Unlocking zeolite-like structures as a new family of interstitial oxide ion conductors: insights into carrier trapping, collective local distortion, and correlated disorder

Abstract

Zeolites have emerged as indispensable materials for applications ranging from catalysis and separation to adsorption and ion exchange, owing to their uniquely ordered porous architectures composed of well-defined channels and cavities. Inspired by the promising oxygen defect tolerance observed in various open structural frameworks, herein, we have developed a new zeolite-like feldspar structure, A2B2C2O8 with 4- and 8-membered rings, in the case of Sr1−xLaxGa2Ge2O8+0.5x, as a new family of interstitial oxide ion conductors due to its open structural framework for accommodating and transporting interstitial oxide ions. Average structural analysis revealed that the interstitial oxygen occupies the centers of 4-membered rings, existing in a coordination equilibrium quasi-free state that confers high mobility; however, this contrasts with the experimentally observed low mobility. Local structural analysis further revealed that the local collective distortions in GaO4 and GeO4 tetrahedra, together with the correlated disorder of interstitial oxygen coordinated with Ge, hidden within the average structure, are critical to interstitial oxygen mobility from the 4-membered ring to the 8-membered ring. Our findings demonstrate zeolite-like structures as a new family of interstitial oxide ion conductors, offering new insights into the intricate interplay between oxide ion mobility, collective distortions, and correlated disorder at the local scale.