Polarization-Free Straining of Barium Titanate Single Crystals

Large strain actuation in (001)-oriented barium titanate (BaTiO₃) single crystals subjected to combined uniaxial stress and electric field is examined. The hysteresis evolution of the crystal under combined electromechanical loading reveals incomplete switching characteristics and a considerable disproportion of slope gradients at zero electric field for the measured polarization and strain hysteresis curves. A likely cause for the disproportion of slope gradients is the cooperative operation of multiple 90° switching systems by which “polarization-free” strain changes are induced. An in-situ domain observation study reveals the formation of bubble-like micro-domains prior to the macroscopic 90° switching of the crystal bulk. The presence of these bubble-like “switching weak points” indicates that regions within the crystal do not necessarily switch 90° at the same time, and hence, in a way, supports the existence of multiple 90° switching systems. The hysteresis evolution of the crystal is investigated again at 55 °C under identical electromechanical loading conditions. At a temperature higher than room temperature, the degree of discrepancy between the slope gradients at zero electric field for the measured polarization and strain hysteresis curves is significantly reduced. This is due to the increase in domain wall mobility, lowering the extent of incomplete switching at maximum electric field.