resumo
Stoichiometric Potassium Sodium Niobate (K0.5Na0.5NbO3) has been suggested as a capable substitute to lead-based piezoelectric sensors, actuators, among others. Moreover, KNN has a high curie temperature (TC) higher than the most used lead based piezoelectrics, PZT [Pb(ZrxTi1-x)O3], which enables KNN to be used as high temperature piezoelectric. However, high performance piezoelectric materials demand high densification. KNN processing is not trivial, mostly due to volatilization of alkalis and segregation of secondary phases that occur during sintering. FLASH sintering is a recent technique to densify ceramics at significantly lower temperature and time than conventional processes. It consists in applying an electric potential along with heating. When the threshold in conductivity occurs, the material densifies in less than 60 s, in a current control regime. In this work, FLASH sintering of KNN was performed, avoiding formation of secondary phases and the electrical behavior of the sintered samples is reported. KNN specimens were FLASH sintered below 900 ºC, with an electric field of 350 V/cm and current limit of 15 and 20 mA/mm2. Microstructure was accessed by SEM and phase composition by XRD. FLASH KNN ceramics exhibit some microstructural heterogeneities in the densification, grain growth and grain morphology. Permittivity change with temperature and frequency, P-H loops and d33 coefficient were accessed.
autores
Ricardo Serrazina, Paula Vilarinho, Ana Senos, Luís Pereira
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