Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.
Nat Mater. 2010 Mar;9(3):253-8. doi: 10.1038/nmat2632. Epub 2010 Feb 14.
Hexagonal YMnO(3) shows a unique improper ferroelectricity induced by structural trimerization. Extensive research on this system is primarily due to its candidacy for ferroelectric memory as well as the intriguing coexistence of ferroelectricity and magnetism. Despite this research, the true ferroelectric domain structure and its relationship with structural domains have never been revealed. Using transmission electron microscopy and conductive atomic force microscopy, we observed an intriguing conductive 'cloverleaf' pattern of six domains emerging from one point--all distinctly characterized by polarization orientation and structural antiphase relationships. In addition, we discovered that the ferroelectric domain walls and structural antiphase boundaries are mutually locked and this strong locking results in incomplete poling even when large electric fields are applied. Furthermore, the locked walls are found to be insulating, which seems consistent with the surprising result that the ferroelectric state is more conducting than the paraelectric state. These fascinating results reveal the rich physics of the hexagonal system with a truly semiconducting bandgap where structural trimerization, ferroelectricity, magnetism and charge conduction are intricately coupled.
六方 YMnO(3) 由于结构三聚化而呈现出独特的失配位向铁电性。对该体系的广泛研究主要归因于其作为铁电存储器的候选材料以及铁电性和磁性的有趣共存。尽管进行了这些研究，但铁电畴结构及其与结构畴的关系从未被揭示过。使用透射电子显微镜和导电原子力显微镜，我们观察到从一点出现的六个畴的有趣的导电“三叶形”图案——所有畴都通过极化方向和结构反相关系明显地进行了特征化。此外，我们发现铁电畴壁和结构反相畴界是相互锁定的，这种强锁定导致即使施加大电场也无法完成极化。此外，发现锁定的畴壁是绝缘的，这似乎与令人惊讶的结果一致，即铁电态比顺电态更具导电性。这些引人入胜的结果揭示了六角体系的丰富物理特性，其中具有真正的半导体带隙，结构三聚化、铁电性、磁性和电荷传导紧密耦合。
