Dielectric Properties of Mixed Crystals of Barium-Strontium Titanate

Abstract

Mixed crystals of (Ba-Sr)TiO 3 containing up to about 10 mole per cent of Sr were grown in the same triangular plate shape as BaTiO 3 single crystals, and dielectric measurements were performed thereon. Up to 2.25 mole per cent Sr, the dielectric constant vs temperature ( ε -T) curve near the cubic-tetragonal transition temperature maintains the same form as that of pure BaTiO 3 , the peak value rising with increasing Sr content. Above 5.64 mole per cent Sr, however, the ε -T curve has a rounded peak and the peak value drops remarkably. The temperature of maximum dielectric constant decreases with increasing Sr content at a constant rate of 2.9°C per mole per cent in spite of this change. The Curie-Weiss temperature also drops with increasing Sr content at nearly the same rate, the difference between these two temperatures being held at about 20°C. The Curie constant also seems to decrease slightly with increasing Sr content. A comparison between the effect of replacing Ba with Sr and the effect of hydrostatic pressure on the transition temperature and the lattice constant suggests that the transition temperature depends mainly on the lattice constant of the tetragonal c-axis.