Piezoelectric Properties of Lead-Free (Na,Bi)TiO3--BaTiO3 (001) Epitaxial Thin Films around the Morphotropic Phase Boundary

The piezoelectric properties and the crystallographic nature of ($1-x$)(Na,Bi)TiO 3 --$x$BaTiO 3 (NBT--BT) thin films around the morphotropic phase boundary (MPB) composition ($x=0.05{\mbox{--}}0.10$) were studied. NBT--BT thin films were grown epitaxially on Pt(100)/MgO(100) substrates by RF magnetron sputtering and exhibited highly (001)-oriented single-phase perovskite with a tetragonal structure. A maximum piezoelectric coefficient $e_{31}$ of $-14.4$ C/m 2 was obtained at the $x = 0.07$ composition of the tetragonal side near MPB ($x = 0.06$). These results indicate that NBT--BT thin films around the MPB are a promising lead-free replacement for Pb(Zr,Ti)O 3 (PZT) based applications.