The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adom.201900958. 2−y 2 , d z 2 ) levels. [35] The splitting of the d-orbital was successfully explained by the crystal field theory. The ground state properties of these materials are mainly governed by the two interactions; i) the electron correlations (U) and, ii) SOC (λ) in the crystal field split narrow bands. [36] Among d electron systems, electrons in 3d TMOs experiences large electron correlations due to localized nature of 3d orbitals. The idea of electron-electron interaction was given by Sir N. F. Mott in 1949. It originated from the fact that the NiO was expected to be a metal according to the band theory, while the experiments showed insulating behavior. [37][38][39][40][41] This disagreement of experiments with the theory was explained by Hubbard who attributed the insulating state to the splitting

The extreme sensitivity of the metal–insulator (M–I) transition in RNiO3 (R = rare-earth ion) nickelates to various extrinsic and intrinsic factors rely on mechanisms driving structure–property relations. Here, we demonstrate a unique way to control the M–I transition of epitaxial Pr0.5Sm0.5NiO3 thin films using a mosaic template of the LaAlO3(100) substrate; two sets of epitaxial films were deposited on highly oriented crystals and mosaic (with multiple crystallites) crystals. While the former films exhibit a robust and sharp M–I transition, the films on the mosaic substrate show distinctively much more subtle and broad transition, albeit same factors suggesting compositional purity. Terahertz (THz) dynamic conductivity too behaves very differently for the two types of films; Drude dynamics dominate the conductivity of highly crystalline films, whereas disorder-driven Drude–Smith conductivity prevails in mosaic films. Using this mosaic structure-controlled M–I transition and conductivity dynamics, we propose to implement these two templates of films for digital and analog THz transmission amplitude modulators.

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Understanding the dynamics of phase-transitions, interpretations of their experimental observations and their agreement with theoretical predictions continue to be a long-standing research interest. Here, we present detailed phase-transition dynamics of rare earth nickelates associated with its first-order metal-insulator transition. The thermal hysteresis shows absence of training effect and defies the Preisach model. A large phase-coexistence in insulating state during cooling suggests kinetically arrested glassy dynamics of the phase-transition. Experimentally derived hysteresis scaling exponent is much larger than the mean-field predicted universal value of 2/3. In the phase-coexistence region, the quench and hold measurement depicts higher stability of the metallic state compare to that of the insulating one; highlighting the manifestation of phase-coexistence via asymmetric spinodal decomposition. All these observations for nickelates are in stark contrast to the phase-transition dynamics of canonically similar vanadates but are closer to those of glasses, alloys. A substantial disagreement between the experiment and theory emphasizes the necessity to incorporate system-dependent details for the accurate interpretation of the experimental results.