“…The layered perovskite Ruddlesden–Popper structure (composition: A n +1 B n O 3 n +1 ), a perovskite analogue, consists of a rock salt-type structure (AO) and a perovskite structure (ABO 3 ) where the B site consists of transition metals and n corresponds to the number of perovskite layers. Ruddlesden–Popper layered perovskites have been used as superconductors, − dielectrics, magnetic materials, − ion conductors, − oxygen reduction/generation catalysts, − oxygen storage materials, − and photocatalysts. − Interestingly, these perovskites can be modified by the insertion of H 2 O between the layers to form a structure with the composition A n +1 B n O x ( OH ) y · m H 2 O. − In the synthesis process, layered perovskite oxides are chemically reduced or synthesized to become oxygen-deficient and then placed in air or water vapor to introduce H 2 O between the layers. , Compounds with H 2 O inserted between the layers of this layered perovskite oxide exhibit conductivity with OH – as the carrier. , Water present in the interlayer is desorbed from the interlayer at approximately 100 °C. At temperatures higher than 200 °C, the interlayer protons bound to the oxygen atoms in the perovskite layers are lost and a dehydration reaction occurs. − …”