Hysteresis behaviors of barium titanate single crystals based on the operation of multiple 90o switching systems

Large strain actuation in barium titanate (BaTiO3) single crystals subjected to combined uniaxial stress and electric field is examined. A maximum strain of about 0.45% is measured under a combined loading of 2.7 MPa compressive stress and ±1.25 MV m-1 cyclic electric field. Above 2.7 MPa, the crystal does not cycle fully between the in-plane and out-of-plane polarized states due to large compressive stress, and consequently, a considerable reduction in actuation strain is apparent. 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 90o 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 90o switching of the crystal bulk. The presence of these bubble-like 'switching weak points' indicates that regions within the BaTiO3 single crystal do not necessarily switch 90o at the same time, and hence, in a way, supports the existence of multiple 90o switching systems. Results obtained in the present study are expected to assist the development of reliable constitutive models for single crystal ferroelectrics.