Effect of wettability of grains by a liquid phase on grain growth behavior of La-doped SrTiO3 ceramics

Abstract

The relationship between the grain growth and the wettability of grains by a liquid phase was discussed on the basis of the observation of the microstructure of La-doped SrTiO3 ceramics and the measurement of the contact angle of the liquid phase (Sr1Ti3.206La0.328O7.904) on the SrTiO3 substrate using the sessile drop method. The contact angle of the liquid phase in SrTiO3, which was the composition at 1490°C as determined from the SrO-TiO2 phase diagram, on the SrTiO3 substrate was 22°. The contact angle of the liquid phase containing La2O3 was 22°. The contact angles of the liquid phases in the cases of SrTiO3 containing SiO2 and a mixture of SiO2 and Bi2O3 were 16° and 9°, respectively. The contact angle was decreased by the addition of SiO2 and/or Bi2O3. The liquid phase of La-doped SrTiO3 ceramics was considered to have relatively poor wetting and to localize at the triple grain junctions at high temperatures and then to be exuded from the inner part to the surface of the samples during cooling. The nucleation and grain growth occur at this spot where the liquid phase is present. Thus, exaggerated grain growth occurs. The number of nuclei increases with the increase of the volume of liquid phase upon increasing the Ti/Sr ratio, which leads to the inhibition of grain growth. On the other hand, since the liquid phase of La-doped SrTiO3 containing SiO2, Bi2O3 can uniformly wet the grains, the growth rates of all grains are almost the same and exaggerated grain growth is not observed.