MECHANICAL LOSS AND ELASTIC-MODULUS ASSOCIATED WITH PHASE-TRANSITIONSOF BARIUM-TITANATE CERAMICS

The internal friction (Q(-1)) and elastic modulus (E) were measured vs . temperature (100 < T < 450 K) for rectangular plate specimens of BaT iO3 driven electrostatically in flexural vibration at resonance freque ncies between 2 and 4 kHz. The Q(-1)(T) and E(T) curves exhibit the fo llowing three phase transitions in BaTiO3: rhombohedral to orthorhombi c (T-R-O), orthorhombic to tetragonal (T-O-T) and tetragonal to cubic (T-Curie). Each phase transition induces either a very narrow internal friction peak or a discontinuous change in Q(-1) and a very sharp ano maly of the elastic modulus. Moreover, two other internal friction pea ks are located below the phase transition temperature. These peaks see m to be associated with the motion of domain walls. The secondary peak s are not observed on undoped ceramics sintered at low temperature. Th e influence of dopants such as Nb and Co results in the attenuation of internal friction and the smoothing of elastic modulus anomalies.