Structural and Ferroelectric Properties of Bi4-xNixTi3O12 Thin Films by Sol-Gel Process
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0966-T07-10
Structural and Ferroelectric Properties of Bi4-xNixTi3O12 Thin Films by Sol-Gel Process Ricardo Melgarejo1, Maharaj S. Tomar2, Rahul Singhal2, and Ram S. Katiyar3 1 Physics, University of Puerto Rico in Cayey, 205, Av. Antonio Barcelo, Cayey, 00736, Puerto Rico 2 Physics, University of Puerto Rico, P.O. Box 9016, Mayaguez, 00680, Puerto Rico 3 Physics, University of Puerto Rico, P.O. Box 23343, San Juan, 00931, Puerto Rico ABSTRACT Nickel-substituted Bi4Ti3O12 (i.e., Bi4-xNixTi3O12) were synthesized by sol-gel process for different compositions. Thin films were deposited on Pt (i.e., Pt/TiO2/SiO2/Si) substrate by spin coating. Materials were characterized by x-ray diffraction and Raman spectroscopy. This study indicates that the material makes a solid solution for the compositions: x = 0.00, 0.05, 0.10, 0.15, 0.20, and 0.30, where a Ni ion replaces the Bi site. The prominent effect of Ni substitution was observed in low-frequency Raman modes. Sol-gel derived thin films of Bi4-xNixTi3O12 on a Pt substrate and post annealed at 700°C were tested for ferroelectric response which showed high remnant polarization (Pr = 22 µC/cm2 for x = 0.15). The leakage current (less then 10-7 A/cm2) at low field was observed in the film with composition x = 0.15 .The polarization of the BNiT (x = 0.15) film decreased to 83% of the initial value after 1x109 switching cycles These results indicate the potential application of Ni substituted bismuth titanate films in non-volatile ferroelectric memories. INTRODUCTION Aurivillius phase family of Bi4-xAxTi3O12 consist of a layer structure of (Bi2O2)2+ and pseudoperovskite [(Bi2-xAxTi3O10)2-] structures stacked along the c-axis direction, where A is a trivalent rare earth element. Chon et al [1] showed that the rotation of TiO6 octahedra in the a-b plane, and the shift of octahedron along the a-axis is largely enhanced by the trivalent A element substitution for Bi in the pseudo perovskite layer. The Bi3+ ion in A site is strongly under bonded and Ti4+ ion is slightly over bonded. As a result, both the Bi2O2 layer and TiO6 tetrahedron are considerably distorted. If Bi ions are partially substituted by trivalent ions in Bi4Ti3O12 near the Ti-O octahedral layers, ferroelectric behavior could be altered as demonstrated by Tomar et al [2] for Bi3.44La0.56Ti3O12 thin films. Although, exact theory based on first principle ab initio calculations for rare earth substituted Bi4Ti3O12 is not known, the origin of large ferroelectric polarization within the layers may be due to the large displacement of Bi3+ cations in the perovskite A site with respect to the chain of TiO6 octahedra. We present here the work on the synthesis, structural characterization, ferroelectric response, dielectric constant and leakage current on Ni substituted Bi4Ti3O12 thin films prepared by sol-gel process and spin coating. EXPERIMENTAL DETAILS Bismuth nitrate, Nickel nitrate, and titanium isopropoxide were used as the precursors for Bi, Ni, and Ti respectively, and acetic acid and methoxy ethanol were the solvent
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