Strongly emerging octahedral modifications with Al doping and its influence on the electronic transport in NdNiO3 thin films

Abstract

The temperature-dependent electronic transport and the metal-insulator transition in ABO3 perovskite-type NdNiO3 are highly sensitive to chemical substitutions and lattice-mismatch induced strain in thin films. We synthesized two series of NdNi1-xAlxO3 (x = 0-0.50) thin films on LAO (001) single crystal substrates using the pulsed laser deposition technique: one with varied Al doping level (x = 0-0.50) and the other with fixed doping (x = 0.5) but different thickness (10-200 nm). Substituting Al at Ni-site modifies the Ni oxidation state, as observed by x-ray photoelectron spectroscopy. A Raman mode around 693 cm−1 emerges with just 2% Al-doping at the Ni-site, which is otherwise absent in undoped NdNiO3 film. This mode is associated with an anti-stretching of BO6 octahedra in perovskites. With increasing doping, this mode strongly emerges in a dominating manner in the spectra, clearly indicating a further enhancement of octahedral anti-stretching. This mode exhibits a blue shift with increasing Al doping and a red shift with increasing thickness at x = 0.50. Temperature-dependent Raman spectra, analyzed using Balkanski and Grüneisen models, reveal anharmonicity and Red-shifting behaviors. The undoped film shows a metal-to-insulator transition temperature (TMI) of ∼77 K, which systematically increases with greater anti-stretching of octahedra and Al doping. At higher doping levels (x = 0.20 and 0.50), the films show insulating behavior below room temperature. As the thickness of NdNi0.50Al0.50O3 films varies from 10 nm to 200 nm, the anti-stretching mode got affected, resulting in systematic decrease in resistivity. Our findings confirm that the anti-stretching mode arises by Al doping, and it is associated with the insulating behavior of Al-doped NdNiO3 thin films. © 2025 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.