Elsevier

Journal of Alloys and Compounds

Volume 586, 15 February 2014, Pages 549-554
Journal of Alloys and Compounds

Ferroelectric and piezoelectric properties of lead-free Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BaTiO3-thin films near the morphotropic phase boundary

https://doi.org/10.1016/j.jallcom.2013.10.028Get rights and content

Highlights

  • Lead-free Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BaTiO3 piezoelectric thin films with compositions near morphotropic phase boundary were grown on Pt/Ti/SiO2/Si (1 0 0) substrates using metal-organic solution method.

  • All BNT–BKT–BT films have a single phase perovskite structure with no pyrochlore phases.

  • 0.884BNT–0.036BT–0.08BKT thin film (n = 2) has the best surface morphology compared with other films.

Abstract

Lead-free Bi0.5Na0.5TiO3 (BNT)–Bi0.5K0.5TiO3 (BKT)–BaTiO3 (BT) piezoelectric thin films with compositions near the morphotropic phase boundary (MPB) were deposited by metal-organic solution deposition on Pt/Ti/SiO2/Si (1 0 0) substrates. The compositional dependences of their microstructure and ferroelectric/piezoelectric properties were investigated. The results indicated that all the thin films have a single-phase perovskite structure and show outstanding electrical properties at room temperature. We found that the thin film with a composition of 0.884BNT–0.08BKT–0.036BT showed the best structural and electrical properties, with a dielectric constant, remnant polarization, and effective piezoelectric constant of ∼638, ∼27 μC/cm2 and ∼79 pC/N, respectively. We suggest that these superior properties are due to this sample’s high degree of alignment of ferroelectric domains in the MPB region and largest grain size.

Introduction

It is well-known that Pb(Zr,Ti)O3 (PZT) materials play a dominant role in piezoelectric devices, such as sensors, actuators and transducers. However, it has been noted that waste products containing lead (Pb) cause critical environmental problems. Moreover, the high volatility of toxic lead fumes during processing makes PZT compounds dangerous to handle. To resolve these problems, considerable attention has been directed toward the development of lead-free ferroelectric materials [1]. Among several lead-free piezoelectric materials, bismuth sodium titanate (Bi0.5Na0.5TiO3, BNT) is intensively studied as an alternative to its lead-based counterparts because it exhibits a large remnant polarization (Pr = 38 μC/cm2) and a relatively high Curie temperature (Tc = 320 °C) [2], [3], [4]. A morphotropic phase boundary (MPB) is known to play a very important role in piezoelectric ceramics such as PZT materials in which both rhombohedral (FR) and tetragonal (FT) ferroelectric phases exist simultaneously [5]. Because more possible polarization variants are available, the dielectric, ferroelectric, and piezoelectric properties are enhanced at MPB compositions [6]. BNT material has an FR perovskite structure (R3c) below its Tc [7]. A number of materials possessing the tetragonal (FT) phase, such as BaTiO3 (BT) and Bi0.5K0.5TiO3 (BKT) (P4 mm), have been added to BNT ceramics to create MPB compositions [8], [9], [10]. In BNT–BT and BNT–BKT systems the MPB composition reportedly exists in the range of 0.6−0.7 mol BT and 0.16–0.20 mol BKT, respectively, providing relatively high piezoelectric and dielectric properties [10], [11], [12], [13]. Accordingly, the use of a multi-component system (i.e., BNT–BKT–BT) is effective for further increasing the electrochemical properties. To date, the BNT–BKT–BT system has been extensively explored in bulk form [6], [14], [15], [16], [17]. Although the achievement of enhanced electrochemical behaviors in bulk materials is promising, many of the ultimate applications of these systems, such as a microelectromechanical system (MEMS) device, require 2D thin films. Compared to their ceramic counterparts, the growth and the characterization of BNT-based thin films are still at an infancy stage, but substantial progress has been made in improving the electrochemical properties of BNT-based thin films in the last two years [18], [19], [20]. Various deposition techniques such as chemical solution deposition [21], [22], sol–gel spin coating [23], [24], metal organic solution deposition [25], and pulse laser deposition [26], [27], are employed to achieve high quality BNT-based thin films. Besides various fabrication techniques utilized, various dopants such as Mn [20], [28], [29], Li [30], Ce and Fe [31], and La and Ce [32] have been used to further improve the electrical properties. Furthermore, La0.7Ca0.3MnO3 (LCMO) [18] and SrTiO3 [33] as seeding layers have also been used to obtain highly oriented BNT-based thin films for improving the electrical properties of the thin films. However, the BNT–BKT–BT ternary system has yet to be explored extensively. For the BNT–BKT–BT thin film system, Abazari et al. reported 88BNT–8BKT–4BT epitaxial thin films synthesized through pulsed laser deposition (PLD) on SrRuO3-coated SrTiO3 substrates [34]. They showed a saturated polarization hysteresis loop with a large Pr = 30 μC/cm2. More recently, Jeon et al. deposited polycrystalline BNT–BKT–BT thin films on SiO2/Ti/Pt substrates through a chemical solution deposition method and obtained superior results compared with the bulk materials [35]. The MPB region in the BNT–BKT–BT system can be determined using the four points P1, P2, P3, and P4, as shown schematically in Fig. 1 [6], [14], [36]. Recently, Zhang et al. suggested that the BNT–BKT–BT triple phase system within the MPB region gives superior results compared to those along the MPB line [6].

