Core–Shell Structure Analysis of BaTiO₃ Ceramics by Synchrotron X‐Ray Diffraction

Abstract

The shell thickness of a BaTiO3 ceramic with a core–shell structure has been measured by means of synchrotron X‐ray diffraction (XRD). BaTiO3 ceramic is known from transmission electron microscope (TEM)/energy dispersive X‐ray spectroscopy (EDS) observations to have an inhomogeneous microstructure with cores of a pure BaTiO3 and shells doped with additives. It is also known, from XRD observations, that the BaTiO3 cores have a tetragonal lattice structure and the shells are pseudocubic. We have estimated the shell thickness d from the full‐width at half‐maximum (FWHM) of the cubic (400)c peak, using Scherrer's equation. The shell thickness dcal was also evaluated from the volume fraction of tetragonal BaTiO3 using a spherical core–shell model. The two values thus determined agree well, confirming that the BaTiO3 ceramic specimens have a core–shell structure. Our results show that synchrotron XRD is a simple and effective tool for quantitative analysis of the core–shell structure. It enables us to understand quantitatively the relationship between the microstructure and the dielectric properties of BaTiO3 ceramics.

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

“…It is, therefore, difficult to differentiate the effects of the two parameters, the thickness and composition of the shell, on dielectric-temperature properties. Yasukawa et al [25] observed a similar variation of dielectric-temperature properties with increased ball milling time. In their case, however, as the ball milling time increases, the chemistry in the shell as well as grain size vary considerably.…”

“…It was reported that the temperature stability is improved with a reduction of shell thickness. In those previous studies, however, additional effects due to factors such as different chemistry in the shell [10,26,27] and difference in grain size [25,27] might have influenced the results. In addition, the variation of the core/shell fraction is estimated mostly by indirect methods, such as EDS [10,26,27] and synchrotron X-ray diffraction [25].…”

“…In previous investigations, the effects of the volumetric ratio of core/shell on dielectric-temperature behavior have been studied for samples with different ball milling time [6,25,26], thermal cycle [10] and sintering atmosphere [27]. It was reported that the temperature stability is improved with a reduction of shell thickness.…”

“…The effects of processing parameters, such as ball milling time [6,25,26], thermal cycle [10] and sintering atmosphere [27], on the microstructure and dielectric properties of BaTiO 3 systems have also been investigated in relation to the variation of the core/shell volumetric ratio. Wang et al [26] reported that in a (Mg,Y)-doped BaTiO 3 system, the shell thickness increases with a reduction of core size and the dielectric-temperature behavior is deteriorated as the ball milling time is increased.…”

Electrical and structural characterization of PTCR pure BaTiO3 nanopowders synthesized by sol–gel emulsion technique

“…As the endothermic peak is absent in the DSC curves of the present work, it is clear that the percentage tetragonality in the synthesized powders is below 64%. Though high-permittivity and reliability is associated with the tetragonal structure, the sharp transition of permittivity at T c restricts its application [40]. Highpermittivity and stable dielectric constant for a large temperature range is required of a BaTiO 3 ceramic capacitor [41].…”