Electrical properties of barium titanate stannate functionally graded materials

Abstract

Barium titanate stannate (BTS) functionally graded materials (FGMs) with different tin/titanium concentration gradient were prepared by the powder-stacking method and uniaxially pressing process, followed by sintering. Impedance spectroscopy (IS) was used to determine the electrical characteristics of FGMs and ingredient BTS ceramics, as well as to distinguish the grain-interior and grain boundary resistivity of the ceramics. Activation energies of FGMs and ingredients were calculated. It has been established that for BTS ceramics the activation energy deduced from grain-interior conductivity (0.73-0.75 eV) is defined by chemical composition, while activation energy for grain boundary conductivity (1.07-1.25 eV) is influenced by microstructural development (density and average grain size). Furthermore, for FGMs, activation energy for grain-interior conductivity kept the intrinsic properties (0.74-0.78 eV) and did not depend on tin/titanium concentration gradient, while activation energy (1.03-1.29 eV) for grain boundary was determined by the microstructural gradient. No point dissipation was observed by IS, accordingly, no insulator interfaces (cracks and/or delamination) between graded layers were detected. © 2009 Elsevier Ltd. All rights reserved.