PTCR Behavior of CuO-Doped Ba_0.96(Bi_0.5K_0.5)_0.04TiO₃ Ceramics

Abstract

As a candidate of a lead-free positive temperature coefficient of resistivity (PTCR) material, Ba_0.96(Bi_0.5K_0.5)_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 Ba_0.96(Bi_0.5K_0.5)_0.04TiO₃ ceramics sintered at 1360°C for 3h in N₂ exhibited a tetragonal structure at room temperature. The PTCR characteristics of Ba_0.96(Bi_0.5K_0.5)_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 could act as sintering aids to promote grain growth and all the samples showed NTC effect.

Keywords:

• BaTiO₃
• K_0.5Bi_0.5TiO₃
• CuO-doped
• PTC effect
• Curie temperature

Funding

This research was supported by the National Natural Science Foundation of China (51372144), the New Century Excellent Talents Program of Chinese Education Ministry (NCET-11–1042), the Key Program of Innovative Research Team of Shaanxi Province (2014KCT-06) and the International Science and Technology Cooperation Project Funding of Shaanxi Province (2012KW-06).