Effects of different bismuth-based compounds additives on the positive temperature coefficient effect of BaTiO3 ceramics

As a candidate for lead-free positive temperature coefficient of resistivity (PTCR) ceramics, BaTiO3 (BT) ceramics with different Bi-based compounds (K0.5Bi0.5TiO3, BaBiO3, Bi4Ti3O12 and Bi2O3) were fabricated by a conventional solid state reaction. The effects of Bi-based compounds additives on the phase composition, microstructure and PTCR characteristics of BT ceramics were investigated with X-ray diffraction, scanning electron microscope, and resistivity-temperature measurement instrument. The results showed that the average grain size, the Curie temperature (Tc) and the room temperature resistivity (ρRT) of BT ceramics varied with the additives of Bi-based compounds. The minimum value of ρRT for BT ceramics with different Bi-based compounds could be obtained when the atom concentrations of bismuth were around 0.2%. The ceramic samples showed a moderate PTCR effect, with a resistance jump greater by 1.4–3 orders of magnitude and increased Tc about 120–132 °C, along with a low resistance of 4–1500 Ω cm.

► Tc had an increasing tendency in different degrees with different Bi-based compounds contents.
► The minimum value of ρRT when the concentration of Bi3+ was around 0.2%.
► ρRT firstly decreased and then increased with increasing Bi3+ content.
► The resistance jump greater by 1.4–3 orders of magnitude can been attained.