近年來由於薄膜磊晶技術的發展，顯示一種有別以往的形態相邊界，在此邊界常是超過一個相存在。而在室溫下關於多鐵材料鐵酸鉍BiFeO3 的研究中指出，當薄膜受到來自基板的壓縮應力時，會因此經歷由應變所以引起的相轉換，由原本接近菱長晶結構轉成類似立方晶的單斜晶晶相。
在本研究中，為了了解薄膜在此邊界上形成的中間狀態，我們深度探討混相鐵酸鉍薄膜的電域結構。藉著旋轉樣品，透過壓電力顯微鏡的掃描，並使掃描方向相對晶軸特定角度。我們發現至少存在兩種相，其平行膜面的電極化分別指向[100]與 [110]。
電域擁有相異電極化指向的形成原因是因至少兩種的單斜晶，其晶格結構的自發性形變方向不同。這些電域結構的形成不僅是為了使靜電能降到最低以滿足靜電的邊界條件。同時，形變的方向亦要使接面上原子位移造成的彈性能降到最低。
鐵酸鉍在相邊界上的多相共存這些穩定態彼此能量差異不大，因此一點變化就能衍伸相當多新穎的物理特性，如本樣品中的高壓電特性，值得更深度的討論

Recent advances in thin-film technology shows a new type of morphotropic phase boundary driven by substrate strain. It had been reported that the compressive stress on the BiFeO3 (BFO) multiferroic films resulted in a strain-induced phase transformation from rhombohedrally- (R-like) to
tetragonally- (T-like) distorted monoclinic pervoskite.
In this study, to reveal the intermediate states on the particular phase boundary, we investigated the intrinsic domain structures of mixed-phase BFO films. As rotating the sample being scanned along the principle crystallographic directions, piezoresponse force microscopy (PFM) showed the coexistence of at least two phases with in-plane polarization pointing along [100] and [110].
These differences in the orientation of domains are due to the spontaneous deformation of two monoclinic phases. Likewise, the domain structures form to fulfill not only minimizing the ferroelectric energy on the inter-plane but also satisfying the electrostatic boundary condition. Meanwhile the direction of the lattice deformation is considered to decrease the elastic energy on the interface.
These stable phases coexist under tiny difference of free energy. Hence, if there is any little parameter at variance, it will induce peculiar properties such like high piezoelectric coefficient of this film. It’s worth to have more investigation about this issue.

1 H. Sawada and K. Terakura, Physical Review B 58 (11), 6831 (1998).
2 D. Khomskii, Physics 2, 20 (2009).
3 Y. Tokura, J. Magn. Magn. Mater. 310 (2007).
4 Bas B. Van Aken, Jean-Pierre Rivera, Hans Schmid, and Manfred Fiebig, Nature 449 (7163), 702 (2007).
5 Y. Yang, J. M. Liu, H. B. Huang, W. Q. Zou, P. Bao, and Z. G. Liu, Physical Review B 70 (13), 132101 (2004).
6 Bas B. Van Aken, Thomas T. M. Palstra, Alessio Filippetti, and Nicola A. Spaldin, Nat Mater 3 (3), 164 (2004).
7 D. I. Khomskii, ChemInform 38 (4), no (2007).
8 Dzyaloshirskii, Nonmetals. Sov Phys JETP 19, 12 (1964).
9 T. Moriya, ocirc, and ru, Physical Review 120 (1), 91 (1960).
10 N. A. Spaldin and M. Fiebig, Science 309 (5733), 391 (2005).
11 W. Eerenstein, N. D. Mathur, and J. F. Scott, Nature 442 (7104), 759 (2006).
12 T. Zhao, A. Scholl, F. Zavaliche, K. Lee, M. Barry, A. Doran, M. P. Cruz, Y. H. Chu, C. Ederer, N. A. Spaldin, R. R. Das, D. M. Kim, S. H. Baek, C. B. Eom, and R. Ramesh, Nat Mater 5 (10), 823 (2006).
13 R. Ramesh and Nicola A. Spaldin, Nat Mater 6 (1), 21 (2007).
14 F. Kubel and H. Schmid, Acta Crystallographica Section B-Structural Science 46, 698 (1990).
15 F. Zavaliche, P. Shafer, R. Ramesh, M. P. Cruz, R. R. Das, D. M. Kim, and C. B. Eom, Applied Physics Letters 87 (25), 2149180 (2005).
16 S. K. Streiffer, C. B. Parker, A. E. Romanov, M. J. Lefevre, L. Zhao, J. S. Speck, W. Pompe, C. M. Foster, and G. R. Bai, Journal of Applied Physics 83 (5), 2742 (1998).
