Electric-field-induced polarization and strain in 0.94(Bi1/2Na1/2)TiO3–0.06BaTiO3 under uniaxial stress

The strain and polarization hystereses of lead-free 0.94Bi1/2Na1/2TiO3–0.06BaTiO3 during unipolar electric field loading are obtained from room temperature to 150 °C under uniaxial compressive stress up to 446 MPa. At intermediate temperatures a stress-dependent peak evolves in both the maximum strain and polarization. At 125 °C a large strain with a large-signal piezoelectric coefficient d33∗ of 884 pm V−1 is observed, which decays upon the application of stress. This behavior is rationalized with a change in the primary strain mechanism from domain switching at low temperatures to a reversible electric field-induced transition from an ergodic relaxor state to a long-range order at high temperatures. Moreover, the energy terms w (the output mechanical work) and eP (the charged electrical energy density) that are related to the deformation and the polarization, respectively, are analyzed and used to define a large-signal efficiency η* = w(w + eP)−1. It is found that η* saturates at ∼150 MPa but decreases with increasing temperature and electric field. It is furthermore observed that notable strains are achieved at stress levels even far beyond the quasi-statically determined blocking force. Therefore, it is proposed that the presented testing procedure is suited to assess the dynamic actuatoric performance of a piezoceramic.