Influence of Cation Vacancies on the Ferroelectric Properties of SBT Doped with Praseodymium
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0966-T07-08
Influence of Cation Vacancies on the Ferroelectric Properties of SBT Doped with Praseodymium Jorge Mata1, Alejandro Durán1, Eduardo Martínez1,2, and Jesus Siqueiros1 1 Centro de Ciencias de la Materia Condensada, Universidad Nacional Autónoma de México, Apdo. Postal 2681, Ensenada, Baja California., 22800, Mexico 2 Centro de Investigación en Materiales, DIP-CUCEI, Universidad de Guadalajara, Apartado Postal 2-638, Guadalajara, Jalisco, 44281, Mexico
ABSTRACT Dielectric and ferroelectric properties were studied in Sr0.85-yPr0.15VyBi2Ti2O9 polycrystalline samples where cation vacancies were induced. DRX characterization shows that the Aurivillius structure can accept 10% of induced vacancies without precipitation of second phases. Thermoelectric analysis and ferroelectric hysteresis measurements show that the vacancies modify the transition temperature Tc and slightly the polarization values. From the ε-T curves it was observed that the polarization magnitude and Tc are affected as a consequence of the induced vacancies. A broad peak at Tc, typical of the diffuse phase transition behavior of this material was also observed. Furthermore, the induced vacancies in praseodymium-modified SBT produce an increased on Tc from ~180 to ~240 ºC, these facts show that induced vacancies in the structure are a tuning mechanism for the dielectric and ferroelectric properties.
INTRODUCTION Bismuth layer-structured ferroelectrics (BLSFs) are thought to be promising materials for lead-free ferroelectric oxides for device applications such as actuators, sensors and nonvolatile random access memories (NvRAMs). [1]. Ferroelectric SrBi2Ta2O9 (SBT) has a bismuth layered structure. Pseudo-perovskite blocks, (SrATa2O7)2-, composed of double TaO6 octahedra with Sr at the A site are interleaved with (Bi2O2)2+ layers. The (Bi2O2)2+ layers act as insulating layers and largely control the electric response, while the ferroelectricity arises mainly in the pseudoperovskite blocks. [2]. However, a disadvantage of SBT with respect to PZT is its small 2Pr value of about 14 µC/cm2 as compared with more than 50 µC/cm2 for PZT [1]. For SBT, the introduction of cation vacancies as well as the substitution of rare earth ions (RE) in the A site strongly affect the polarization-switching properties and leads to a decrease of the Curie Temperature (Tc) and an increase of the remanent polarization (Pr) [3 -4]. Studies in ferroelectrics ceramics have indicated that defects such as oxygen vacancies interact strongly with domain boundaries and have important influence on the polarization behavior [5]. Moreover, Noguchi et al. have demonstrated that B site doping into BLSFs leads to a much lower leakage current and larger remnant polarization [6]. These results have suggested that a large number of bismuth and oxygen vacancies exist in this structure and such defects have an important impact on the polarization and the electrical properties.
When defects have sufficient mobility for hopping in a ferroelectrics state, mobile vacancies can assemble i
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