X-ray Analysis of Strain Relaxed Domain Structure in (100)/(001)-oriented epitaxial FbTiO 3 thick films grown on (100)Sr
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X-ray Analysis of Strain Relaxed Domain Structure in (100)/(001)-oriented epitaxial PbTiO3 thick films grown on (100)SrTiO3 substrates Hiroshi Nakaki1, Yong Kwan Kim1, Shintaro Yokoyama1, Rikyu Ikariyama1, Hiroshi Funakubo1, S. K. Streiffer2, Ken Nishida3, and Keisuke Saito4 1 Department of Innovative and Engineered Material, Tokyo Institute of Technology, Yokohama, 226-8503, Japan 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL, 60439 3 Department of Electric Engineering, National Defence Academy, Yokohama, 239, Japan 4 Application Laboratory, Bruker AXS, Yokohama, 221-0022, Japan ABSTRACT The crystal and domain structures of epitaxially grown (100)/(001)-oriented PbTiO3 films on (100)SrTiO3 substrates with 3.8 µm thickness were investigated by x-ray diffraction (XRD) reciprocal space mapping. The observed poles of the PbTiO3 004, 400, 204, 402 and 420 can be successfully explained using a model with one type of (001) domain and three types of (100) domains. Good agreement is also found between the domain estimation from scanning probe microscopy and that from the in-plane and out-of-plane XRD analysis. INTRODUCTION
x-oriented domains
y-oriented domains
a a c
z-oriented domains
c
a a
c
a a
z, [001]
The domain structure of ferroelectric materials is known to strongly contribute to the ferroelectric and piezoelectric properties. The domain structure of epitaxially grown tetragonal Pb(ZrxTi1-x)O3 films below 400 nm in thickness have been widely investigated over the last 20 years due to ferroelectric memory applications [1, 2]. However, research on films above 500 nm is relatively scarce in spite of the fact that thick PZT films are important for micro-electromechanical system (MEMS) applications [3, 4] that incorporate peizoelectric elements. (100)/(001) oriented epitaxial PbTiO3 films are the most widely investigated for their domain structure. Basically, the domain structure consist of one surface that is nominally (001)oriented domain (z-domain in Figure 1), and the two types of (100)-oriented ones, whose c-axis are aligned but in-plane rotated by approximately 90° from each other (x- and y- domains in Figure 1). Note that coherency across the twin boundaries between domains introduce tilts of several degrees that are not accounted for in the above.
y,
0] 1 [0
x, SrTiO3[100]
Figure 1 Schematic drawing of three types of domains in (100)/(001) oriented epitaxial PbTiO3 films grown on (100)SrTiO3 substrates.
The novel structure labeled as Type III was discovered by our groups for (100)/(001)-oriented epitaxial PbTiO3 films above 1 µm in thickness grown on (100)SrTiO3 substrates [5]. The three dimensional domain alignment was analyzed by piezoelectric force microscopy (PFM) in conjunction with in-plane and out-of-plane X-ray diffraction analysis [6]. This reveals the existence of the fully strain-relaxed structure as shown in Figure 2. The domain structure consist of one kind of (001)-oriented domain, c-domain (c domain in Figure 2), and three kinds of (100)-orie
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