Insights into high electric-field-induced strain in BiAlO3 modified Bi1/2Na1/2TiO3 films

Abstract

The advancement of high-strain piezoelectric materials has presented a longstanding challenge, particularly in the development of high-strain polycrystalline lead-free piezoelectric thin films. In this work, we present a strategy for customizing the electrostrain in lead-free thin films through phase transition engineering. Herein, we achieved a high recoverable electrostrain in Bi1/2Na1/2TiO3-BiAlO3 (BNT-BA) film. To accomplish this, the ferroelectric BNT and BNT-BA films with identical thicknesses of 500 nm were fabricated on Pt(111)/TiO2/SiO2/Si(100) substrates using a sol-gel method. Compared to BNT film, BNT-BA film exhibited higher polarization response and superior field strength endurance maintaining the energy storage density beyond the breakdown field strength of BNT. The BNT-BA film demonstrated a large unipolar strain of S = 0.43% with a normalized strain (Smax/Emax) of 203 pm/V, followed by an effective transverse piezoelectric coefficient () of ~2.48 C/m2, which was more than two times larger than the value obtained for BNT (i.e., Smax/Emax = 72 pm/V, and of ~1.09 C/m2). Such a high strain response in BNT-BA film would be attributed to the electric-field-induced phase transition of the mixed (i.e., cubic and rhombohedral) phases into rhombohedral and tetragonal phases (mainly the rhombohedral structure) and recovered back to the original state when the electric field was removed. These findings would suggest new pathways for achieving significant strain levels via alternative mechanisms, potentially enhancing the effectiveness and expanding the applications of piezoelectric materials.