Enhanced Spontaneous Polarization of Dysprosium-substituted Lead Zirconate Titanate Thin Films by a Chemical Solution De
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Enhanced Spontaneous Polarization of Dysprosium-substituted Lead Zirconate Titanate Thin Films by a Chemical Solution Deposition Method Hiroshi Uchida1, Hiroshi Nakaki1, Shoji Okamoto2, Shintaro Yokoyama2, Hiroshi Funakubo2 and Seiichiro Koda1 1 Department of Chemistry, Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo, 102-8554, Japan 2 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8502, Japan
ABSTRACT Influences of the B-site substitution using Dy3+ ion on the crystal structure and ferroelectric properties of lead zirconate titanate (PZT) films were investigated. Dy3+-substituted PZT films with nominal chemical compositions of Pb1.00Dyx(Zr0.40Ti0.60)1-(3x/4)O3 (x = 0 ~ 0.06) were fabricated by a chemical solution deposition (CSD). Polycrystalline PZT films with preferential orientation of (111)PZT were obtained on (111)Pt/TiO2/SiO2/(100)Si substrates, while epitaxially-grown (111)PZT films were fabricated on (111)SrRuO3//(111)Pt//(100)YSZ//(100)Si substrate. Ratio of PZT lattice parameters (c/a), which corresponds to its crystal anisotropy, was enhanced by the Dy3+-substitution with x = 0.02. Spontaneous polarization (Ps) of Dy3+-substituted PZT film (x = 0.02) along polar [001] axis of PZT lattice was estimated from saturation polarization (Psat) value of the epitaxially-grown (111)PZT film on (111)SrRuO3//(111)Pt//(100)YSZ//(100)Si to be 84 µC/cm2 that was significantly larger than that of non-substituted PZT (= 71 µC/cm2). We concluded that the enhancement of Ps value could be achieved by the Dy3+-substitution that promoted the crystal anisotropy of PZT lattice.
INTRODUCTION Lead zirconate titanate [Pb(Zr,Ti)O3; PZT] has excellent ferroelectric properties, i.e., large polarization and small coercive electric field, etc, that are suitable for the component material of nonvolatile random access memory (NvRAM), microelectromechanical system (MEMS), electro-optic devices, etc. Many ion-doping techniques for PZT films were attempted in recent studies in order to improve the ferroelectric properties because these properties affect on the performance of electronic devices mentioned above significantly. However, enhancement of the spontaneous polarization (Ps) of PZT films based on the ion-substitution has never been achieved so far due to lack of the material-design concept as for the PZT films, whereas some researchers revealed that its ferroelectric properties could be improved by ion-substitution based on the site-engineering concepts as for other materials such as Pb-free bismuth layer structured ferroelectrics like strontium bismuth tantalate (SrBi2Ta2O9; SBT) [1,2] and bismuth titanate (Bi4Ti3O12; BIT) [3-6]. For example, Tominaga et al. reported that A-site substitution such as La3+-substituted PZT films degraded the remanent polarization (Pr) of PZT film as well as the coercive field (Ec) because it lowers the crystal anisotropy, i.e., the c/a ratio of PZT lattice [7,8]. Also, B-site subs
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