Order-disorder transition involving the A-site cations in Ln 3+Mn3V4O12 perovskites
A crossover from the A-site-ordered double-perovskite structure with Im3̄ cubic symmetry to the simple-perovskite structure with Pnma orthorhombic symmetry is found in LnMn3V4O12 (Ln = La, Nd, Gd, Y, Lu) synthesized under high-pressure conditions. Relatively large Ln3+ ions (La3+, Nd3+, and Gd 3+) induce the a+a+a+ in-phase cooperative tilting of the VO6 octahedra, resulting in the A-site-ordered double-perovskite structure with chemical composition Ln 3+Mn2+3V3.75+4O 12. Compounds with small Ln3+ ions like Y3+ and Lu3+, on the other hand, crystallize with the Pnma simple-perovskite structure with chemical composition (Ln3+1/4Mn 2+3/4)V3.75+O3, where the Ln 3+ and Mn2+ ions are disordered at the A site. The random distribution of the small A-site cation induces the a-b +a- tilting distortion of the VO6 octahedra. The observed phase crossover is well explained by the structural stability calculation based on the bond-valence-sum model, and the most stable crystal structure gives the smallest unit-cell volume. This A-site-cation size-dependent phase transition between the A-site-ordered double-perovskite and A-site-disordered simple-perovskite structures in LnMn3V 4O12 is thus a result of the structural stability due to the cooperative tilting of the VO6 octahedra. The Mn2+ ions at the A′(A) site contribute local magnetic moments, whereas the V3.75+ ions at the B site play a role in metallic conduction. The observed magnetic behaviors are consistent with the order-disorder distribution of the Mn2+ ions at the A site, antiferromagnetism in the A-site-ordered double perovskites, and magnetic spin glass in the A-site-disordered simple perovskites. © 2013 American Chemical Society.
Digital Object Identifier (DOI)
Shimakawa, Zhang, S., Saito, T., Lufaso, M. W., & Woodward, P. M. (2014). Order–Disorder Transition Involving the A‑Site Cations in Ln 3+Mn3V4O12 Perovskites. Inorganic Chemistry, 53(1), 594–599. https://doi.org/10.1021/ic402740k