Shimakawa, Yuichi Zhang, Shoubao Saito, Takashi Lufaso, Michael W. Woodward, Patrick M. Order–Disorder Transition Involving the A‑Site Cations in <i><i>Ln</i></i><sup>3+</sup>Mn<sub>3</sub>V<sub>4</sub>O<sub>12</sub> Perovskites A crossover from the A-site-ordered double-perovskite structure with <i>Im</i>3̅ cubic symmetry to the simple-perovskite structure with <i>Pnma</i> orthorhombic symmetry is found in <i><i>Ln</i></i>Mn<sub>3</sub>V<sub>4</sub>O<sub>12</sub> (<i><i>Ln</i></i> = La, Nd, Gd, Y, Lu) synthesized under high-pressure conditions. Relatively large <i><i>Ln</i></i><sup>3+</sup> ions (La<sup>3+</sup>, Nd<sup>3+</sup>, and Gd<sup>3+</sup>) induce the <i>a</i><sup>+</sup><i>a</i><sup>+</sup><i>a</i><sup>+</sup> in-phase cooperative tilting of the VO<sub>6</sub> octahedra, resulting in the A-site-ordered double-perovskite structure with chemical composition <i>Ln</i><sup>3+</sup>Mn<sup>2+</sup><sub>3</sub>V<sup>3.75+</sup><sub>4</sub>O<sub>12</sub>. Compounds with small <i>Ln</i><sup>3+</sup> ions like Y<sup>3+</sup> and Lu<sup>3+</sup>, on the other hand, crystallize with the <i>Pnma</i> simple-perovskite structure with chemical composition (<i>Ln</i><sup>3+</sup><sub>1/4</sub>Mn<sup>2+</sup><sub>3/4</sub>)­V<sup>3.75+</sup>O<sub>3</sub>, where the <i>Ln</i><sup>3+</sup> and Mn<sup>2+</sup> ions are disordered at the A site. The random distribution of the small A-site cation induces the <i>a</i><sup>–</sup><i>b</i><sup>+</sup><i>a</i><sup>–</sup> tilting distortion of the VO<sub>6</sub> 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 <i>Ln</i>Mn<sub>3</sub>V<sub>4</sub>O<sub>12</sub> is thus a result of the structural stability due to the cooperative tilting of the VO<sub>6</sub> octahedra. The Mn<sup>2+</sup> ions at the A′(A) site contribute local magnetic moments, whereas the V<sup>3.75+</sup> ions at the B site play a role in metallic conduction. The observed magnetic behaviors are consistent with the order–disorder distribution of the Mn<sup>2+</sup> ions at the A site, antiferromagnetism in the A-site-ordered double perovskites, and magnetic spin glass in the A-site-disordered simple perovskites. VO 6 octahedra;LnMn 3V;site;ion 2014-01-06
    https://acs.figshare.com/articles/journal_contribution/Order_Disorder_Transition_Involving_the_A_Site_Cations_in_i_i_Ln_i_i_sup_3_sup_Mn_sub_3_sub_V_sub_4_sub_O_sub_12_sub_Perovskites/2335852
10.1021/ic402740k.s001