In this work, thin films with six compositions, along a red line combining 0.94BNT–0.06BT (P1) and 0.80BNT–0.20BKT (P3), as depicted in Fig. 1, were deposited on Pt/Ti/SiO2/Si substrates by using a metal-organic solution deposition method. These compositions can be described as (0.94–0.028n)BNT–(0.06–0.012n)BT–0.04nBKT, where n = 0, 1, 2, 3, 4, and 5. For n = 0 and n = 5, they are 0.94BNT–0.06BT and 0.80BNT–0.20BKT, respectively. The phase composition, microstructure, and dielectric and ferroelectric properties of these crystalline thin films were investigated and analyzed in detail.

Section snippets

Experimental details

Barium acetate [Ba(CH3COO)2], bismuth nitrate [Bi(NO3)3·5H2O], sodium acetate (NaOOCCH3), potassium–nitrate (KNO3), and titanium isopropoxide (Ti[OCH(CH3)2]4) were used as starting materials, and acetyl acetone, isopropyl alcohol, distilled water, and acetic acid were used as solvents. Diethanolamine [HN(CH2CH2OH)2] was selected as ligands. The detailed solution preparation was reported previously [25], [30]. The stock solutions were spin-coated onto Pt/Ti/SiO2/Si (1 0 0) substrates at a spin

Results and discussion

Fig. 2 shows XRD patterns of the BNT–BKT–BT thin films with different compositions; they reveal a pure perovskite structure with no pyrochlore phases. These structures can be explained as follows. First, as the BNT-based thin films nucleate from the amorphous phase and then grow during annealing, they pass through an intermediate pyrochlore phase and are partly changed into a perovskite structure if the annealing temperature is not sufficiently high [37]. On the other hand, the entire

Conclusions

Thin films with compositions of (0.94–0.028n) BNT–(0.06–0.012n) BT–0.04nBKT (n = 0, 1, 2, 3, 4, and 5) near the MPB were deposited on Pt/Ti/SiO2/Si substrates through using metal-organic solution deposition. All the samples had a pure perovskite structure without any impurity phase. All the thin films showed excellent composition dependent electrical properties at room temperature. The film corresponding to n = 2 exhibited optimal electrical properties, with a dielectric constant, remnant

Acknowledgments

This work was supported by the Fusion Research Program for Green Technologies through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant No. 2010-0019097). This paper was also supported by research funds of Chonbuk National Universtiy in 2013. This work was partially supported by a grant from the Global Excellent Technology Innovation R&D Program, funded by the Ministry of Knowledge Economy, Republic of Korea (10038702-2010-01).

References (47)

  • X.-C. Zheng et al.

    Thin Solid Films

    (2012)
  • P. Du et al.

    J. Alloys Comp.

    (2013)
  • F. Ni et al.

    J. Alloys Comp.

    (2012)
  • M.R. Soares et al.

    J. Eur. Ceram. Soc.

    (2000)
  • S.-T. Zhang et al.

    Acta Mater.

    (2012)
  • M. Cernea et al.

    Curr. Appl. Phys.

    (2012)
  • W.-J. Ji et al.

    Ceram. Int.

    (2012)
  • L. Luo et al.

    J. Alloys Comp.

    (2012)
  • M. Rawat et al.

    Ceram. Int.

    (2013)
  • Z. Yang et al.

    Mater. Res. Bull.

    (2008)
  • A. Hussain et al.

    J. Alloys Comp.

    (2013)
  • C.C. Jin et al.

    J. Alloys Comp.

    (2013)
  • C. Jin et al.

    Appl. Surf. Sci.

    (2013)
  • M. Cernea et al.

    J. Alloys Comp.

    (2012)
  • M. Cernea et al.

    J. Eur. Ceram. Soc.

    (2012)
  • S.K. Acharya et al.

    J. Alloys Comp.

    (2012)
  • W. Sakamoto et al.

    Sens. Actuator. A-Phys.

    (2013)
  • W. Li et al.

    J. Alloys Comp.

    (2013)
  • Y.H. Jeon et al.

    Mater. Lett.

    (2013)
  • J.-F. Trelcat et al.

    Ceram. Int.

    (2012)
  • C.H. Yang et al.

    Mater. Lett.

    (2012)
  • Y.-L. Huang et al.

    Surf. Coat. Technol.

    (2013)
  • A.Z. Simões et al.

    Mater. Chem. Phys.

    (2008)
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