Sintering Characteristics in BaTiO₃–Nb₂O₅–Co₃O₄ 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 role of Co in the BaTiO3–Na0.5Bi0.5TiO3 based X9R ceramics

“…In addition, a prerequisite to obtain the temperature stability is to keep the intensity of core peak and shell peak comparable, where a suitable Nb/Co ratio is desired to control the percentage of core part. The Co has a higher diffusivity than Nb which was demonstrated in the diffusion couple experiments [1,8], while the diffusion of Co was suppressed when the sample was co-doped with sufficient Nb. Therefore, sufficient amount of Nb was needed to control the so-called "co-solubility" of Nb and Co as a complex ½Nb 5 þ 2=3 Co 2 þ 1=3 4 þ or ½Nb 5 þ 1=2 Co 3 þ 1=2 4 þ .…”

“…As pointed out by Burn [7], small amount of Co could modify the Nb distribution and the reaction with BT affect the Curie point of BT, while Hennings [2] reported that in the case of combinatory addition of Nb and Co, the Co additive not only regulate diffusion and incorporation of Nb, but also influence the temperature stability of the system. In addition, the diffusion couple experiments carried out by Chazono and Kishi [1,8] revealed that the Nb/Co ratio played an important role to maintain the core-shell structure in BT-Nb-Co system. Therefore, it is possible to achieve X9R specification by regulating the existing core-shell structure in BT-NBT based system with Co addition.…”

“…BaTiO 3 -Nb 2 O 5 -Co 3 O 4 [1,2], BaTiO 3 -MgO-Ho 2 O 3 [3] etc.) have been actively studied for commercial multilayer ceramic capacitors (MLCCs) in last few years.…”

Synthesis of inside-out core–shell perovskite-type oxide nanopowder

“…Perovskite-type oxides nanoparticles with a "regular" core-shell structure, i.e., undoped core and doped shell, have been extensively investigated [16][17][18][19][20][21]. Such structure tends to be formed spontaneously during sintering.…”

Effects of core/shell volumetric ratio on the dielectric-temperature behavior of BaTiO3

“…The shell phase is clearly distinguished from the core region by both its morphology (rare ferroelectric domains) and chemical composition (high concentration of additives). When a core/shell structure forms, the dielectric-temperature behavior of the sample is typically improved, showing insensitive variation of the dielectric properties in a wide temperature range while also satisfying industrial standards [8][9][10]. Because of its positive effect on dielectric behavior, the core/shell structure of BaTiO 3 has won attention from many researchers [2][3][4][5][6].…”