Influence of calcium doping on microstructure, dielectric and electric properties of BaBi2Nb2O9 ceramics

Barium bismuth niobiate (BaBi2Nb2O9) ceramics modified by calcium were prepared by solid state synthesis and two-step sintering process. An impact of calcium substitution on the A site of perovskite block is presented. The investigations are focused on dielectric as well as electric aspects of the modification. The presented results reveal that the concentration of a space charge is not preserved, what is surprising due to the homovalent nature of the dopant and no reason for creating additional lattice defects and charges connected. However, not only the valence of ions, but also the calcium-oxygen and barium-oxygen bond strength should be taken into consideration. Since the calcium-oxygen bond is probably weaker the loss of the bismuth oxide is expected to increase with an increase in the calcium content. Such a scenario results in appearance of a large number of negative charge carriers connected with unsaturated oxygen ions.