Thermal-strain driving sharp metal-to-insulate transition and island-grain growth of solution-derived NdNiO3 epitaxial thin films

An ultra-sharp metal-to-insulate transition (MIT) of 1.24 K − 1 in the epitaxial perovskite NdNiO 3 thin films was derived by the chemical solution deposition on the LaAlO 3 substrates. The thermal strains from shrink, grain growth, and thermal expansion coefficient misfit play a key role in the film microstructure and electrical properties. The originally theoretical in-plane compressive epitaxial strain changes into a tensile one caused by the thermal driving force. It relaxes with improved grain growth via decreased oxygen vacancies with increasing annealing temperature, while the concurrently enhanced tensile strain from the thermal expansion coefficient misfit between the films and the substrate leads to the destabilization of Ni 3 + and the higher MIT temperature. Nevertheless, too much higher tensile strain gives rise to island-grain growth in the films, leading to the weak and even disappeared MIT.