Ferroelectricity in SrTiO 3 Ceramics Induced by Pr Doping
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Ferroelectricity in SrTiO3 Ceramics Induced by Pr Doping A. Durán, E. Martínez, J. Mata, J. Heiras, *X. Solans, J. Siqueiros Centro de Ciencias de la Materia Condensada, Universidad Nacional Autónoma de México, Apdo. Postal 2681, Ensenada Baja California, 22800 MÉXICO. *Departament de cristallografia, Universitat de Barcelona-E08028, Barcelona Spain. ABSTRACT Ferroelectricity was induced in SrTiO3 by the Sr exchange for Pr ion in the A site of the perovskite ABO3-type structure. X-ray diffraction patterns show single phase crystalline structure in the SrxPr1-xTiO3 compound for x=0, 0.025, 0.050, 0.075 and 0.1 compositions. Rietveld refinement shows that the unit cell volume decreases with the increasing of Pr content as a consequence of the difference between Sr/Pr ionic radii. Furthermore, high-temperature differential thermoanalysis (DTA) displays a small anomaly at about 118 0C which is probably due to the Pr ion producing a distortion of the perovskite structure via an off-center site. This deformation in the lattice induces a measurable polar behavior of the solid solution. Dielectric permittivity (ε vs T) measurements display a well defined peak at about 238 0C. Furthermore, a well defined hysteresis loop at 30 0C with a remnant polarization that tends to decrease with increasing Pr concentration is observed. Both experimental results confirm the ferroelectric state induced by the Pr ion. INTRODUCTION SrTiO3 (STO) is a simple perovskite compound and is one of the most widely studied materials in solid state physics and chemistry. Extensive investigations have been performed in this material and related compounds not only for applications to practical devices but also for elucidating and exploring new properties of oxides. It exhibits quantum paraelectricity [1] as well as induced ferroelectricity by an electric field, uniaxial stress, and ion substitutions [2-4]. Although the best dielectric properties are found at low temperatures, it is widely known that a wide variety of solid solutions with a prototype STO perovskite can be prepared by single or multi-elemental substitutions at the Sr or Ti sites. Selections of constituents are based on factors that mainly include charge neutrality, structural tolerance factor and solubility. Substitutions of lanthanides or group II A elements (Ca, Ba) at the Sr site and zirconium with different Zr/Ti ratios have provided many solid solutions for numerous industrial applications [5]. In the present study, we show that praseodymium substitution in the Sr-site leads to lattice deformation and the polarization measurements reveal that the Pr-ion induced ferroelectric behavior at room temperature. EXPERIMENTAL PROCEDURE The Sr1-xPrxTiO3 with x=0, 0.025, 0.050, 0.075 and 0.1 samples have been synthesized by solid-state reactions. Starting materials were high purity (>99.9 %) SrCO3, Pr6O11 and TiO2. The powders were milled, calcined at 1100 0C in air, pressed into pellets and again calcined at 1300 0 C. After 5 h they were quenched in a box furnace at room temperature.
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