Possible Ferroelectricity in SnTiO3 by First-Principles Calculations
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Possible Ferroelectricity in SnTiO3 by First-Principles Calculations Yoshinori Konishi1, Michio Ohsawa1, Yoshiyuki Yonezawa1, Yoshiya Tanimura2, Toyohiro Chikyow3,4, Toshiyuki Wakisaka4, H. Koinuma4, Akira Miyamoto5, Momoji Kubo5, and Katsumi Sasata5 1
Fuji Electric Corporate Research and Development, Ltd., Yokosuka 240-0194, Japan KCM Corporation, Minato-ku, Nagoya, 455-8668, Japan 3National Institute for Materials Science, Tsukuba, 305-0047, Japan 4Material and Structures laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan 5Department of Materials Chemistry, Tohoku University, Sendai 980-8579, Japan 2
ABSTRACT The prospect of lattice structure and ferroelectricity of SnTiO3 have been studied by first-principles calculations within local density approximation. The results showed that the SnTiO3 has the minimum total energy within almost tetragonal perovskite structure of a=b=3.80
, c=4.09 . The calculated electronic structure of SnTiO resembles that of PbTiO because the Ti 3d states, Sn 5s and 5p states hybridize with the O 2p orbitals. The moment of spontaneous polarization of SnTiO was estimated as 73 C/cm , which is as large as that of PbTiO . 3
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INTRODUCTION Perovskite type ferroelectric materials containing lead (such as lead titanate (PbTiO3), lead zirconate titanate (Pb(Zr,Ti)O3) are widely used in electronic apparatuses such as capacitors and piezoelectric applications utilizing perovskite’s high ferroelectric behavior. From an environmental viewpoint, we want to stop using lead compounds. Thus, lead-free ferroelectric materials have been studied. Among them, compounds possessing a bismuth layer structure (such as Bi4Ti3O12, SrBi2Ta2O9) are considered to be the most practical. However bismuth is also detrimental to one’s health. Consequently, we must investigate ferroelectric materials that are not only lead-free but also bismuth-free. In this paper, we propose a lead-free and bismuth-free ferroelectric material that is expected to have high ferroelectricity comparable with PbTiO3. The origin of ferroelectricity has been theoretically studied by first principles calculations[1-5]. Ferroelectricity emerges when the ionic molecular has double the minimum potential of its spatial position. The long-range Coulomb energy favors ferroelectric distortions. But, the short-range repulsion between the ions tends to eliminate the distortions. Cohen[2] discussed about PbTiO3 and BaTiO3 that they have similar cohesive properties but have different ferroelectric behaviors.
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He calculated all electron energy of PbTiO3 and BaTiO3 by means of local density approximation (LDA) method. He clamed that the covalent bond between the Ti ions and O ions weakens the repulsive potential and restores the double-well structure. He calculated that the Pb 6s and O 2p states are strongly hybridized in PbTiO3, but Ba 5p does not hybridize with the valence state, leading in directly to change in the Ti-O interactions. Miyazawa et al.[5] pointed out that the Pb 6p also hybridize with the
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