Long-Range Lattice Matching between (100)/(010) Bismuth-Layered Perovskite Structure and (101) Rutile Structure
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Long-Range Lattice Matching between (100)/(010) Bismuth-Layered Perovskite Structure and (101) Rutile Structure Takayuki Watanabe, Keisuke Saito1, Minoru Osada2, Toshimasa Suzuki3, Masayuki Fujimoto3, Mamoru Yoshimoto4, Atsushi Sasaki4, Jin Liu4, Masato Kakihana4 and Hiroshi Funakubo Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan 1 Application Laboratory, XRD Section, Analytical Department, PANalytical Japan, 35-1 Sagamiono 7-chome, Sagamihara-shi, Kanagawa 228-0803, Japan 2 PRESTO, Japan Science and Technology Corporation (JST), 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan 3 Physical Properties Evaluation Center, Central R&D Laboratories, TAIYO YUDEN Co., Ltd., 5607-2 Nakamuroda, Haruna-machi, Gunma 370-3347, Japan 4 Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan ABSTRACT a-/b-axis-oriented epitaxial bismuth layer-structured ferroelectric thin films were epitaxially grown on (101)-oriented oxide with rutile structure. The long-range lattice matching between the ferroelectric layer and the bottom rutile layer, particularly the number of rutile units facing one ferroelectric unit and the surface orientation, were discussed for (100)(010)Bi4Ti3O12//(101)TiO2 structure. Cross sectional transmission electron microscope analysis suggests that seven rutile units lie under one a-/b-axis-oriented Bi4Ti3O12 unit with lower misfit dislocation density comparing to eight rutile units by one Bi4Ti3O12 model. Based on this result, the surface orientation at the interface was simulated to give us an appropriate ion alignment model. The titanium layer in the (101)TiO2 structure is most likely to match with the oxygen layer in the a-/b-axis-oriented Bi4Ti3O12 film.
INTRODUCTION Bismuth layer-structured ferroelectrics (BLSFs) including SrBi2Ta2O9, (Bi3.25La0.75)Ti3O12 and (Bi3.5Nd0.5)Ti3O12 have been investigated for ferroelectric random access memory (FeRAM) application because of their fatigue-free nature [1-3]. Up to now, fabrications of films with their spontaneous polarization vector normal to substrates have been investigated for the largest switching charge [4,5]. For this purpose, the long c-axis should then align parallel to the film surface, because the spontaneous polarization vector of the BLSFs is lying along the a-axis. Recently, we reported a-/b-axis-oriented epitaxial growth of SrBi2Ta2O9 (SBT) and Bi4Ti3O12 (BIT) films with long-range lattice matching on rutile-structured materials such as TiO2, RuO2 and IrO2 with (101) orientation [4,6]. These approaches provided a direct study of ferroelectric property along the spontaneous polarization vector, i.e., parallel direction to the stacking of pseudoperovskite and (Bi2O2)2+ layers. To understand heteroepitaxial growth mechanisms, mismatch calculation and structural similarity of closely packing ion are macroscopically important. On the other hand, the information of atomic alignment at the interfac
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