On the Firing Process and the Electrical Properties of Barium Titanate Ceramics

Abstract

The continuous-dilatometric method for the measurement of the change of dimension during the firing of the equimolecular mixture of BaCO3 and TiO2, the X-ray diffraction for following after the reaction and the formation of BaTiO3, and the electron microscope for the observation of the progress of grain growth, were used for the investigation of the relation between the growth of microcrystals and some electric properties, especially the D. C. break down voltage and hysteresis curves with results as follows:(1) BaTiO3 was formed from about 700°C and finished at the temperature of maximum expansion (at about 1100°C), which suggest the existence of a close relation between the anomalous expansion and the formation of BaTiO3.(2) The microcrystals began to grow from about 1250°C, which was accompanied by the rapid increase of relative permittivity. The Curie point, however, remained unaffected by the change of firing temperature from 1200°-1400°C.(3) The trend of rather decreasing break down voltage by the overgrowth of the microcrystals was observed.The relation between the break down voltage and the thickness of the specimen and the holding time at the maximum firing temperature (1360°C) was found to be expressed by;2 hrs holding Vc 2hr=9×d0.726 (kV)16 hrs holding Vc 16hr=6.7×d0.788 (kV), where Vc is the break down voltage, and d the thickness in mm.(4) Hysteresis curves showed that space charge polarization is more liable to occur by the incomplete growth of microcrystals.