(Ba, Y)(Ti, Zr, Sn)O₃-based PTCR materials

Abstract

PTCR materials based on the systems (Ba, Y)(Ti_1−yZr_y)O₃ and (Ba, Y)(Ti_1−ySn_y)O₃ were investigated. It has been found that in the case of partial isovalent substitution of titanium ions by zirconium or tin ions, the grain size passes through a maximum at a concentration of 15 and 5 mol.% respectively. This may be attributed to the different grain growth mechanisms in the presence of a small and large amount of liquid phase. It has been shown that increasing the amount of isovalent substitution narrows the donor dopant concentration range, within which PTCR effect occurs. These results agree with the thermodynamic calculation of the range of existence of solid solutions (Ba, Y)(Ti_1−xM_y)O₃, which were regarded as a result of interaction between three phases with perovskite structure: BaTiO₃, YTiO₃ and BaMO₃ where M = Zr, Sn, and of the presence of complex centers Y³⁺-Ti³⁺, as indicated by ESR data.

Key Words:

• PTCR ceramic
• isovalent substitution
• grain size
• solid solution: thermodynamic