17 A. L. Roitburd, physica status solidi (a) 37 (1), 329 (1976).
18 M. Davis, D. Damjanovic, and N. Setter, Physical Review B 73 (1), 014115 (2006).
19 Huaxiang Fu and Ronald E. Cohen, Nature 403 (6767), 281 (2000).
20 B. Noheda, D. E. Cox, G. Shirane, R. Guo, B. Jones, and L. E. Cross, Physical Review B 63 (1), 014103 (2000).
21 David Vanderbilt and Morrel H. Cohen, Physical Review B 63 (9), 094108 (2001).
22 I. A. Kornev, L. Bellaiche, P. E. Janolin, B. Dkhil, and E. Suard, Physical Review Letters 97 (15), 157601 (2006).
23 H. M. Christen, J. H. Nam, H. S. Kim, A. J. Hatt, and N. A. Spaldin, Physical Review B 83 (14), 144107 (2011).
24 H. Bea, B. Dupe, S. Fusil, R. Mattana, E. Jacquet, B. Warot-Fonrose, F. Wilhelm, A. Rogalev, S. Petit, V. Cros, A. Anane, F. Petroff, K. Bouzehouane, G. Geneste, B. Dkhil, S. Lisenkov, I. Ponomareva, L. Bellaiche, M. Bibes, and A. Barthelemy, Physical Review Letters 102 (21), 217603 (2009).
25 A. J. Hatt, N. A. Spaldin, and C. Ederer, Physical Review B 81 (5), 054109 (2010).
26 C. Ederer and N. A. Spaldin, Physical Review Letters 95 (25), 257601 (2005).
27 M. N. Iliev, M. V. Abrashev, D. Mazumdar, V. Shelke, and A. Gupta, Physical Review B 82 (1), 5 (2010).
28 R. J. Zeches, M. D. Rossell, J. X. Zhang, A. J. Hatt, Q. He, C. H. Yang, A. Kumar, C. H. Wang, A. Melville, C. Adamo, G. Sheng, Y. H. Chu, J. F. Ihlefeld, R. Erni, C. Ederer, V. Gopalan, L. Q. Chen, D. G. Schlom, N. A. Spaldin, L. W. Martin, and R. Ramesh, Science 326 (5955), 977 (2009).
29 L. W. Martin, Y. H. Chu, M. B. Holcomb, M. Huijben, P. Yu, S. J. Han, D. Lee, S. X. Wang, and R. Ramesh, Nano Letters 8 (7), 2050 (2008).
30 D. Mazumdar, V. Shelke, M. Iliev, S. Jesse, A. Kumar, S. V. Kalinin, A. P. Baddorf, and A. Gupta, Nano Letters 10 (7), 2555 (2010).
31 Zuhuang Chen, Zhenlin Luo, Chuanwei Huang, Yajun Qi, Ping Yang, Lu You, Chuansheng Hu, Tom Wu, Junling Wang, Chen Gao, Thirumany Sritharan, and Lang Chen, Advanced Functional Materials 21 (1), 133 (2011).
32 Z. H. Chen, L. You, C. W. Huang, Y. J. Qi, J. L. Wang, T. Sritharan, and L. Chen, Applied Physics Letters 96 (25), 252903 (2010).
33 C. Ederer and N. A. Spaldin, Physical Review B 71 (6), 060401 (2005).
34 I. A. Kornev and L. Bellaiche, Physical Review B 79 (10), 100105 (2009).
35 S. Lisenkov, D. Rahmedov, and L. Bellaiche, Physical Review Letters 103 (4), 047204 (2009).
36 S. Prosandeev Zuhuang Chen, Z. L. Luo, Wei Ren, Yajun Qi, C. W. Huang, Lu You, C. Gao, I. A. Kornev, Tom Wu, Junling Wang, P. Yang, T. Sritharan, L. Bellaiche, Lang Chen, arXiv:1104.4712.
37 H. Y. Kuo, Y. C. Shu, H. Z. Chen, C. J. Hsueh, C. H. Wang, and Y. H. Chu, Journal of the European Ceramic Society In Press, Corrected Proof.
38 Multimode manual.
39 Sch, ouml, Kristin A. nau, Ljubomira A. Schmitt, Michael Knapp, Hartmut Fuess, R. Eichel, uuml, A. diger, Hans Kungl, and Michael J. Hoffmann, Physical Review B 75 (18), 184117 (2007).
40 B. Noheda, D. E. Cox, G. Shirane, J. A. Gonzalo, L. E. Cross, and S. E. Park, Applied Physics Letters 74 (14), 2059 (1999).
41 Z. H. Chen, Z. L. Luo, Y. J. Qi, P. Yang, S. X. Wu, C. W. Huang, T. Wu, J. L. Wang, C. Gao, T. Sritharan, and L. Chen, Applied Physics Letters 97 (24), 242903 (2010).
42 Q. He, Y. H. Chu, J. T. Heron, S. Y. Yang, W. I. Liang, C. Y. Kuo, H. J. Lin, P. Yu, C. W. Liang, R. J. Zeches, W. C. Kuo, J. Y. Juang, C. T. Chen, E. Arenholz, A. Scholl, and R. Ramesh, Nat. Commun. 2 (2011).