Nb‐Doped 0.9BaTiO₃–0.1(Bi_0.5Na_0.5)TiO₃ Ceramics with Stable Dielectric Properties at High Temperature

Abstract

Nb‐doped 0.9BaTiO3–0.1Bi0.5Na0.5TiO3 (0.9BT–0.1BNT) ceramics were prepared by conventional solid‐state method. The dielectric and the structural properties were investigated. It was found that the temperature–capacitance characteristics greatly depended on Nb2O5 content. With the addition of 2.0 mol% Nb2O5, 0.9BT–0.1BNT ceramic sample could satisfy the EIA X9R specification. This material was promising for high‐temperature MLCC application. Microstructure element distribution was studied using TEM and EDS. The Bi and Na were almost homogeneously distributed except grain‐boundary segregation of Bi. The Nb exhibited a nonuniform distribution from the grain boundary to the interior, showing the simultaneous presence of Nb‐rich and Nb‐poor regions. Such microheterogeneity gave rise to the temperature stability of permittivity. The solution‐precipitation mechanism was introduced to elucidate the evolution of microstructures. Degradation and recovery of insulation resistance were observed under a dc bias at 200°C, which was attributed to the electromigration and diffusion of Na+.

Effect of Ta2O5 and Nb2O5 Dopants on the Stable Dielectric Properties of BaTiO3–(Bi0.5Na0.5)TiO3-Based Materials

“…This observation is in accord with those reported in the literature [25,26]. In addition, the peaks corresponding to BaTiO3 in the XRD patterns shifted to lower angles due to the incorporation of the smaller ions Na into Ba sites leads to strengthened Ti-O bonds, and more energy is needed to maintain the balance of Ti 4+ displacement in the TiO6 octahedrons; thus, Tc increased [14,15,19]. The dielectric constant of (1 − x)BaTiO3-x(Bi0.5Na0.5)TiO3 at 25 °C decreased from 2066 to 677 while the tanδ value increased from 2.9% to 3.5% as the x value increased from 0.05 to 0.2.…”

“…The microstructures of the fracture surfaces indicated that all fractures were transgranular mode and revealed the presence of very little porosity. Figure 3a,b show the sintered surface and fracture surface of the pure 0.9BaTiO3-0.1(Bi0.5Na0.5)TiO3 ceramic sintered at 1215 °C, which included fine equiaxed grains with an average grain size of 0.57 μm and rod-like grains with a size of approximately 3.2 μm, similar to those reported in the literature [14]. The microstructures of the sintered surfaces and fracture surfaces of the 0.9BaTiO3-0.1(Bi0.5Na0.5)TiO3 ceramics with 1.0 and 2.0 mol% Ta2O5 sintered at 1215 °C are shown in Figure 3c,d, and in Figure 3e,f, respectively.…”

“…While the sintering temperature of BaTiO3 is typically above 1300 °C, the addition of (Bi0.5Na0.5)TiO3 significantly reduced the sintering temperature to 1230 °C for an x value of 0.05 and to 1215 °C for x values of 0.1 and 0.2, which was caused by the formation of the liquid phase [14,25]. XRD results indicated the presence of the tetragonal BaTiO3 perovskite phase (tetragonal, P4/mmm; JCPDF 75-0462) with trace amounts of second-phase Ba6Ti17O40 (monoclinic, C2/c; JCPDF 77-1566), which increased with the (Bi0.5Na0.5)TiO3 content.…”

“…The distortion and deformation of BaTiO3 structure induced by the substitution of Na into Ba sites by (Bi0.5Na0.5)TiO3 addition improves the stable temperature characteristics of the dielectric properties of BaTiO3. With the addition of Co3O4 and Nb2O5, the stable dielectric properties of BaTiO3-(Bi0.5Na0.5)TiO3 were tailored to meet the X9R specification by adjusting the core-shell structure [14,15]. It was also shown in the literature that the dielectric properties of BaTiO3 or bismuth-based compounds can be significantly enhanced with the addition of Ta2O5, through tailoring the microstructure, improving densification, and shifting Curie temperature [23,24].…”

“…The utilization of an effective Curie-point shifter, such as (Bi0.5Na0.5)TiO3 or PbTiO3, to increase the Tc point along with the formation of the core-shell structure was found to be an effective method for obtaining high-temperature stability [12][13][14][15][16]. Dielectric formulations, including BaTiO3-based compositions, such as BaTiO3-(Bi0.5Na0.5)TiO3 [5,7,8,14,[17][18][19], BaTiO3-Bi(Zn0.5Ti0.5)O3 [16,20], and BaTiO3-Pb(Ti0.55Sn0.45)O3 [10] systems, and (Bi0.5Na0.5)TiO3-based compositions, such as (Bi0.5Na0.5)TiO3-BaTiO3-CaTiO3 [6,9,21] systems, have been developed recently to meet the temperature coefficient of capacitance (TCC) requirements of the X9R specifications. Another approach was a multi-phase composite consisting of a high-Tc material and a low-Tc material.…”