Structure property relationships in core-shell BaTiO₃–LiF ceramics

Abstract

A sintering, microstructural development and dielectric property study of BaTiO3–LiF ceramics was performed to assess the potential application of low-fired multilayer capacitors. Not only does LiF allow for sintering below 1000 °C, it also allows for the manipulation of dielectric properties and interfaces within BaTiO3–LiF ceramics. Using mixing laws, a model of the dielectric properties of the core-shell microstructures is presented that agrees well with the observed experimental data.

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

“…The addition of solute elements often results in the formation of an inhomogeneous microstructure during sintering that is typified by a core/shell structure [1][2][3][4][5][6][7]. A core/shell grain is a dual-phase grain that consists of a core phase at the center and a shell phase around the core.…”

“…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]. The improvement of the temperature-dependent behavior has been attributed to the contribution of the shell phase, which shows an appreciable displacement of the maximum dielectric constant down below room  temperature with a broadened transition peak, so-called diffuse phase transition (DPT) behavior, similar to that of relaxor materials [11][12][13][14].…”

“…The effects of various kinds and amounts of additives have been studied [2,4,5,9,10,[15][16][17][18][19][20][21][22], including in particular those of rare earth elements with intermediate ionic radii (Dy, Ho, Y and Er) [9,10,[19][20][21][22][23]. In the case of rare earth doping, high insulation resistance can be maintained for a long time, which enables the realization of thinner dielectric layers and extended life time in the use of MLCCs [24].…”

Design of a bilayer ceramic capacitor with low temperature coefficient of capacitance

“…[5][6][7][8][9][10] Limited diffusion of the dopants into BT grains leads to a concentration gradient of doped BT resulting in a "core-shell-like structure" (CS). 5,6,[11][12][13][14][15] This structure can be considered to be a core-region of undoped BT (Tc $ 120-130 C) surrounded by a shell-region of micro volumes of different dopant concentrations, leading to a spread of Curie temperatures. 12 This approach engineers CS microstructures with a broad permittivity-temperature profile, reducing TCC to the levels required for industry standard ratings.…”

“…5,6,[11][12][13][14][15] This structure can be considered to be a core-region of undoped BT (Tc $ 120-130 C) surrounded by a shell-region of micro volumes of different dopant concentrations, leading to a spread of Curie temperatures. 12 This approach engineers CS microstructures with a broad permittivity-temperature profile, reducing TCC to the levels required for industry standard ratings. Inducing a CS microstructure requires an iterative approach which is resource intensive.…”