, for x = 0.20, the film shows completely insulating behavior without any transition. These films (x = 0–0.10) show non-Fermi liquid (NFL) behavior in the metallic state, with a temperature exponent n of 4/3. Our results demonstrate that the breathing mode arises by Ga doping, and it enhances the insulating behavior of Ga doped NdNiO3 thin films.