Influences of Ba/Ti Ratios on the Positive Temperature Coefficient of Resistivity Effect of Y-Doped BaTiO3-(Bi1/2Na1/2)TiO3 Ceramics

Abstract

Y-doped (1−x mol%)BaTiO3–x mol%(Bi1/2Na1/2)TiO3 (BBNTx) lead-free positive temperature coefficient of resistivity (PTCR) ceramics were prepared using a conventional solid sintering method. The Ba/Ti ratio was adjusted to obtain the optimized PTCR property. The results show that all 0.2 mol% Y-doped BBNT15 samples with various Ba/Ti ratios have formed a single tetragonal perovskite phase by sintering in an N2 atmosphere. The sample with 5 mol% (Bi1/2Na1/2)TiO3 has only a minor PTCR effect (maximum resistivity [ρmax]/minimum resistivity [ρmin]) when sintered in N2. However, the PTCR effect is enhanced over 3.0 orders of magnitude when the (Bi1/2Na1/2)TiO3 content is >8 mol%. The PTCR characteristics of the samples with Ti excess are superior to those with Ba excess. The optimum composition of 0.2 mol% Y-doped BBNT15 with Ba/Ti=0.99, sintered at 1250°C for 3 h in an N2 atmosphere, has a low room-temperature resistivity (ρ25) of ∼100 Ω·cm and a high PTCR effect of ∼4.8 orders of magnitude with Tc around 190°C.