Analysis on the Sintering Process of X7R MLCC Materials

Abstract

SYNOPSIS Transmission Electron Microscopy and Scanning Transmission Electron Microscopy were applied to study sintering process of the X7R MLCC materials, BaTiO3-MgO-Y2O3-(BaCa)SiO3. Though the materials were porous at the intermediate state of sintering process, the Ar-ion beam milling technique was employed for specimen preparation of electron microscopy. Succeeding in preparation, structural changes in microscopic scale have become visible. It has found that at rather low firing temperatures where the materials would not show any shrinkage in the macroscopic scale, the additives such as yttria, were already active. It was confirmed that thin Y layers of a few nanometers in thickness were formed at the surface of BaTiO3 Particles. The macroscopic shrinkage could progress , as yttria or calcia begins to diffuse toward the inner part of BaTiO3 particles. After the shrinkage, so-called core-shell structures could be observed.

Role of yttrium and magnesium in the formation of core-shell structure of BaTiO3 grains in MLCC

“…8,9 In case of BT-MgO-Y 2 O 3 system, Fujikawa et al reported that Y dissolved in BT at 1200 • C followed by Ca incorporation into shell. 10 And, several different elements such as Zr, Yb, Sr, and Y have been reported as an element to form a shell. 11,12 In spite of the various studies, it is still unclear which element between rare earth and Mg plays a predominant role in forming a shell and what the formation mechanism of the shell is.…”

Doping behaviors of dysprosium, yttrium and holmium in BaTiO3 ceramics

“…The shell is known to have non-ferroelectric pseudo-cubic structure, whereas the core is pure BT with a ferroelectric tetragonal structure. [1][2][3] It is reported that a rare-earth element is a dominant additive in forming a shell and the core-shell structure is well developed when the rare-earth element and magnesium are added to BT. 4 Rare-earth elements are known to exhibit useful functions of stabilizing the temperature dependence of relative dielectric constant and lowering the dissipation factor in dielectric ceramics.…”

The Influence of BaTiO₃ Tetragonality by Solid State Synthesis on MLCC’s Dielectric Characteristics

“…The structure which Rare-earth element such as Y is located around grains of dielectrics is called core-shell structure. And it is said that core-shell structure makes temperature characteristics of relative dielectric constants flat [3][4][5].…”