Sintering Characteristics in BaTiO ₃ –Nb ₂ O ₅ –Co ₃ O ₄ Ternary System: I, Electrical Properties and Microstructure

Abstract

The influences of the Nb/Co ratio on electrical properties, densification behavior, and microstructural evolution were investigated on ceramics in the ternary system BaTiO 3 ‐Nb 2 O 5 ‐Co 3 O 4 . Temperature‐stable dielectrics were obtained using either a large amount of Nb + Co or a large Nb/Co ratio. The sintering characteristics and electrical properties were studied for the niobium‐rich composition (Nb/Co = 3.00; Comp.N) and the cobalt‐rich composition (Nb/Co = 1.67; Comp.C) with the same Nb + Co amount of 2 at.%. The temperature characteristic of the dielectric constant was flat, irrespective of the firing temperature, for Comp.N, whereas it was dependent largely on the firing temperature for Comp.C. The grains did not grow in Comp.N but grew in Comp.C. The reaction of Nb 2 O 5 and Co 3 O 4 with BaTiO 3 yielded secondary phases: Ba 6 Ti 17 O 40 phase for Comp.N, and a barium‐poor, titanium‐rich, and cobalt‐rich phase for Comp.C. These secondary phases formed a liquid phase during firing. Comp.N contained a larger amount of the secondary phase than Comp.C. It was concluded that the liquid phase contributed little to densification and microstructural evolution in the system BaTiO 3 ‐Nb 2 O 5 ‐Co 3 O 4 .