Doping effect of Ta ions on microstructure and electrical properties of BaTiO-(BiNa)TiO ceramics with positive temperature coefficient of resistivity.

Lead-free 0.912BaTiO-0.088(BiNa)TiO- xTaO (0 ≤ x ≤ 0.005) ceramics with positive temperature coefficient of resistivity (PTCR) were prepared by solid reaction sintering of high-purity metal oxides and carbonates reagents. The doping effect of Ta ions on the microstructure and electrical properties of the samples was investigated. X-ray diffraction analysis indicated that all the samples were of a single tetragonal perovskite structure with the calculated c/ a value first increased and then decreased with increasing x. The Raman shift at 305 cm became strong firstly and then declined, and the broad band at 722 cm narrowed initially and then broadened with the increase in Ta content. The Curie temperature raised first and then decreased, presenting the highest value up to 170 °C for the samples with x = 0.001. Moreover, after the incorporation of Ta ions, the PTCR (defined by the resistivity jump with the ratio of maximum to minimum ones) decreased first and then increased, presenting the best PTCR performance for the samples with x = 0.005. And with increasing x, the room temperature resistivity decreased first and then increased, displaying the lowest room temperature resistivity for the samples with x = 0.003. [ABSTRACT FROM AUTHOR]