Broadband viscoelastic spectroscopy measurement of mechanical loss and modulus of polycrystalline BaTiO₃ vs. temperature and frequency

Characterization of pure polycrystalline BaTiO 3 was carried out by means of Broadband Viscoelastic Spectroscopy (BVS) and Differential Scanning Calorimetry (DSC) above ambient temperature. A peak in mechanical loss has been observed near the Curie point 130 °C. The magnitude of the peak increases with thermal rate and decreases with frequency. Expressions for the peak magnitude have been derived based upon available models describing the first order phase transition. Mechanical anomalies were observed outside the vicinity of the phase transition. Transition temperature measured by BVS differed from that via DSC; the effect of stress on the ferroelastic transformation is a possible cause. Isothermal frequency scans revealed a hump in mechanical loss in the vicinity of the transition temperature below 1 Hz and a modulus decrease with decreasing frequency. Quasi‐isothermal studies revealed a significant softening in bulk modulus and a transient negative Poisson's ratio during the tetragonal‐to‐cubic phase transition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)