Metal‐to‐insulator transition and stability for metastable correlated perovskite nickelates with complex <i>RE</i> ‐composition

Abstract Among the family of materials showing metal‐to‐insulator transition (MIT), the correlated perovskite nickelates ( RE NiO 3 ) exhibit the most widely tunable critical temperature ( T MIT ) that is useful in applications, such as critical temperature resistive thermistors, thermochromics, and infrared camouflage. Although the continuity in adjusting T MIT is enabled via introducing multiple RE within RE NiO 3 , the resultant impact on their functional and thermodynamic stabilities owing to the complication in RE ‐compositions yet remain unclear. Herein, we demonstrate the electronic MIT properties and decomposition routes for nickelates with complex RE ‐compositions, covering a large variety of combinations among the light ( RE L ), middle ( RE M ), and heavy ( RE H ) RE ‐compositions. Although the T MIT varies monotonically with the average ionic RE radius ( r RE ) within RE NiO 3 , their resultant resistive switches are reduced when enlarging either the mixing entropy or the difference in r RE . Despite exhibiting multiple RE ‐compositions, the decomposition routes are in general similar to the RE NiO 3 exhibiting single RE ‐compositions: their respective partial RE M or RE H tends to be decomposed directly into RE 2 O 3, while the RE L decomposed into layered perovskites. Also, their decomposition temperature descends with the reduction in their average r RE , while extra energy beyond the thermodynamic equilibrium is required to trigger their decomposition.