Manufacturing MLCCs consisting of f

Manufacturing MLCCs consisting of ferroelectric ultrafine or even nanocrystalline grains, however, still remain challenging, because the polarity and herewith the dielectric constant of BaTiO3 generally deteriorates with decreasing grain-size, a phenomenon which is commonly referred to as “size-effect”. It is often reported that downsizing the crystals dimensions of BaTiO3-grains below a critical value results in the stabilization of the paraelectric and crystallographically centrosymmetric cubic, high-temperature polymorph of the perovskite lattice at the expense of the tetragonal structure, even at room temperature.5,6 This leads in average to a reduction of the tetragonal distortion of the lattice and a decrease of the herewith connected ferroelectric polarization. Arlt et al. showed that for BaTiO3 maximum values of permittivity around 5000 can be achieved at grain sizes of 0.8–1um.7 Similarly, Hirata et al. reported later that the dielectric constant showed a slightly higher maximum of 5700 at a grain size of approximately 1.4um.8 In any case, however, a marked decrease of the relative dielectric constant with diminishing grain-size is observed. Contrary to this, Guillemet-Fritsch et al. reported recently that ultrafine La-doped BaTiO3 ceramics with an average grain size of only 250–300 nm unexpectedly show colossal permittivity values up to 106.9