Piezoelectric effect in epitaxial PbZr 1-x TixO 3 thin films near morphotropic phase boundary region
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Sang Sub Kim Dept. of Materials Science and Engineering, Chonnam National University, Gwangju 500-757, Korea
Bongki Lee and Hyunjung Shin School of Advanced Materials Engineering, Kookmin University, Seoul 136-702, Korea
Sunggi Baika) Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea (Received 28 October 2004; accepted 19 January 2005)
The relationship between crystal structure and piezo-response was investigated in epitaxially grown PbZr1−xTixO3 (PZT) thin films on Pt(001)/MgO(001) with a thin PbTiO3 interlayer. Insertion of the interlayer resulted in significant relaxation of the strain that could be developed in the course of deposition of the PZT films, consequently leading us to single out only the effect of composition. Composition of the morphotropic phase boundary (MPB), at which tetragonal and rhombohedral phases are mixed with the same volume fraction, was found to be ∼0.55 in Ti/(Zr + Ti) ratio in our films, which is close to the value for bulk polycrystalline PZT (∼0.50). The piezoelectric response peaks were two times higher in the MPB regime than in the single phase regime due to structural instability caused by the coexistence of two phases. The results indicate that epitaxial PZT films having the MPB composition are advantageous over those of other compositions for nano-storage devices based on scanning force microscopy. Ferroelectric thin films of lead-based perovskite materials such as PbTiO 3 , (Pb x La 1 − x )TiO 3 (PLT), PbZrxTi1−xO3 (PZT), etc. have received considerable attention for their attractive physical properties including high dielectric, pyroelectric, piezoelectric, and electrooptic properties.1,2 Increasing demand for ultrahigh density information storage devices has brought about significant interest in the use of scanning force microscopy (SFM) for nanoscopic read/write operations with ferroelectric media. Since Hidaka et al.3 first proposed such a memory device, many observations using SFM have been demonstrated for the development of ultrahigh density information storage devices utilizing ferroelectric thin films.4–7 Maximization of d33-values is critical for fast reading and writing capability in SFM-based ferroelectric data storage devices.7 Recently, significant enhancement of d33 was discovered using SFM in epitaxial tetragonal PZT thin films as the films were patterned into small discrete islands.8,9 The enhancement of d33 values in the discrete islands in comparison with the continuous films a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0129 J. Mater. Res., Vol. 20, No. 4, Apr 2005
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was attributed to the a-domain switching facilitated by the removal of substrate clamping. We found recently that, even in continuous PbTiO3 thin films, a small amount of a domains switched above a certain electric field.10 However, its contribution to overall piezoelectric response was found to be insignificant in the conti
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