Processes and interface structures accurring during BaTiO₃ sintering in the presence of the sintering aid SiO₂ are studied by model experiments. The formation of fresnoite Ba₂TiSi₂O₈ and different Ti-rich barium titanates by solid state reactions proceeding at the (001)BaTiO₃/SiO₂ interface is followed by XRD and TEM. High resolution transmission electron microscopy (HRTEM) permits the structure to be studied of the various solid-solid reaction fronts involved. The observations indicate e.g., a certain topotaxial reaction mechanism at the Ba₄Ti₁₃O₃₀/BaTiO₃(001) and Ba₆Ti₁₇O₄₀/BaTiO₃(001) reaction fronts, which comprises the outdiffusion of barium, the indiffusion of titanium and oxygen, and a restacking of the BaTiO₃001planes.

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