Mechanical loss and Young's modulus associated with phase transitions in barium titanate based ceramics

The mechanical loss (Q(-1)) and Young's modulus (E) were measured as a function of temperature in the range 100 K < T < 450 K on rectangular plate specimens of BaTiO3 driven electrostatically in flexural vibration mode at resonance frequencies between 2-4 kHz. Q(-1)(T) and E(T) curves show the following three phase transitions in BaTiO3: rhombohedral to orthorhombic (T-R-O), orthorhombic to tetragonal (T-Q-T), and tetragonal to cubic (T-Curie). Each phase transition induces a very narrow mechanical loss peak of Q(-1) and a very sharp anomaly in the elastic modulus. Moreover, three other mechanical loss peaks are located below the phase transition temperatures in coarse grained specimens and these peaks seem to be associated with the motion of domain walls. These secondary peaks are not observed in fine grained undoped ceramics. The use of dopants such as Co or Nb produces an attenuation of the mechanical loss, a smoothing of elastic modulus anomalies, and a shifting of the phase transition temperatures.