Electric-field-induced polarization and strain in 0.94(Bi1/2Na1/2)TiO3-0.06BaTiO(3) under uniaxial stress

Abstract

The strain and polarization hystereses of lead-free 0.94Bi(1/2)Na(1/2)TiO(3)-0.06BaTiO(3) during unipolar electric field loading are obtained from room temperature to 150 degrees 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 degrees C a large strain with a large-signal piezoelectric coefficient d(33)* 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 e(P) (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 eta* = w(w + e(P))(-1). It is found that eta* saturates at similar to 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.