The role of structural distortions in triggering the metal to insulator transition in NdNiO3

Abstract The role of the structural distortions on the metal to insulator transition (MIT) of NdNiO3 is still a controversial topic. NdNiO3 ceramic, 260 nm and 110 nm thin films deposited onto (001)-oriented LaAlO3 substrates were studied to unravel the effect of structural symmetry breaking on the electronic phase transition. Resistivity measurements evidence the coexistence of metallic and insulating states below the TMI, while magnetization measurements confirm the expected TMI = TN for all samples. The structural symmetry was investigated across the MIT, through Raman scattering spectroscopy, with the orthorhombic Pnma phase being found at high temperatures, but the emergence of the monoclinic P21/n phase only occurring well below TMI, which is an unexpected experimental result since the structural transition has been understood as a necessary trigger for the MIT. These experimental results, which are noticeably independent of the sample type/quality, imply a temperature difference between the structural and electronic/magnetic ordering, thus contrasting with current theoretical models.