Phase Mixture and Reliability of BaTiO3-Based X7R Multilayer Ceramic Capacitors: X-Ray Diffractometry and Raman Spectroscopy

Abstract

BaTiO3-based multilayer ceramic capacitors (MLCCs) using Ni base-metal electrodes (BME) exhibiting EIA-X7R dielectric behavior are represented by the characteristic microstructure of core–shell grains. In the present study, the crystalline phase contents in the mixture were determined quantitatively for two groups of experimental BME-MLCCs, one with CaO doping and the other with (CaO+MgO) codoping by Rietveld refinement using the software package TOPAS®. X-ray diffractometry was used for the identification of crystalline phases whose quantities were determined for cubic (C), tetragonal (T), and rhombohedral (R)–BaTiO3. Phase identification was corroborated by Raman spectroscopy where the characteristic phonon vibration modes corresponding to the C-, T-, and R-phase were assigned. It is suggested that the C-phase content, corresponding to the shell grains containing intragranular voids and the shell region of the core–shell grains, and the R-phase content, corresponding to the modulated core region, not only determine the diffusiveness of the temperature coefficient of capacitance curve but also serve as measuring indices for evaluating the resistance of MLCC formulations against dc degradation.