(583am) Fundamental Insights On the Oxygen Transport Mechanisms in K2NiF4-Structure Materials

Oxygen transport materials are of significant importance to a number of relevant technological applications including energy generation systems (i.e. solid oxide fuel cell, electrolyzers), and oxygen transport membranes. We focus on a very promising class of fast oxygen ion transport materials known as K₂NiF₄-structure oxides. These oxide materials have a layered structure that can be described as alternating layers of perovskite and rocksalt structures, where oxygen anions can diffuse via the vacancy and interstitial migration mechanisms, respectively. In K₂NiF₄-structure oxides, the vacancies existing in the perovskite-like layers facilitate an oxygen migration along the a-b plane, while the rocksalt layers accommodate a significant oxygen excess charge-compensated by the formation of electron holes in the perovskite layers. We have employed quantum chemical calculations in combination with experimental techniques to study and determine the geometric and electronic characteristic of K₂NiF₄-structure materials that lead to the highest oxygen exchange rates. We will discuss the factors that govern the energetics of Frenkel defects and direct oxygen diffusion mechanisms in these materials. Oxygen transport processes, which involve oxygen vacancies migration along c axis and in a-b plane as well as interstitial oxygen migration, will be evaluated by first-principle density functional theory (DFT) approaches. We will discuss the most likely oxygen migration pathway mediated by either oxygen deficiency or oxygen excess in these materials as a function of their composition.