Impact of Crystalline Orientation on the Switching Field in Barium Titanate Using Piezoresponse Force Spectroscopy
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Impact of Crystalline Orientation on the Switching Field in Barium Titanate Using Piezoresponse Force Spectroscopy 1 Nikhil K. Ponon , Daniel J. R. Appleby1, Erhan Arac1, Kelvin S. K. Kwa1, Jonathan P. Goss1, Ullrich Hannemann2, Peter K. Petrov2, Neil M. Alford2 and Anthony O’Neill1 1
School of Electrical and Electronic Engineering, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom 2
Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, United Kingdom ABSTRACT Understanding crystal orientation at the ferroelectric domain level, using a non destructive technique, is crucial for the design and characterization of nano-scale devices. In this study, piezoresponse force spectroscopy (PFS) is used to identify ferroelectric domain orientation. The impact of crystal orientation on the switching field of ferroelectric BaTiO3 is also investigated at the domain level. The preferential domain orientations for BaTiO3 thin films prepared by pulsed laser deposition (PLD) in this study are [001], [101] and [111]. They have been mapped onto PFS spectra to show three corresponding switching fields of 460, 330 and 120 kV/cm respectively. In addition, the electric field at which the enhanced piezoresponse occurs was found to vary, due to a phase change. The polarization reversal occurs via a 2-step process (rotation and switching) for [101] and [111] orientations. The piezoresponse enhancement is absent for the [001] (pure switching) domains. The results demonstrate that an electric field induced phase change causes the [101] and [111] domains to reverse polarization at a lower field than the [001] domain. INTRODUCTION The multitude of applications that piezoresponse force microscopy (PFM) can offer have revolutionized nano-scale domain studies of ferroelectric materials recently [1]. Tip induced polarization switching has greatly improved the resolution of domain imaging and spectroscopy. Piezoresponse force spectroscopy (PFS) is a static spectroscopic mode which is based on the detection of local inverse piezoelectric deformations of domains by an external electric field induced by an atomic force microscopy (AFM) tip. A detailed description of PFS technique is given elsewhere [2]. Previous experimental studies have shown that ferroelectric materials like BaTiO3 exhibit an enhanced piezoresponse in certain directions under the application of an external electric field [3][4]. Polarization rotation from the tetragonal to rhombohedral phase and vice versa through intermediate monoclinic phase is found to be the reason for this extraordinary piezoresponse [5]. The application of an electric field which is not in alignment with the c-axis of the crystal would result in the phase transformation causing a variation in strain, which leads to an extraordinary piezoresponse. First principles molecular dynamics simulations have shown that, in BaTiO3, the phase transition through the monoclinic phase facilitates polarization reversal at a low electric field [6]. It was also shown that, when the p
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