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Rare earth nickelates (RNOs) have been extensively studied in recent decades because of the metal–insulator phase transition, which can be driven by chemical doping. In the present study, we apply the first-principles calculation to investigate the electronic structures, optical properties, and migration behaviors of Li-doped RNO. Results show that when the doping ratio reaches 100%, RNO changes from the metallic state into an insulating state, which is confirmed by the experimental report. Regarding the optical properties, the absorption coefficient and reflectivity decrease in Li-doped RNO over the entire range of visible and infrared light compared with pristine systems. The migration of Li along the [001] direction of RNO is studied and shows that as the radius of rare earth atoms decreases, the migration barrier generally shows a gradually decreasing trend. These findings may shed light on the application of RNO in electrochromic devices.

Defects are closely related to the optical properties and metal-to-insulator phase transition in SmNiO3 (SNO) and therefore play an important role in their applications. In this paper, the intrinsic point defects were studied in both stoichiometric and nonstoichiometric SNO by first-principles calculations. In stoichiometric SNO, the Schottky defects composed of nominally charged Sm, Ni, and O vacancies are the most stable existence. In nonstoichiometric SNO, excess Sm2O3 (or Sm) creates the formation of O vacancies and Ni vacancies and SmNi antisite defects, while NiSm antisite defects form in an excess Ni2O3 (or Ni and NiO) environment. Oxygen vacancies affect electronic structures by introducing additional electrons, leading to the formation of an occupied Ni–O state in SNO. Moreover, the calculations of optical properties show that the O vacancies increase the transmittance in the visible light region, while the Ni interstitials decrease transmittance within visible light and infrared light regions. This work provides a coherent picture of native point defects and optical properties in SNO, which have implications for the current experimental work on rare-earth nickelates compounds.