High electromechanical strain and enhanced temperature characteristics in lead-free (Na,Bi)TiO 3 –BaTiO 3 thin films on Si substrates

Here, we demonstrate the high electromechanical strain and enhanced temperature characteristics in the c-axis-oriented lead-free (Na,Bi)TiO3–BaTiO3 (NBT–BT) polycrystalline thin film prepared on Si substrates by rf magnetron sputtering. The effective transverse piezoelectric coefficient, e31*, estimated from the electromechanical strain measured under high electric field, reaches a high level of −12.5 C/m2, and is comparable to those of conventional Pb(Zr,Ti)O3 films. In-situ X-ray diffraction measurement and electron diffraction analysis revealed the electromechanical strain of the NBT–BT film to originate predominantly in elongation of the tetragonal (P4bm) crystal lattice in the c-axis direction. In addition to the large e31*, the NBT–BT film exhibits enhanced permittivity maximum temperature, Tm, of ~400 °C and no depolarization below Tm, as compared to bulk NBT–BT having Tm ≈ 300 °C and a depolarization temperature of ~100 °C. We conclude that the enhancement of temperature characteristics is associated with the distorted P4bm crystal lattice formed by deposition-induced stress and defects. We believe that the present study paves the way for practical applications of lead-free piezoelectric thin films in electromechanical devices.