Ruddlesden-Popper phase

Ruddlesden-Popper (RP) phases are a form of layered perovskite structure consist of two-dimensional perovskite slabs interleaved with cations. The general formula of RP phase is A_n-1A’₂B_nX_3n+1, where A, A’, and B are cations, X is an anion and n is the number of the layers of octahedra in the perovskite-like stack.^[1] Generally, it has a phase structure that results from the intergrowth of perovskite-type and NaCl-type structures.

The structure was named after S.N. Ruddlesden and P. Popper, who first synthesized and described the structure in 1957.^[2][3]

The unit cell of Ruddlesden-Popper phase (a)Sr₂RuO₄ (n = 1) and (b)Sr₃Ru₂O₇ (n = 2). The polyhedra represent the perovskite-like structure

Crystal Structure

In the general formula of RP phases, A_n-1A’₂B_nX_3n+1, A and A’ represent alkali, alkaline earth, or rare earth metal while B refers to transition metal. The A cations are located in the perovskite layer and have a 12-fold cuboctahedral coordination to the anions. The A’ cations have a coordination number, CN = 9 and is located at the perovskites boundary with an intermediate block layer. The B cations are located inside the anionic octahedral, pyramids and squares.^[1]

Synthesis

The first series of Ruddlesden-Popper phase, Sr₂TiO₄, Ca₂MnO₄ and SrLaAlO₄ were confirmed by powder X-ray diffraction (PXRD) in 1957.^[2] These compounds were formed by heating up the appropriate oxide or carbonate, in the molecular proportion.

In recent years, interest on perovskite-like structure has been growing and synthetic methods for this compound have been further developed. Alternative to the conventional solid state method, chimie douce or soft chemistry solid-state technique has been utilized to synthesize this class of material. These soft chemistry solid-state techniques include ion-exchange reactions of layered perovskites, ion exchange reactions involving interlayer structural units, topochemical condensation reactions and other techniques such as intercalation-deintercalation reactions and multistep intercalation reactions of layer perovskite.^[4]

Applications

Similar to its parent perovskite structure, Ruddlesden-Popper phases possess interesting properties such as colossal magnetoresistance, superconductivity, ferroelectricity, and catalytic activity.

Ruddlesden-Popper phase LaSr₃FeO₁₀ is an example of layer perovskite that finds its application in the rechargeable metal-air battery.^[5] Due to the layered structure of Ruddlesden-Popper phase, the oxygen that located in between in the layered perovskite is easily removable. The easily removable oxygen is essential to increase the efficiency of Oxygen Evolution Reaction (OER) and Oxygen Reduction Reaction (ORR). In the metal-air battery, OER is a process of charging reaction at the air electrode, while ORR is a process of discharging reaction.

References

1. Beznosikov, B.V.; Aleksandrov, K.S. (2000). "Perovskite-like crystals of the Ruddlesden-Popper series". Crystallography Reports. 45: 792–798. doi:10.1134/1.1312923.
2. Ruddlesden, S.N.; Popper, P. (1958). "The compound Sr₃Ti₂O₇ and its structure". Acta Crystallogr. 11: 54–55. doi:10.1107/S0365110X58000128.
3. Ruddlesden, S.N.; Popper, P. (1957). "New compounds of the K₂NiF₄ type". Acta Crystallogr. 10: 538–539. doi:10.1107/S0365110X57001929.
4. Schaak, R.E.; Mallouk, T.E. (2002). "Perovskites by Design:  A Toolbox of Solid-State Reactions.". Chemistry of Materials. 14: 1455–1471. doi:10.1021/cm010689m.
5. Takeguchi, T.; Yamanaka, T.; Takahashi, H.; Watanabe, H.; Kuroki, T.; Nakanishi, H.; Orikasa, Y.; Uchimoto, Y.; Takano, H.; Ohguri, N.; Matsuda, M.; Murota, T.; Uosaki, K.; Ueda, W. (2013). "Layered Perovskite Oxide: A Reversible Air Electrode for Oxygen Evolution/Reduction in Rechargeable Metal-Air Batteries". Journal of the American Chemical Society. 135: 11125–11130. doi:10.1021/ja403476v.