Control of Bond-Strain-Induced Electronic Phase Transitions in Iron Perovskites

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• 作者：Ikuya Yamada ; Hidenobu Etani ; Kazuki Tsuchida ; Shohei Marukawa ; Naoaki Hayashi ; Takateru Kawakami ; Masaichiro Mizumaki ; Kenya Ohgushi ; Yoshihiro Kusano ; Jungeun Kim ; Naruki Tsuji ; Ryoji Takahashi ; Norimasa Nishiyama ; Toru Inoue ; Tetsuo Irifune ; Mikio Takano
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：December 2, 2013
• 年：2013
• 卷：52
• 期：23
• 页码：13751-13761
• 全文大小：578K
• 年卷期：v.52,no.23(December 2, 2013)
• ISSN：1520-510X

文摘

Unusual electronic phase transitions in the A-site ordered perovskites LnCu₃Fe₄O₁₂ (Ln: trivalent lanthanide ion) are investigated. All LnCu₃Fe₄O₁₂ compounds are in identical valence states of Ln³⁺Cu²⁺₃Fe^3.75+₄O₁₂ at high temperature. LnCu₃Fe₄O₁₂ with larger Ln ions (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb) show an intersite charge transfer transition (3Cu²⁺ + 4Fe^3.75+ 鈫?3Cu³⁺ + 4Fe³⁺) in which the transition temperature decreases from 360 to 240 K with decreasing Ln ion size. In contrast, LnCu₃Fe₄O₁₂ with smaller Ln ions (Ln = Dy, Ho, Er, Tm Yb, Lu) transform into a charge-disproportionated (8Fe^3.75+ 鈫?5Fe³⁺ + 3Fe⁵⁺) and charge-ordered phase below 250鈥?60 K. The former series exhibits metal-to-insulator, antiferromagnetic, and isostructural volume expansion transitions simultaneously with intersite charge transfer. The latter shows metal-to-semiconductor, ferrimagnetic, and structural phase transitions simultaneously with charge disproportionation. Bond valence calculation reveals that the metal鈥搊xygen bond strains in these compounds are classified into two types: overbonding or compression stress (underbonding or tensile stress) in the Ln鈥揙 (Fe鈥揙) bond is dominant in the former series, while the opposite stresses or bond strains are found in the latter. Intersite charge transfer transition temperatures are strongly dependent upon the global instability indices that represent the structural instability calculated from the bond valence sum, whereas the charge disproportionation occurs at almost identical temperatures, regardless of the magnitude of structural instability. These findings provide a new aspect of the structure鈥損roperty relationship in transition metal oxides and enable precise control of electronic states by bond strains.