Phase transition and high dielectric constant of bulk dense nanograin barium titanate ceramics

Barium titanate (BTO) ceramics with an average grain size of 8nm were fabricated and studied. The temperature dependent Raman spectra revealed successive transitions from rhombohedral to orthorhombic, tetragonal, and cubic as the temperature increased from 87to673K. Local piezoresponse force measurements indicated that the ceramics had switchable polarization at room temperature. Dielectric measurements showed a broad ferroelectric-to-paraelectric phase transition with a maximum permittivity of 1800 at 390K. All these results suggest that ferroelectricity could remain in BTO ceramics with grain size as small as 8nm in diameter.