Correlation Between Ferroelectric and Fluorescent Properties by Introducing Eu Atoms Into Strontium Bismuth Tantalate Fi
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1111-D07-06
Correlation between Ferroelectric and Fluorescent Properties by introducing Eu Atoms into Strontium Bismuth Tantalate Films Koji Aizawa1 and Yusuke Ohtani2 1 Optoelectronic Device System Research and Development Center, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa 921-8501, Japan 2 Graduate School of Electrical Engineering and Electronics, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa 921-8501, Japan ABSTRACT Electrical and fluorescent properties of Sr-deficient strontium bismuth tantalate co-doped with excess-Bi and Eu atoms (BiEu-SBT) were investigated, in which the Eu/Bi ratio was changed between 0 and 0.1. BiEu-SBT were synthesized on Pt (200 nm)/Ti (50 nm)/SiO2/Si substrates by using Sr0.8Bi2.2Ta2O9 and Sr0.8(Bi2, Eu0.2)Ta2O9 mixed precursor solutions with a concentration of 0.33 mol/kg, in which Sr concentration was fixed at 0.8. From X-ray diffraction analysis, the diffraction peaks from Aurivillius phases were observed in the synthesized BiEuSBT as well as in pure SBT. In BiEu-SBT, the lattice parameters along a- and c-axes at the Eu/Bi ratio of 0.1 in comparison with those of 0 decreased approximately 0.27 and 0.19 %, respectively. The remnant polarization (2Pr) values of the synthesized BiEu-SBT with Eu/Bi ratio of 0 and 0.1 were approximately 8.4 and 6.8 µC/cm2, respectively. From photoluminescence (PL) measurement at a wavelength of 615 nm as a function of Eu/Bi ratio, the PL intensity of the synthesized BiEu-SBT was proportional to the Eu/Bi ratio, whereas, the 2Pr values were slightly decreased by Eu-doping. INTRODUCTION Ferroelectric oxide films have great interests in the application to high-density nonvolatile ferroelectric random access memories [1]. Particularly, the layered-structure perovskite ferroelectric oxides such as SrBi2Ta2O9 (SBT) and (Bi,La)4Ti3O12 have a excellent fatigue-free properties [2,3]. Recently, the electro-optic effects of ferroelectric SBT films have been investigated [4]. Therefore, Ln3+-doped SBT films have also attracted much attention as a promising candidate for optoelectronic applications such as optical amplifier and modulator because of the luminescence of Ln3+. SBT is known as an Aurivillius compound with a general formula of (Bi2O2)2+(SrTa2O7)2and its structure consists of Bi2O2 layers and double TaO6 octahedra with a Sr-site [7,8] In Srdeficient and Bi-excess SBT (Sr0.8Bi2.2Ta2O9), the Bi substitution at the Sr-site has occurred the larger spontaneous polarization caused by the structural distortion of TaO6 octahedra [9, 10]. Therefore, it is known that the substitution of ionic radius ion smaller than that of Bi ion to the Sr-site is effective for improving the ferroelectric properties. In the several rare-earth ions, the effective ionic radius of Eu3+ is 0.138 nm for 12-coordination and this value is smaller than that of Bi3+ (0.145 nm for 12-coordination) [11, 12]. We have first reported the Eu3+-doped SBT (Eu-SBT) films with both ferroelectric and fluorescent properties [5, 6]. Eu-SBT films have showed
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