First-Principles Study of Intrinsic Point Defects and Optical Properties of SmNiO₃

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 Sm_Ni antisite defects, while Ni_Sm 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.