PTCR Behavior of CuO-Doped Ba0.96(Bi0.5K0.5)0.04TiO3 Ceramics

As a candidate of a lead-free positive temperature coefficient of resistivity (PTCR) material, Ba0.96(Bi0.5K0.5)0.04TiO3-xCuO (x = 0–0.80%) ceramics were prepared by the solid-state reaction technique. X-ray diffraction results indicated that the CuO doped Ba0.96(Bi0.5K0.5)0.04TiO3 ceramics sintered at 1360°C for 3h in N2 exhibited a tetragonal structure at room temperature. The PTCR characteristics of Ba0.96(Bi0.5K0.5)0.04TiO3-xCuO ceramics were investigated in terms of CuO content. The undoped sample sintered in N2 showed low resistivity and a small resistance jump. With the increasing CuO content, both the Curie temperature and the room-temperature resistivity increased. The Raman scattering spectra showed that the Cu2+ was partly reduced to Cu+ during sintered in N2 which increased the density of the grain surface acceptors and enhanced PTC effect without reoxidation process. In the range of 0.05 ≤ x ≤ 0.20%, the samples displayed a marked PTC effect. When x ≥ 0.40%, CuO and Cu2O in ceramic samples co...