Effect of lead titanate-zirconate additions into barium titanate ceramics on the dielectric and piezoelectric properties of mixed compounds

Powders of barium titanate (BT) and lead zirconate-titanate (PZT) were mixed together to form solid solutions in the ceramic system (1 - x)BT (.) xPZT, where 0 <= x <= 1. The mixed compounds were synthesized by sintering pressed samples of the mixed powders at high temperatures between 1100-1400 degrees C, for 3 hours. Dielectric and piezoelectric properties of the sintered samples were investigated at room temperature. X-ray diffractograms showed that monophase ceramics with perovskite structure were formed along the whole compositional range. The dielectric permittivity epsilon(r) increased with increasing amount of PZT, reaching a maximum value of about 6900 for composition with x = 0.6, and then suddenly decreases up to lower values of less than 2000. The piezoelectric properties (electromechanical coupling coefficient k(p), voltage and charge constants g and d respectively) behave as follows: at first there is a slight decrease of their values for all compositions with x <= 0.6 and then suddenly, and rather constantly, their values increase by more than 100 % for compositions with x >= 0.6. Such a behavior could possible be explained in terms of the structural changes brought about by the incorporation of PZT phase into BT one. The mechanical mixture of BT and PZT particles of similar dimensions gives rise to both new compositions as well as to distinct particles of BT or PZT of different dimensions under the influence of temperature, whose properties may differ from the initial ones so that their properties can be either the result of a size effect or the compositional one, but most probably the combination of both.