High-Pressure Synthesis of A-Site Ordered Double Perovskite CaMnTi2O6 and Ferroelectricity Driven by Coupling of A-Site Ordering and the Second-Order Jahn鈥揟eller Ef

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• 作者：Akihisa Aimi ; Daisuke Mori ; Ko-ichi Hiraki ; Toshihiro Takahashi ; Yue Jin Shan ; Yuichi Shirako ; Jianshi Zhou ; Yoshiyuki Inaguma
• 刊名：Chemistry of Materials
• 出版年：2014
• 出版时间：April 22, 2014
• 年：2014
• 卷：26
• 期：8
• 页码：2601-2608
• 全文大小：431K
• 年卷期：v.26,no.8(April 22, 2014)
• ISSN：1520-5002

文摘

We successfully synthesized a novel ferroelectric A-site-ordered double perovskite CaMnTi₂O₆ under high-pressure and investigated its structure, ferroelectric, magnetic and dielectric properties, and high-temperature phase transition behavior. Optical second harmonic generation signal, by frequency doubling 1064 nm radiation to 532 nm, was observed and its efficiency is about 9 times as much as that of SiO₂ (伪-quartz). This compound possesses a tetragonal polar structure with space group P4₂mc. P-E hysteresis measurement demonstrated that CaMnTi₂O₆ is also ferroelectric. A spontaneous polarization calculated by use of point charge model and the observed remnant polarization are 24 and 3.5 渭C/cm², respectively. CaMnTi₂O₆ undergoes a ferroelectric鈥損araelectric order鈥揹isorder-type phase transition at 630 K. The structural analysis implies that both the ordering of shift of Mn²⁺ from the square-planar and the off-center displacement of Ti⁴⁺ in TiO₆ octahedra are responsible for ferroelectricity. CaMnTi₂O₆ belongs to a new class of ferroelectrics in which A-site ordering and second-order Jahn鈥揟eller distortion are cooperatively coupled. The finding gave us a new concept for the design of ferroelectric materials.