Critical mechanical and electrical transition behavior of BaTiO₃: The observation of mechanical double loop behavior

Strain response of polycrystalline barium titanate (BaTiO₃) was investigated under high unipolar electric field (0 to 4 kV/mm) and compressive stress (0 to 400 MPa) in the temperature range from 25 to 160 °C. In the vicinity of the Curie point (T_C), nonlinear and hysteretic strain-electric field and strain-stress constitutive behaviors were observed, persisting above T_C where they correspond to the well-known electric field induced double loop polarization behavior. Analogous to the electrical double loops, the mechanical (strain-stress) hysteretic behavior above T_C is caused by a stress induced phase transition from the paraelectric/paraelastic to ferroelectric/ferroelastic phase; the electro-elastic (strain-electric field) hysteresis is similarly caused by an electric field induced phase transition. The stress and electric field at which transitions occur increase linearly with increasing temperature, exhibiting critical behavior typical for the first order phase transitions. The temperature limit for the induced phase transition extends up to 12 °C over T_C. Results are discussed in relation to the Landau-Ginzburg-Devonshire free energy expansion.