BARIUM TITANATE STANNATE FUNCTIONALLY GRADED MATERIALS: CHOOSING OF THE Ti/Sn CONCENTRATION GRADIENT AND THE INFLUENCE OF THE GRADIENT ON ELECTRICAL PROPERTIES

摘要

Barium titanate stannate (BaTi_(1-x)Sn_xO_3, BTS) functionally graded materials (FGMs) with different Ti/Sn concentration gradients were prepared by the powder processing method followed by sintering. Firstly, with the aim of tailoring the concentration gradient of Ti/Sn, the main characteristics of BTS ingredients were studied. The influence of the Ti/Sn concentration gradient on the electrical characteristics of the FGMs was examined by impedance spectroscopy (IS). The grain-interior and grain boundary resistivity of the FGMs were distinguished and activation energies were calculated. It has been established that for the FGMs the activation energy deduced from the grain-interior conductivity (0.74-0.78 eV) is defined by chemical composition (intrinsic property) and that it does not depend on the Ti/Sn concentration gradient. Quite contrary, the activation energy for the grain boundary conductivity (1.03-1.29 eV) is determined by the microstructural gradient which is a direct consequence of the concentration gradient. The results of IS indicate that there are no insulator interfaces (cracks and/or delamination) between graded layers in FGMs. This assumption was confirmed by in situ monitoring of the sintering processes in thermal microscope, and furthermore, by SEM analysis of FGMs in cross-sectional view.