The microstructure of multilayer ceramic capacitors (MLCC) based on BaTiO3 and nickel electrode, have been analyzed using the scanning and the transmission electron microscopy. In order to investigate how MgO improves MLCC against dc degradation, both CaO doped and (CaO+MgO) codoped chips, pristine as well as highly accelerated life‐tested, are studied. BaTiO3 grains are characterized by both the types I and II core shell structure, which is typical of MLCC exhibiting the X7R dielectric behavior. Intragranular voids are found in BaTiO3 grains in the vicinity of the electrode–dielectric interface. Void‐containing grains are more frequently observed and voids are more abundant in (CaO+MgO) codoped chips than in CaO doped ones. Higher concentration of oxygen vacancies is induced extrinsically from both MgO codoping and Ni diffusion into BaTiO3 grains along the electrode–dielectric interface during sintering. Such oxygen vacancies have reacted with both cation vacancies and by an inverse Schottky defect reaction and condensed to form voids. This reaction requiring cation and oxygen vacancies in the stoichiometric BaTiO3 composition of 1:1:3 has significantly decreased the randomly distributed mobile oxygen vacancies, and contributes to improve against dc degradation.

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.

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Convergent beam electron diffraction combined with conventional transmission electron microscopy is used to determine the crystal symmetry, and with energy‐dispersive spectrometry (EDS) the microchemistry of BaTiO3 grains in (CaO+MgO)‐codoped, EIA‐X7R multilayer ceramic capacitors (MLCCs). The point group symmetries of the core–shell grain and the shell grain in MLCCs are analyzed following the procedures reported by Buxton and colleagues. It is found that the point group symmetry of the core region from the type‐I and type‐II core–shell grains are tetragonal (T ) 4mm and rhombohedral (R) 3m, respectively, with that of the shell region and the shell grain is the cubic (C ) m3m. The dependence of the C‐, T‐, and R‐phases on the oxygen vacancy concentration generated by acceptor dopants, sintered in low oxygen partial pressure ( pO2), is discussed.