Large transverse piezoelectric properties of lead-free Bi0.5(Na0.82K0.18)0.5TiO3 films

The ferroelectric and piezoelectric properties of Bi0.5(Na1-xKx)0.5TiO3 (x = 0, 0.18 and 0.25) films deposited on Pt(111)/TiO2/SiO2/Si(100) substrates using a chemical solution deposition technique were examined as part of an ongoing study into the development of lead-free piezoelectric films. The effective transverse piezoelectric coefficient (e∗31,f) was examined to assess the potential applications of these piezoelectric films for device applications using the Bi0.5(Na0.82K0.18)0.5TiO3 (BNKT18) cantilever, which is the morphotropic phase boundary composition in the Bi0.5(Na1-xKx)0.5TiO3 system. The BNKT18 cantilever showed good linearity of piezoelectric displacement with low hysteresis under an applied field, and exhibited a high effective transverse piezoelectric coefficient (e∗31,f) of ∼5.15 C/m2 and a figure of merit ((e∗31,f)2/ε0εr) of 3.8 GPa, which are comparable to the preferred oriented lead-free piezoelectric and lead zirconate titanate thin films. This suggests that the BNKT18 film is a potential candidate for lead-free piezoelectric film devices.