Multifunctional Polycrystalline Ferroelectric Materials Processing a
This book presents selected topics on processing and properties of ferroelectric materials that are currently the focus of attention in scientific and technical research. Ferro-piezoelectric ceramics are key materials in devices for many applications, suc
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VOL. 50, NO. 2
April 2012
Structure of BaTi1−x Fex O3−δ Multiferroics Using X-ray Analysis N. V. Dang,1, 2, ∗ Ha M. Nguyen,1, 3, † Pei-Yu Chuang,3 T. D. Thanh,1 V. D. Lam,1 Chih-Hao Lee,3, 4, ‡ and L. V. Hong1, § 1
Institute of Materials Science, Vietnam Academy of Science and Technology, Hanoi, Vietnam 2 Faculty of Physics, College of Science, Thai Nguyen University, Thai Nguyen, Vietnam 3 Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan 4 National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (Received September 8, 2011) BaTiO3−δ (BTO) and BaTi0.88 Fe0.12 O3−δ (BTFO) polycrystalline samples were investigated to understand the role that Fe dopant and oxygen vacancy play on their various properties. Their structures were examined using X-ray diffraction and X-ray absorption spectroscopy. Their optical and conduction properties were also characterized at room temperature. Our results show that BTO is a tetragonal-phase ferroelectric material with a wide band gap Eg ≈ 3.51 eV while BTFO is a hexagonal-phase multiferroic material with smaller band gap Eg ≈ 3.40 eV. Fe doping ions, which exist in both Fe3+ and Fe4+ forms, give rise to positively-charged oxygen vacancies to create donor impurity levels in the forbidden band. The UV-VIS absorption spectrum of BTFO exhibits a broadening in the visible region. The red shift is observed in both the absorption and photoluminescence spectra relative to those of BTO. The leakage current is larger in BTFO than in BTO. PACS numbers: 75.85.+t, 78.70.Dm, 61.05.cp
I. INTRODUCTION
Since its discovery in 1945, barium titanate, BaTiO3 (BTO), has attracted a great deal of attention from both fundamental research and a variety of dielectrics/electro-mechanics and nonlinear optics applications [1–3]. This fact is due to its high dielectric constant and low dielectric loss; good piezoelectric, pyroelectric, and ferroelectric properties [1–3]; positive temperature coefficient [4, 5]; excellent photorefractive crystals for self-pumped phase conjugation [6], four-wave mixing [7], and many other photorefractive processes [8]; thin film’s electro-optic modulation to frequencies over 40 GHz [9]; etc. Moreover, BTO doped with transition metals (e.g., Mn, Co, and Fe) has been recently revealed to exhibit the so-called giant electro-strain effect [10–12]. For example, Fe-doped BTO single crystals showed a quite large strain of 0.75% at 200 V/mm, which is 40 times larger than that of ∗
Electronic Electronic ‡ Electronic § Electronic
†
address: address: address: address:
[email protected] [email protected] [email protected] [email protected]
http://PSROC.phys.ntu.edu.tw/cjp
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c 2012 THE PHYSICAL SOCIETY
OF THE REPUBLIC OF CHINA
VOL. 50
N. V. DANG, HA M. NGUYEN, et al.
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conventional Pb(Zr,Ti)O3 at the same electric field, and about 10 times larger than that of the high electro-strained Pb(Zn1/3 Nb2/3 )O3 -PbTiO3 single crystals [11]. This effect is based on a new mechanism related to point defects, i
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