S.N. Ruddlesden and P. Popper reported a new class of materials with the overall formula of An+1BnO3n+1, in 1958 . The structure consists of nABO3 perovskite layers alternating between two AO rock-salt layers and the number of perovskite polyhedral units packed between rock-salt units of the structure decides the phase of the material (Figure ) . Since the perovskite structure allow accommodating oxygen defects and Ruddlesden-Popper (RP) phases contain perovskite layer/s in their structure, it is one of the reasons behind the expectation that these materials could work as promising oxygen conductors.