Nanoscale Ferroelectric Properties of PZN-PT Single Crystals Studied by Scanning Force Microscopy
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Nanoscale Ferroelectric Properties of PZN-PT Single Crystals Studied by Scanning Force Microscopy I. K. Bdikin, V. V. Shvartsman, and A. L. Kholkin Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal ABSTRACT High-resolution domain studies were performed in Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZNPT) single crystals via piezoresponse force microscopy (PFM). Irregular domain patterns with the typical sizes of 20-100 nm were observed on the (001)-oriented surfaces of unpoled samples. On the contrary, (111) crystal cuts exhibited normal micron-sized regular domains with the domain boundaries directed along allowed crystallographic planes. The existence of nanodomains in (100)-oriented crystals was tentatively attributed to the relaxor nature of PZNPT where small polar clusters were predicted to exist upon zero-field cooling. These nanodomains were considered as the nuclei of the opposite polarization state that ease the switching process for this particular crystal cut. Local piezoelectric hysteresis was also performed by PFM on the nanometer scale. Similar switching behavior of (111)- and (100)oriented PZN-PT crystals suggests that their superior piezoelectric properties can be related to the domain wall motion rather than to the perovskite lattice itself. INTRODUCTION The nature of the excellent electromechanical properties of ferroelectric single crystals of solid solutions (1-x)(PbZn1/3Nb2/3)O3-xPbTIO3 (PZN-PT) is intensively investigated during last several years. These crystals are expected to replace traditional piezoelectric materials such Pb(Zr,Ti)O3 in actuators, transducers and smart systems. The attracting feature of this and similar systems is the extremely high piezoelectric effect (piezoelectric coefficient up to 2500 pm/V) and electrically induced strain (up to 1.7%) measured for (100)-cut faces of rhombohedral crystals of the composition close to the phase boundary with tetragonal phase (x∼0.08-0.1) [1]. It was also observed that the corresponding coupling coefficients are very high (~95%) making these crystals a promising material for piezoelectric transducers for medical imaging, active vibration damping, and underwater sensing [2,3]. It was clearly shown [4] that unusually high strain in these crystals is somehow related to the phase transition from rhombohedral to tetragonal phase under high electric field applied along the pseudocubic direction. For compositions close to the morphotropic phase boundary (MPB) a new monoclinic phase (intermediate between rhombohedral and tetragonal phases) has been observed by both x-ray diffraction and direct domain study [5,6]. This phase provides the possibility of domain rotation between rhombohedral and tetragonal phases and was suggested as a reason for the extraordinary electromechanical response of PZN-PT under applied electric field [7]. Several domain studies have been performed on PZN-PT crystals that revealed the existence of ferroelastic twins that exist even in poled specimens [8,9]. The disadvantage of
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