Order–Disorder Transition Involving the A-Site Cations in Ln3+Mn3V4O12 Perovskites

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• 作者：Yuichi Shimakawa ; Shoubao Zhang ; Takashi Saito ; Michael W. Lufaso ; Patrick M. Woodward
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：January 6, 2014
• 年：2014
• 卷：53
• 期：1
• 页码：594-599
• 全文大小：331K
• ISSN：1520-510X

文摘

A crossover from the A-site-ordered double-perovskite structure with Im3̅ 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 Gd³⁺) 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 Ln³⁺Mn²⁺₃V^3.75+₄O₁₂. Compounds with small Ln³⁺ ions like Y³⁺ and Lu³⁺, on the other hand, crystallize with the Pnma simple-perovskite structure with chemical composition (Ln³⁺_1/4Mn²⁺_3/4)V^3.75+O₃, where the Ln³⁺ and Mn²⁺ ions are disordered at the A site. The random distribution of the small A-site cation induces the a^{鈥?/sup>b+a鈥?/sup> 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 LnMn₃V₄O₁₂ is thus a result of the structural stability due to the cooperative tilting of the VO₆ octahedra. The Mn2+ ions at the A鈥?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鈥揹isorder 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.}