Structure of BaTi1−x FexO3−δ Multiferroics Using X-ray Analysis

CHINESE JOURNAL OF PHYSICS VOL. 50, NO. 2 April 2012

Structure of BaTi1−xFexO3−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

2Faculty of Physics, College of Science,

Thai Nguyen University, Thai Nguyen, Vietnam

3Department of Engineering and System Science,

National Tsing Hua University, Hsinchu 30013, Taiwan

4National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan

(Received September 8, 2011)

BaTiO3−δ (BTO) and BaTi0.88Fe0.12O3−δ (BTFO) polycrystalline samples were inves￾tigated 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 tem￾perature. 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 address: [email protected]

†Electronic address: [email protected]

‡Electronic address: [email protected]

§Electronic address: [email protected]

http://PSROC.phys.ntu.edu.tw/cjp 262 c 2012 THE PHYSICAL SOCIETY

OF THE REPUBLIC OF CHINA