Internal stress effect on the temperature dependence of the dielectric and lattice constant in Sm-doped BaTiO3 ceramics

The internal stress effect on the temperature dependence of the dielectric and lattice constant in a Sm-doped BaTiO3 ceramic was investigated using various particle sizes of starting barium titanate, pressure-dielectric spectroscopy and a high pressure X-ray diffractometer. The grain size was nearly proportional to the particle size of the starting barium titanate, while inversely proportional to the internal stress. A sudden change of internal stress occurred at a grain size of approximate to 2 mu m. Grain size refinement, as well as external pressure, shifts the lattice and dielectric anomaly T-c to a lower temperature, whereas T-2 is shifted to a higher temperature. For ceramics with a grain size of 2.6 mu m; T-1 decreases with increase in pressure, reaches a minimum value at 5 kbar and then increases. Three lattice anomalies existed for small grained ceramics (<2 mu m) irrespective of grain size and at pressures up to 100 kbar. In particular, the temperature dependence of the dielectric and lattice constant for small grained ceramics (<2 mu m) was less sensitive to external pressure in comparison to that of large gained ceramics (>2 mu m), which was attributable to the internal stress (>240 MPa).