Structural percolation evolution throughout the metal-to-insulator transition in NdNiO3

This work presents the structural phase percolation during the entire temperature range of metallic-to-insulating phase transition (MIT) in a high quality NdNiO₃ thin film deposited onto (001)-oriented LaAlO₃ substrate. The results show the correlation between the symmetry breaking oxygen-breathing distortion and the occurrence of the MIT. From Raman scattering experiments, the monoclinic and orthorhombic phases' coexistence was fully characterized, and their volume fractions determined as a function of temperature. At the critical threshold of the insulating domain percolation, the monoclinic volume fraction attains the predicted 2/3 for a three-dimensional lattice, evidencing a structural percolative process. The experimental results here reported give a more general insight into percolative phenomena in NdNiO₃ thin films.