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Session D40 - Poster Session I.
POSTER session, Monday afternoon, March 12
Exhibit Hall, Washington State Convention Center

[D40.051] A problem of solid state: "Relation between structure and electrical properties of different ferroelectric ceramic systems"

Martinez Eduardo (3. Centro de Investigación Científica y Educación Superior de Ensenada, CICESE, Ensenada, B.C., México, 22800.), Fundora Abel, Amorin Harvey, Garcia Santiago, Portelles Jorge (1. Facultad de Física-IMRE, Universidad de la Habana, Vedado, La Habana 10400, Cuba.), Siqueiros Jesus (2. Centro de Ciencias de la Materia Condensada, UNAM, Ensenada, B.C., México, 22800.), Ferroelectrics Material Group Collaboration, Applied Physics Group Team, Optical Properties Group in CCMC Team

We present three different ferroelectric ceramic systems of recent research La_0.03Sr_0.255Ba_0.7Nb_2-yTi_yO_6-y/2 (LSBNT), Sr_0.3Ba_0.7Ti_1-5/4yNb_yO_3 (SBNT), xPbTiO_3-(1-x)SrTiO_3 (PST). These systems permit us to study interesting phenomena related with the solid state as nature of ferroelectric-paraelectric phase transitions, iconmmenurated structures, antiferroelectricity, coalescence of crystalline phases and ferroelectric nucleation. Nature of the ferroelectric-paraelectric phase transition is studied by Thermoelectric Analysis for each system for different concentrations of doping or mixing. It was observed that the Curie temperature varies linearly with composition. This value reflects the cation distribution within each unit cell and the type of crystalline structure. The temperature dependence of the dielectrical permittivity presents strongly broadened curves, which suggest a non Curie-Weiss behavior near the transition temperature in each crystalline system . The diffuse phase transition coefficient was also determined and its value leads to the conclusion that the degree of disorder depends with the presence of the dopant. Transmission Electron Microscopy evidenced the existence of a superstructure associated to incommensurability in the crystal structure of the LSBNT ceramic. In the electron diffraction patterns it was possible to measure the location of the incommensurate superlattice spots to determine the structural variations. The possibility of an antiferroelectric state in LSBNT is analyzed based on dielectric hysteresis. Antiferroelectricity seemed to be stronger for higher titanium concentrations. In SBNT the displacement toward higher temperatures shown by T_max corresponding to the t/o and o/r transitions for the samples doped with y=0.01 and the fact that the maxima corresponding to those transitions are not present in samples with y=0.0 5 and 0.1 lead us to think in a coalescence of the three phase transitions. In PST we study the nucleation of the ferroelectric phase and its influence on the electrical properties.

Part D of program listing