Ruddlesden-Popper phases were first synthesised by Ruddlesden and Popper in 1958 . The structure consists of nABO3 perovskite layers which are sandwiched between two AO rocksalt layers . The lower-order (n=1) phases such as La2NiO4+ (LNO) and Pr2NiO4+ (PNO) have been studied extensively . The main motivation for intense research focus on the n = 1 Ruddlesden-Popper phase materials stemmed from their superior capability of storing a substantial amount of interstitial oxygen in their structure which bestowed the materials with significant oxide ion conductivity, thereby rendering the materials mixed ionic-electronic conductors (MIEC) at intermediate temperatures .