Crystal Symmetry of BaTiO3 Grains in X7R Multilayer Ceramic Capacitors

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 ( pO(2)), is discussed.