Tan Qiuhong, Wang Qianjin, Liu Yingkai
College of Physics and Electronic Information, Yunnan Normal University, Kunming 650500, China.
Yunnan Provincial Key Laboratory for Photoelectric Information Technology, Yunnan Normal University, Kunming 650500, China.
Materials (Basel). 2018 Jun 11;11(6):985. doi: 10.3390/ma11060985.
Multiferroic materials have been receiving attention for their potential applications in multifunctional devices. Chemical substitution is an effective method for improving the physical properties of BiFeO₃ (BFO). However, different experimental results have been reported for Lanthanum- (La-) and Manganese (Mn) -doped BFO ceramics. Here, we systematically studied the magnetic properties and spontaneous polarization of La-, Mn-, and Nitrogen (N) -doped tetragonal BiFeO₃ using density functional theory with the generalized gradient approximation and U-value method. The calculated results demonstrated that the systems show ferromagnetism with Mn and N doping, whereas no magnetization was found with La doping in G- and C-type antiferromagnetic orderings. Our research further revealed that the ferromagnetism is attributed to the - orbital hybridization. Berry-phase polarization calculations predicted a large polarization of 149.2 µC/cm² along the [001] direction of pure tetragonal BFO. We found that La and N substitution had little influence on the spontaneous polarization, whereas Mn substitution reduced the spontaneous polarization. The reduced energy barrier heights of the doped systems indicate the reduced stability of the off-centering ferroelectricity against the thermal agitation. These findings provide greater understanding for controlling and tuning the multiferroic properties of BFO.
多铁性材料因其在多功能器件中的潜在应用而受到关注。化学取代是改善BiFeO₃（BFO）物理性能的有效方法。然而，关于镧（La）和锰（Mn）掺杂的BFO陶瓷，已有不同的实验结果报道。在此，我们采用广义梯度近似和U值方法的密度泛函理论，系统地研究了La、Mn和氮（N）掺杂的四方相BiFeO₃的磁性和自发极化。计算结果表明，Mn和N掺杂的体系呈现铁磁性，而在G型和C型反铁磁序中，La掺杂未发现磁化现象。我们的研究进一步表明，铁磁性归因于 - 轨道杂化。贝里相极化计算预测，纯四方相BFO沿[001]方向的极化强度为149.2 μC/cm²。我们发现，La和N取代对自发极化影响较小，而Mn取代则降低了自发极化。掺杂体系的能垒高度降低表明，偏离中心的铁电性相对于热扰动的稳定性降低。这些发现为控制和调节BFO的多铁性特性提供了更深入的理解。
