Ferroelectric and piezoelectric properties of lead-free BaTiO 3 doped Bi 0.5 Na 0.5 TiO 3 thin films from metal-organic solution deposition Susant Kumar Acharya a,b , Sang-Kwon Lee b , Jung-Hwan Hyung b , Yun-Ho Yang a , Bok-Hee Kim a , Byung-Guk Ahn a,⇑ a Division of Advanced Materials Engineering, Hydrogen and Fuel Cell Research Center, Chonbuk National University, Jeonju 561–756, Republic of Korea b Department of Semiconductor Science and Technology, Basic Research Laboratory (BRL), Semiconductor Physics Research Center (SPRC), Chonbuk National University, Jeonju 561–756, Republic of Korea article info Article history: Received 16 April 2012 Received in revised form 14 June 2012 Accepted 14 June 2012 Available online 23 June 2012 Keywords: Thin films Piezoelectricity Dielectric response Ferroelectrics abstract Lead-free 0.94Bi 0.5 Na 0.5 TiO 3 –0.06BaTiO 3 (BNT–BT) piezoelectric thin films were prepared by metal- organic solution deposition onto a Pt/Ti/SiO 2 /Si substrate. A dense and well crystallized thin film with a perovskite phase was obtained by annealing these films at 700 °C. Atomic force microscopy showed that these films were smooth and crack-free with an average grain size on the order of 200 nm. Thin films of 356 nm thickness exhibited a small signal dielectric constant and a loss tangent at 1 kHz of 613 and 0.044, respectively. Ferroelectric hysteresis measurements indicated a remanent polarization value of 21.5 lC/cm 2 with a coercive field of 164.5 kV/cm. The leakage current density of the thin film was 4.08  10 4 A/cm 2 at an applied electric field of 200 kV/cm. A typical butterfly-shaped piezoresponse loop was observed and the effective piezoelectric coefficient (d 33 ) of the BNT–BT thin film was approxi- mately 51.6 pm/V. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The most widely used piezoelectric materials in electronic de- vices (such as sensors, actuators and memory) are Pb(Zr,Ti)O 3 (PZT) ceramics, owing to their exceptional piezoelectric properties [1]. These materials have some shortcomings, however, including imprint problems, lead toxicity, and especially fatigue when cycled over 10 7 times [2]. All of these deficits serve to limit the applica- tions of PZT ceramics. Recently, lead-free piezoelectric materials have been attracting a great deal of attention as alternatives to PZT [3–5]. Among these materials, bismuth sodium titanate (Bi 0.5- Na 0.5 TiO 3 (BNT)) has been seen as a promising candidate for use in lead-free piezoelectric ceramics due to its pronounced ferroelec- tricity (P r = 38 lC/cm 2 ) at room temperature and its relatively high Curie point (T c = 320 °C) [6,7]. This ceramic also has deficiencies, including high conductivity and a large coercive field, which can cause problems in the poling process. These problems may be mitigated, however, by forming solid solutions of BNT with a variety of other compounds including BaTiO 3 [8],K 0.5 Bi 0.5 TiO 3 [9,10], Na 0.5 K 0.5 NbO 3 [11] and BiFeO 3 [12]. Among these solid solu- tions, there is significant interest in the (Bi 0.5 Na 0.5 ) 1x Ba x TiO 3 (BNT–BT) system owing to the morphotropic phase boundary (MPB) formed between its respective end members: the rhombo- hedral Bi 0.5 Na 0.5 TiO 3 and the tetragonal BaTiO 3 perovskites [13– 15]. This solid solution in its bulk form exhibits good dielectric (rel- ative dielectric constant at room temperature of K‘ 1200 and maximum values of K‘ 7000), ferroelectric (remanent polariza- tion of P r 45 lC/cm 2 and coercive field of E c 35 kV/cm), and pie- zoelectric (d 33 110 pC/N) properties in the MPB composition [16]. In addition, recent studies on BNT–BT materials have shown that large electromechanical strains can be induced under high electric fields at MPB compositions [17,18]. These properties make this lead-free material extremely attractive for applications in electronics. Piezoelectric materials, especially in the form of thin films, offer a number of advantages when used in micro electromechanical systems (MEMS). These advantages are related to the large mo- tions which can be generated in these films (often with low hyster- esis) and their high available energy densities, as well as their high sensitivity coupled with wide dynamic ranges and low power requirements [19]. The integration of BNT–BT into thin films there- fore is very attractive, due to potential applications in microelec- tronic devices with optimum electrostrictive or piezoelectric actuation [20]. Despite this potential usefulness, there is currently very little literature concerning BNT–BT thin films, especially with regard to the study of their piezoelectric properties. Publications that do exist concern BNT–BT thin films which have been prepared by chemical solution deposition [16,20], pulse laser deposition [21–23], RF magnetron sputtering [24], metal organic 0925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2012.06.071 ⇑ Corresponding author. Tel.: +82 10 3085 2300; fax: +82 63 270 2386. E-mail address: bkahn@jbnu.ac.kr (B.-G. Ahn). Journal of Alloys and Compounds 540 (2012) 204–209 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom