THE INFLUENCE OF SILICON ON MICROSTRUCTURE AND ELECTRICAL-PROPERTIES OF LA-DOPED BATIO3 CERAMICS

BaTiO3 positive temperature coefficient of resistance ceramics were prepared with the general composition (La0.002 Ca(x) Ba0.998-x) (Ti1.01-yMn(y) O3.zSiO2 and sintered in air. The Ca content as well as the amount of doped Mn were varied ranging from 4-20 mol % and 0.02-0.04 mol %, respectively. Up to 4 mol % Si was added using a new method as well as by the classical means as solid silica. In the new method, the desired quantity of Si(OC2O5)4 (Si(O Et)4), contained in dry tetrahydrofurane (THF), was dropped under a slight stream of inert gas into the vigorously stirred aqueous slurry which was manufactured after the calcination process. The addition of Si by this technique was found to result in a homogenization of the microstructure and an improvement in electrical properties. The effect of Si on electrical properties is explained by the influence of the observed second phase on the equilibrium of Ba vacancies. The results of further variation of Ca and Mn contents are presented.