My research is focused on developing Landau-theory description for functional materials and employing phase-field simulations to investigate the evolution of domain structures with and without external stimuli. The systems I have worked on include multiferroic BiFeO3, hexagonal manganites, Ruddlesden-Popper ferroelectrics, PbZrxTi1-xO3, VO2, and polar metals. My main research experiences include the following topics:
Low-energy Domain Walls in Perovskites with Oxygen Octahedral Tilts
A characteristic of the perovskite structure (ABO_3) is the corner-sharing network of the rigid BO_6 oxygen octahedra which can rotate or tilt as a whole (Fig. 1a). The oxygen octahedral tilts are strongly coupled to the microscopic electronic, magnetic, and optical properties. The corresponding domain walls, with distinct physical properties compared to bulk, may potentially be used as new elements for nanoelectronics. In the 2014 Physical Review B paper, I proposed a rotational compatibility condition to identify low-energy domain walls in perovskites with oxygen octahedral tilt instability. It is derived from the strong domain wall energy anisotropy arising from the rigidity and corner-sharing feature of the oxygen octahedral network. As an example, domain walls in multiferroic BiFeO_3 are investigated within the framework of the Ginzburg-Landau-Devonshire theory, where the proposed condition is described by the strong anisotropy of the gradient energy coefficient tensor. The anisotropy of the domain wall energy is shown to be responsible for the unusual ferroelectric domain width and energy in BiFeO_3.
Figure 1. Schematic for low-energy domain walls in perovskites. (a) and (b) Pattern of oxygen octahedral tilts without and with a domain wall. Green and blue diamonds represent oxygen octahedra rotated clockwise and counterclockwise, respectively, with the rotation axis along x3. The balls inside the diamonds represent B atoms. Red and orange balls refer to oxygen and A atoms, respectively. The dot-dashed line in (b) indicate the locations of a domain wall.
Related publications:
1. F. Xue, Y. Gu, L. Liang, Y. Wang, and L.-Q. Chen, “Orientations of low-energy domain walls in perovskites with oxygen octahedral tilts”, Physical Review B 90, 220101(R) (2014)
2. F. Xue, L. Li, J. Britson, Z. Hong, C. A. Heikes, C. Adamo, D. G. Schlom, X. Pan, and L.-Q. Chen, “Switching the curl of polarization vectors by an irrotational electric field”, Physical Review B 94, 100103(R) (2016)
3. L. Li, F. Xue, C. Nelson, A. Melville, C. Heikes, D. Schlom, L.-Q. Chen, and X. Pan, “Size Effect on Spontaneous Flux-closure Domains in BiFeO3 Thin Films”, Microscopy and Microanalysis 22, 1596 (2016)
4. F.-T. Huang, F. Xue, B. Gao, L. Wang, X. Luo, W. Cai, X.-Z. Lu, J. M. Rondinelli, L.-Q. Chen, and S.-W. Cheong, “Domain topology and domain switching kinetics in a hybrid improper ferroelectric”, Nature Communications 7, 11602 (2016)
1. F. Xue, Y. Gu, L. Liang, Y. Wang, and L.-Q. Chen, “Orientations of low-energy domain walls in perovskites with oxygen octahedral tilts”, Physical Review B 90, 220101(R) (2014)
2. F. Xue, L. Li, J. Britson, Z. Hong, C. A. Heikes, C. Adamo, D. G. Schlom, X. Pan, and L.-Q. Chen, “Switching the curl of polarization vectors by an irrotational electric field”, Physical Review B 94, 100103(R) (2016)
3. L. Li, F. Xue, C. Nelson, A. Melville, C. Heikes, D. Schlom, L.-Q. Chen, and X. Pan, “Size Effect on Spontaneous Flux-closure Domains in BiFeO3 Thin Films”, Microscopy and Microanalysis 22, 1596 (2016)
4. F.-T. Huang, F. Xue, B. Gao, L. Wang, X. Luo, W. Cai, X.-Z. Lu, J. M. Rondinelli, L.-Q. Chen, and S.-W. Cheong, “Domain topology and domain switching kinetics in a hybrid improper ferroelectric”, Nature Communications 7, 11602 (2016)