Thermal Analysis at Low and High Temperature and Evidence of Structural Transition Induced by Praseodymium in SrTiO3
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0966-T07-22
Thermal Analysis at Low and High Temperature and Evidence of Structural Transition Induced by Praseodymium in SrTiO3 Alejandro Durán1, Francisco Morales2, Luis Fuentes3, Javier Castro4, and Jesus Siqueiros1 1 Centro de Ciencias de la Materia Condesada, Universidad Nacional Autónoma de México, Ensenada B.C., 22800, Mexico 2 Instituto de Investigación en Materiales, Universidad Nacional Autónoma de México, Mexico, 04510, Mexico 3 Centro de Investigacion de Materiales Avanzados (CIMAV), Chihuahua, 13109, Mexico 4 Instituto de Ingenieria y Tecnologia, Universidad Autónoma de Cd. Juarez, Ciudad Juarez, Chiuh., 32300, Mexico
ABSTRACT To explore the nature of ferroelectric behavior induced by Pr ion in the SrTiO3 ceramic, we brought together a combination of Synchrotron x-ray powder diffraction and thermal analysis. Rietveld analysis shows a clear peak splitting strongly suggesting a cubic-tetragonal structural transition when 15 % Pr substitutes the Sr site. To determine the temperature of the structural instability differential thermal analysis at high temperatures (30-900 °C) and specific heat at low temperatures (2-300 K) were performed. The difference in the heat capacity for Pr doped and undoped samples are very small. A plateau in Cp/T vs T at 110 K is a clear evidence of the competing effect of two kinds of order parameters, one represented by the polarization and the other by the rotation of the oxygen octahedral in the perovskite structure. Upon heating, DTA analysis shows an unexpected single endothermal broad anomaly at about 118 °C. The occurrence of this thermal anomaly could be related to displacive structural contributions providing unambiguous evidence of diffuse phase transition. INTRODUCTION SrTiO3 (STO) is a prototype model (ABX3) of the basic perovskite system that displays a wide range of physical and chemical properties such as incipient ferroelectricity, semiconductivity, superconductivity and catalytic activity [1-4]. The crystalline structure is cubic down to 110 K where it transforms to tetragonal CaTiO3-type structure together with a strong elastic anomaly which produces an incipient ferroelectric phase [2]. The thermo-electric properties are heavily dominated by their oxygen content as well as by donor and acceptor-type impurities. It has been demonstrated that rare earth elements are substituted at the A-site as trivalent ions and that the charge neutrality is satisfied through the formation of oxygen vacancies acting as effective donors [5, 6]. On the other hand, it is known that there are different ways induce a polar state in STO; i. e., by application of a sufficiently strong electric field [7], by application of uniaxial stress [8], by isotope of oxygen anion [8] and by substitution of Sr cation, either iso- or heterovalent cations [10,11]. Dielectric anomalies with remarkable frequency dispersion at low temperature were obtained for nonisovalent substitution of Sr by rare earth ions [12]. Doping with Pr at the Sr site has not been systematically studied at low temperature.
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