Influence of Core‐Shell Grains on the Internal Stress State and Permittivity Response of Zirconia‐Modified Barium Titanate

Abstract

BaTi03 modified with grain-boundary resident ZrOl ( 5 2 wt%) results in substantial chemical modification of the microstructure when sintered at 1320°C for 2 h. These modified regions were seen as core-shell grains in the microstructure and were accompanied by an increase in the internal stress level. The shells had a variable composition (Ba(TiI-rZrx)03) and a tetragonal structure. An expansion mismatch between the core and the shell placed the core in compression resulting in a decrease in the lattice parameter and a pseudocubic structure with respect to the unmodified BaTi03. The combination of core-shell grains and increased internal stress resulted in an essentially flat permittivity response with temperature, a condition consistent with a distribution of Curie points within the ceramic. [

Influence of CaZrO3 on dielectric properties and microstructures of BaTiO3-based X8R ceramics

“…It should be noted that the c lattice parameter decreases monotonously ( Table 2). Armstrong et al figured that [7] the great internal stress caused by the high expansion shell forced a decrease in the c lattice parameter and thus tetragonality decreased. Figure 3(a) shows the temperature dependence of dielectric constant for all the samples.…”

“…It has been proved that the characteristic of broadened permittivity-temperature represents a diffuse phase transition (DPT) around T c, and this behavior was observed in BaTiO 3 with additive of ZrO 2 [5] . Armstrong and Lu et al [6,7] reported that ZrO 2 -modified BaTiO 3 showed a suppressed ferroelectric transition region by the influence of core-shell structure.…”

Microstructural Analysis of X7R-Type BaTiO3 Multilayer Ceramic Capacitors (MLCCs)

“…The core-shell structure boundary as indicated by A in Fig. 3(a) is suggested to be coherent [16][17][18]21]. The thickness of the domains varies between grains, but is generally less than 100 nm.…”

“…It is widely accepted that the presence of core-shell structures in ceramics is attributed to chemical inhomogeneity [15][16][17][18][19][20]. Armstrong and Buchanan [21] used convergent beam electron diffraction (CBED) in the transmission electron microscope (TEM) to determine that both the core and shell in zirconia-modified barium titanate were tetragonal phases at room temperature. However, cubic shell phases have also been reported by other researchers in barium titanate systems doped with other additives [19].…”

Oxidation-induced strain relaxation and related dielectric-temperature behavior in core/shell grained BaTiO3

“…Its dissipation factor is higher at low temperature than that of other samples. For such a difference in dielectric-temperature behavior among samples, several causes have been proposed, including differences in (a) the concentration of dopants in the shell [19,34], (b) the occupational site of rare-earth elements in the shell [16][17][18]35], (c) charge carrier concentrations and the resultant valence state of Ti [27,28], and (d) the residual strain [24,36]. In this study, the effect of the concentration of dopants can be excluded because all the samples were prepared under the same experimental conditions, except the oxidation temperature, which should not affect the distribution of dopants in the shell.…”