Microstructural influence on piezoresponse and leakage current behavior of Na 0.5 Bi 0.5 TiO 3 Thin Films
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Microstructural influence on piezoresponse and leakage current behavior of Na0.5Bi0.5TiO3 Thin Films Kumaraswamy Miriyala 1 and Ranjith Ramadurai 1* 1 Department of Materials Science and Metallurgical Engineering, Indian Institute of
Technology Hyderabad, Kandi, Sangareddy, Telangana - 502285, India. Abstract: Sodium bismuth titanate (Na0.5Bi0.5TiO3: NBT) a lead free piezoelectric; exhibits promising features such that it could be an alternate to lead based piezoelectrics. In this work, we report the microstructural influence on piezoelectric and leakage current behavior of NBT thin films grown by pulsed laser ablation (PLD). Various microstructural features like coarse faceted grains and fine spherical grains was achieved by effective optimization of substrate temperature and oxygen partial pressures. The studies reveals that, leakage current of NBT thin films were dominated by interface limited modified Schottky emission type of conduction. The piezoelectric domain studies reveal that for NBT thin films with fine spherical grain the domain pattern was highly dominated by the morphology and in the case of coarse faceted grains the domains were relatively large and the domains were extending beyond the grain boundaries.
INTRODUCTION Sodium bismuth titanate (Na0.5Bi0.5TiO3: NBT) is one of the promising lead free piezoelectric cum ferroelectric compound discovered by Smolenskii in 1961.[1] NBT is a ferroelectric perovskite with heterovalent cations like Na+ and Bi3+occupying the A site.[2] The isoelectronic character of Bi3+ with Pb2+ is considered as a potential alternate to lead based piezoelectric materials.[3] Hence, the structural and electrical properties of NBT and NBT based solid solutions were studied extensively as a plausible replacement for lead based compounds like Pb(Zr,Ti)O3 (PZT).[4, 5] NBT undergoes a sequence of structural phase transitions (on cooling) (i) cubic (Pm3m) to tetragonal (P4bm) phase at 520 °C (ii) tetragonal (P4bm) to rhombohedral (R3c) phase at 200 °C. [6,7] In addition, NBT exhibits a structural heterogeneity with a mixture of rhombohedral and tetragonal symmetries in the temperature range from 200-320 °C. [6, 7] The in-situ temperature dependent transmission electron microscopy studies and structural refinement studies confirm that NBT stabilizes into rhombohedral symmetry at room temperature with polarization direction.[8, 9] However, fabrication of thin films and tuning the property of these materials are essential to meet the current technology needs. Over the past few years, significant work has been carried out in the direction to enhance the piezoelectric properties of NBT thin films. [10,11, 12,13]. In the present study, we have altered the processing conditions to vary the microstructural features of NBT thin films by pulsed laser ablation. Further the correlation between microstructure features and corresponding leakage current density and
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Corresponding Author: Tel. : +91-40-2301 7046 ; E-mail: [email protected]
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