In the last two decades, structure and properties of Ruddlesden–Popper phase (RP) A₂BO₄ oxides with K₂NiF₄ structure, have been widely investigated. But to the best of our knowledge, no review article is available in the literature on recent studies on these oxides. Therefore, in this article, recent studies on structure, electrical, dielectric, and optical properties of these oxides have been reviewed. Special attention is put on to highlight the effect of doping and oxygen stoichiometry on the structure and properties of these oxides. Further, important applications of these oxides have also been mentioned in this article.

Phase pure powders of SrCeO₃ and Sr₂CeO₄ have been synthesized by calcination at 1000 ℃ for 14 h via solid state ceramic route. Ceramics/pellets of these samples have been obtained by sintering at 1200 ℃ for 12 h. The Rietveld refinement of X-ray diffraction (XRD) pattern of sintered powders confirmed orthorhombic structure of both the samples with space group Pnma and Pbam for SrCeO₃ and Sr₂CeO₄, respectively. Scanning electron microscopic (SEM) studies indicated that both the compounds have dense microstructure, but morphology and size of the grains are different. The impedance spectroscopy technique has been employed to study the relaxation phenomenon. DC conductivity of the samples has been measured in the temperature range of 200-600 ℃ to understand the conduction mechanism. The activation energy for relaxation (E_relax) and DC conduction (E_cond) are found to be the same for both the compounds. Based on the numerical value of activation energies, relaxation and conduction mechanism in both the samples are attributed to migration of doubly ionized oxygen vacancies (V_o^••). Photoluminescence technique has been employed to confirm the existence of oxygen vacancies. These studies have indicated that migration of oxygen vacancies in Sr₂CeO₄ is occurring mainly along a and c direction, i.e., via perovskite cells. Further, the present work has clearly indicated that besides optical properties, electrical properties of Sr₂CeO₄ are also interesting and can be utilized for various applications such as oxide ion conduction electrolyte in solid oxide fuel cells (SOFCs).