INTERNAL-FRICTION STUDY OF TRANSFORMATION DYNAMICS IN BATIO3 CERAMICS

The internal friction (IF) and relative change of modulus of a doped semiconducting polycrystalline BaTiO3 sample were measured by an inverted torsion pendulum with forced oscillation as the sample was heated in vacuum from -150 degrees C to 100 degrees C. Two IF peaks, P-1 and P-2 and two modulus, minima C-3v/C-2v and C-2v/C-4v, were observed corresponding to two phase transformations. All the IF peaks exhibit the characteristics of the first-order phase transformations. Each peak temperature is independent of frequency and the peak height increases with an increasing value of (T/omega)(n). A coupling coefficient of the phase interface to the oscillating stress is found to be alpha(omega)=alpha'omega(-1). For the two peaks P-1 and P-2 in the doped BaTiO3 specimen, the values of n and l have been determined to be n(1)=0.225, n(2)=0.190, l(1)=0.101, l(2)=0.204. Our study indicates that the IF arises from the motion of phase interfaces during the process of the first-order phase transformation. A dynamic interaction model is proposed to explain the special features of IF during the two phase transformations.