Processamento de varistores de baixa tensão à base de CCTO

Abstract

CaCu3Ti4O12 (CCTO) is a complex oxide of perovskite-like structure that has been widely studied due to its dielectric and non-ohmic properties. The morphology and composition of grains and grains boundary are crucial factors for the improvement of these properties. In this work, CCTO-based ceramics were processed through solid state reaction in different calcination (700 ºC, 800 ºC, 900 ºC and 1000 ºC, for 4 h) and sintering (1050 ºC and 1100 ºC for 2 h and 6 h) conditions, aiming to optimize varistor-capacitor properties. The materials obtained were characterized using X-ray diffraction (XRD), powder granulometric distribution, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electrical measurements. The XRD results showed formation of CCTO phase in all calcined powders. However, samples calcined at 700 ºC, 800 ºC and 900 ºC also presented secondary phases (TiO2 and CuO). The granulometric distribution of these samples was bimodal while samples calcined at 1000 ºC showed monomodal distribution. This effect influenced the pellet sintering, increasing the relative densification percentage, reaching 92,6 % for 900 ºC and sintered at 1100 ºC for 6 h and 90,6 % for 800 ºC sintered under the same conditions. The best results of electrical measurement obtained were ’ 1.9 x104 and  7.37 for samples calcined at 900 ºC, sintered at 1100 ºC for 6 h. The total processing time was shorter than that found in the literature by this synthesis method.