Semi-oxalate synthesis of (1-x)BaTiO₃-xM_0.5Bi_0.5TiO₃ (M = Li, Na, K) PTCR materials

(1-x)BaTiO₃–xM_0.5Bi_0.5TiO₃ (M = Li, Na, K) solid solutions were prepared using BaTiO₃ pre-synthesized by oxalate method. The stability limits of (1-x)BaTiO₃–xLi_0.5Bi_0.5TiO₃ solid solutions have been established. It was shown that increase in M_0.5Bi_0.5TiO₃ concentration results in reduction of ceramic grain size in the (1-x)BaTiO₃-xM_0.5Bi_0.5TiO₃ (M = Li, Na, K) system. It was found that the positive temperature coefficient of resistance (PTCR) effect in lead-free materials is due to the presence of a semiconductor core, which is formed by sintering under reducing atmosphere, and dielectric grain boundaries, formed on additional oxidation in air. The use of barium titanate, pre-synthesized by oxalate method, in the synthesis of solid solutions reduced the sintering temperature of ceramics compared with solid state reaction technique. By comparing the electrical properties of the synthesized lead-containing and lead-free materials, it has been shown that lead-free materials exhibit better electrical properties for practical use compared with lead-containing materials.