Thermodynamic potential and phase diagram for multiferroic bismuth ferrite (BiFeO₃) （多铁铋铁氧体（BiFeO₃）的热力学势和相图） 
Dmitry V. Karpinsky, Eugene A. Eliseev, Fei Xue, Maxim V. Silibin, Alexandra Franz, Maya D. Glinchuk, Igor O. Troyanchuk, Sergey A. Gavrilov, Venkatraman Gopalan, Long-Qing Chen & Anna N. Morozovska
npj Computational Materials 3, Article number: 19 (2017)
doi:10.1038/s41524-017-0022-2
Published online:10 May 2017
Abstract| Full Text | PDF OPEN

摘要: 本研究构造了纯相和轻微掺杂的铁酸铋的Landau-Ginzburg热力学势与对应相图，铁酸铋在室温下是一种铁电反铁磁体。基于新的X射线和中子衍射实验发展的铁酸铋热力学势补充了目前已有的数据库。本研究证明了一个强大的四阶反铁磁畸变-类型偶（biquadratic antiferrodistortive-type coupling）和作用对定量描述Bi_1-xLa_xFeO₃多铁相图，以及反铁磁、铁电和反铁磁畸变相的温度稳定性至关重要，其也可用来预测新颖中间结构相变。此外，我们的研究显示“旋转磁性的”反铁磁畸变-反铁磁耦合是描述BiFeO₃的R3c相的铁电极化和反铁磁畸变行为的非常重要方法。Landau-Ginzburg热力学势可描述连续和诱发型相变的序列、序参数的温度相关性、以及对外部刺激的相应敏感度。Landau-Ginzburg热力学势若与形状、尺寸和制备方法相关的表面能与能量梯度两个参量结合，则还可以用来预测Bi_1-xLa_xFeO₃薄膜和纳米颗粒的相应铁电和反铁磁畸变性能。

Abstract: We construct a Landau–Ginzburg thermodynamic potential, and the corresponding phase diagram for pristine and slightly doped bismuth ferrite, a ferroelectric antiferromagnet at room temperature. The potential is developed based on new X-ray and neutron diffraction experiments complementing available data. We demonstrate that a strong biquadratic antiferrodistortive-type coupling is the key to a quantitative description of Bi_1−x La _x FeO₃ multiferroic phase diagram including the temperature stability of the antiferromagnetic, ferroelectric, and antiferrodistortive phases, as well as for the prediction of novel intermediate structural phases. Furthermore, we show that “rotomagnetic” antiferrodistortive–antiferromagnetic coupling is very important to describe the ferroelectric polarization and antiferrodistortive tilt behavior in the R3c phase of BiFeO₃. The Landau–Ginzburg thermodynamic potential is able to describe the sequence of serial and trigger-type phase transitions, the temperature-dependent behavior of the order parameters, and the corresponding susceptibilities to external stimuli. It can also be employed to predict the corresponding ferroelectric and antiferrodistortive properties of Bi_1−x La _x FeO₃ thin films and nanoparticles by incorporating the gradient and surface energy terms that are strongly dependent on the shape, size, and preparation method.  

Editorial Summary
Multiferroics: The potential of bismuth ferrite （多铁性材料：铁酸铋的潜力） 

本研究开发了一个理论方法，用来描述具有铁电性铁酸铋的复杂相图。多铁性是材料铁磁性和铁电性等多个性能偶合。铁酸铋或许是室温最佳多铁材料之一 

虽然其在室温多铁性具有多种用途，但其多铁性的基本物理机制仍然不太清楚。由白俄罗斯NAS实用材料科学研究中心和莫斯科电子技术研究所的Dmitry Karpinsky率领的国际研究团队，利用现有的实验数据构建了一种Landau-Ginzbur样热力学势，不仅能定量描述铁酸铋的已知行为，还能预测其新型中间相变结构。 

A theoretical approach for describing the complex phase diagram of the multiferroic bismuth ferrite has been developed. Multiferroics are materials that exhibit multiple types of ferroic ordering, such as ferromagnetism and ferroelectricity, simultaneously. Bismuth ferrite is perhaps one of the best known of these as it exhibits multiferroicity at room temperature, making it useful for a range of applications, but the underlying physical mechanisms responsible for its multiferroic properties remains somewhat unclear. An international team of researchers led by Dmitry Karpinsky from the Scientific-Practical Materials Research Centre of NAS of Belarus and the Moscow Institute of Electronic Technology use existing experimental data to construct a Landau-Ginzbur-like thermodynamic potential that can not only provide a quantitatively description of bismuth ferrites known behavior, but also predicts new intermediate phases.