Journal of the Korean Physical Society, Vol. 62, No. 7, April 2013, pp. 1031∼1034 Enhanced Piezoelectric Properties of Lead-free 0.935(Bi 0.5 Na 0.5 )TiO 3 -0.065BaTiO 3 Thin Films Fabricated by Using Pulsed Laser Deposition J. S. Park, M. H. Lee, D. J. Kim, D. Do, M.-H. Kim, J. S. Kim and T. K. Song ∗ School of Nano & Advanced Materials Engineering, Changwon National University, Changwon 641-773, Korea S. W. Kim, H. I. Choi and K. W. Jang Department of Physics, Changwon National University, Changwon 641-773, Korea I. R. Hwang and B. H. Park Department of Physics, Konkuk University, Seoul 143-701, Korea (Received 8 October 2012, in final form 12 February 2013) 0.935(Bi0.5Na0.5)TiO3-0.065BaTiO3 (BNT-BT) thin films have been grown on Pt(111)/Ti/ SiO2/Si substrates by using a pulsed laser deposition method. Deposition conditions of oxygen pressure and deposition temperature were changed. The BNT-BT thin film deposited at 750 ◦ C and 300 mTorr exhibited a slim hysteresis loop with a remnant polarization (2Pr ) of 11 μC/cm 2 and a low leakage current density of 7.3 × 10 −5 A/cm 2 at 98 kV/cm. The piezoelectric responses of the thin films were investigated using piezoelectric force microscopy with a lock-in amplifier. The thin films exhibited piezoelectric properties with a d 33,f value of 168 pm/V. PACS numbers: 77.65.-j, 77.80.Dj, 77.80.-e Keywords: Lead-free, Piezoelectric, (Bi 0.5 Na 0.5 )TiO 3 -BaTiO 3 , Thin film DOI: 10.3938/jkps.62.1031 I. INTRODUCTION Lead-based piezoelectric ceramics with perovskite structures based on lead zirconate titanate (PZT) are widely used for actuators, sensors, and microelectronic devices because of their excellent piezoelectric properties. However, because of the high toxicity of lead oxide, the use of lead-based ceramics has caused serious lead pollu- tion and environmental problems [1,2]. Therefore, lead- free piezoelectric ceramics must be developed to replace PZT [3–5]. Among several lead-free piezoelectric materi- als (Bi 0.5 Na 0.5 )TiO 3 (BNT) is a promising candidate be- cause of its pronounced ferroelectricity and piezoelectric- ity at room temperature. However, pure BNT materials, large coercive fields and comparatively large conductivity making it difficult to obtain the desired properties. To solve this problem, a variety of doping technique, substi- tution, and solid solution have been developed to fabri- cate materials such as BNT-BaTiO 3 [6–9], BNT-SrTiO 3 [10], BNT-Bi 0.5 K 0.5 TiO 3 [11], BNT-BKT-BT [12], and [Bi 0.5 -(Na 0.7 K 0.2 Li 0.1 ) 0.5 ]TiO 3 [13]. Recently, Sung et al. reported good piezoelectric prop- ∗ E-mail: tksong@changwon.ac.kr erties in (1 - x)(Bi 0.5 Na 0.5 )TiO 3 -xBaTiO 3 ceramics [9]. Among these systems, 0.935(Bi 0.5 Na 0.5 )TiO 3 -0.065Ba- TiO 3 (BNT-BT) ceramics exhibited the best piezoelec- tric properties with d 33 = 146 pC/N at room tempera- ture. Compared to ceramics systems, BNT-BT thin film systems have not been studied yet because they are diffi- cult to deposit due to the volatility of their composition at high temperatures. Because the pulsed laser depo- sition (PLD) method is known to be very suitable for depositing complex oxide materials such as ferroelectrics and piezoelectrics [11–14], in this work, we deposited BNT-BT thin films by using a PLD method and chang- ing the deposition temperature and the oxygen pressure. Piezoelectric responses were measured by using piezo- electric force microscopy. II. EXPERIMENT The BNT-BT oxide target for the PLD method was prepared by using a conventional solid state reaction method with component oxide powders of Bi 2 O 3 (99%), Na 2 CO 3 (99%), TiO 2 (99.9%), and BaCO 3 (99%). They were calcined twice at 780 ◦ C and 800 ◦ C for 2 hours. -1031-