Synthesis of Y‐Doped BaTiO3–(Bi1/2K1/2)TiO3 Lead‐Free Positive Temperature Coefficient of Resistivity Ceramics and Their PTC Effects

As a lead‐free positive temperature coefficient of resistivity (PTCR) material, (1– x mol%) BaTiO 3 – x mol% (Bi 1/2 K 1/2 ) TiO 3 – y mol% Y 2 O 3 –0.5 mol% TiO 2 (BT– x BKT–2 y Y–0.5TiO 2 ) systems were prepared by the conventional solid‐state reaction method. All samples containing <2 mol% BKT sintered in air possessed relatively low room‐temperature resistivity (ρ 25 ) and high positive temperature coefficient (PTC) effect. However, when the BKT content exceeded 2 mol%, the sample was not semiconductive after sintering in air. The effects of sintering schedule on the properties of PTCR ceramics were discussed. The results showed that the optimum composition of BT–1BKT–0.2Y–0.5TiO 2 , sintered at 1330°C for not‐soaking and then fast quenched in air, achieved rather low ρ 25 of 28 Ω·cm and a high jump of resistivity (maximum resistivity [ρ max ]/minimum resistivity [ρ min ]) of 4.0 orders of magnitude with T c about 155°C. The ρ 25 of the as‐sintered sample could be further reduced to about 10 Ω·cm by annealing in N 2 at 450°C for 30 min, accompanied decrease on the PTC effect.