Float-Zone Growth and Properties of Ferroelectric Lead Titanate
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G.A. Rossetti, Jr. Department of Ceramic and Materials Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08855 (Received 7 October 2003; accepted 20 November 2003)
Lead titanate (PbTiO3) is a ferroelectric/piezoelectric material widely used in medical ultrasound transducers and infrared detectors. It is also important as an end member of morphotropic solid-solution systems such as Pb(Zn1/3Nb2/3)–PbTiO3 (PZN–PT) and Pb(Mg1/3Nb2/3)–PT (PMN–PT) that exhibit exceptional electromechanical properties as oriented single crystals. The float-zone technique has been used to grow pure crystals of lead titanate. To the best of the authors’ knowledge, this is the first time that the growth of this compound by the float-zone technique has been reported. The principal advantage of the float-zone technique is that no container is required so that a uniform distribution of chemical constituents can be obtained while eliminating problems of heterogeneous nucleation and metal contamination at the container wall. Although large single crystals were not obtained in the current study primarily due to instabilities of the molten liquid zone, the combined results of characterization by electron probe microanalysis, x-ray diffraction, specific heat, and dielectric permittivity measurements show that the float-zone crystal growth technique can produce lead titanate crystals of high chemical and phase purity. However, the results show that to obtain large single crystals, the stability of the molten zone at low cooling rates must be improved. I. INTRODUCTION
Lead titanate, PbTiO3, is an important compound in the large family of perovskite ferroelectrics. At its Curie temperature, Tc ⳱ 490 °C, it undergoes a first-order phase transition from a cubic (Pm3m) prototype to a tetragonal (P4mm) ferroelectric phase. Of the perovskite ferroelectrics for which the lattice dynamics have been studied in detail, the phase transition and soft-mode behavior in lead titanate most closely approximates that expected at the displacive limit.1 The transition is accompanied by unusually large and abrupt discontinuities in the dielectric susceptibility, the spontaneous polarization, the specific heat, and other physical properties. Furthermore, at room temperature, the tetragonal distortion involves a large displacement of the titanium atom along the polar axis that gives rise to a spontaneous polarization that is exceptionally high (Ps ∼75 C/cm2). Because of these attributes, lead titanate is an extremely attractive candidate for sensing and high frequency/ medical ultrasound applications.1 Lead titanate is also important as an end member of morphotropic solidsolution systems such as Pb(Zn1/3Nb2/3)–PbTiO3 (PZN– PT) and Pb(Mg1/3Nb2/3)–PT (PMN–PT) that exhibit exceptional electromechanical properties as oriented single a)
Address all correspondence to this author. e-mail: [email protected] © Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2003.
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