Dielectric Properties of Potassium Sodium Niobate Ceramics Prepared by Spark Plasma Sintering

Reference	Presenter	Authors (Institution)	Abstract
08-069	SILVANIA Lanfredi	Lanfredi, S.(Faculdade de Ciências e Tecnologia); Noudem, J.(Université de Caen Normandie); Nobre, M.A.(Faculdade de Ciências e Tecnologia); Lira, K.H.(Faculdade de Ciência e Tecnologia);	Potassium sodium niobate, K0.5Na0.5NbO3 (KNN), is one of the most promising lead-free materials. However, in conventional sintering the KNN presents low sinterability, since at high temperature occurs the volatilization of alkaline sodium and potassium. Promising techniques from application of an electrical current through the sample during heating has shown a rapid densification of ceramics. From these methods is possible to obtain dense ceramic in short time at relatively low temperatures. The most promising technique used among Field-Assisted Sintering Techniques is Spark Plasma Sintering (SPS). In this work KNN powders, prepared by polyol modified method, were heat treated using regular Spark Plasma Sintering-SPS and by the conventional sintering (CS) with the KNN powder pressed uniaxially into pellets and heated at 950 oC for 2 h in air. The phase compositions, grain texture, as well as microstructure of the samples were analyzed by X-ray diffraction and SEM studies and their electrical properties were investigated by impedance spectroscopy. Dielectric characterization was performed from room temperature to 650 °C, in the frequency range 5 Hz–13 MHz. The bulk permittivity was derived by the variation of the imaginary part of the impedance as a function of reciprocal angular frequency. The permittivity values as a function of temperature showed two maxima. The first maximum is very similar at 200 °C and the second one positioned at around 410 °C, which was associated to Curie’s temperature. KNN ceramic prepared from SPS with density at around 98 % presented at room temperature ?r = 610, which is about 30% higher than that of the CS sample. Differences between the SPS sintered and CS samples can be attributed to grain size effects.
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