Achieving a high dielectric tunability in strain-engineered tetragonal K0.5Na0.5NbO3 films

Abstract

Abstract Using a modified Landau-Devonshire type thermodynamic potential, we show that dielectric tunability η of a tetragonal ferroelectric film can be analytically solved. At a given electric field E, η is a function of the remnant polarization ( $$P_0^f$$ P 0 f ) and the small-field relative dielectric permittivity ( $$\chi _0^f$$ χ 0 f ), which are commonly measured material properties. After a survey of materials, a large η~80% is predicted to be achievable in a (001)-oriented tetragonal (K0.5,Na0.5)NbO3 film. This strain-stabilized tetragonal phase is verified by density functional theory (DFT) calculations. (K0.5,Na0.5)NbO3 films based on this design were successfully prepared via a sputtering deposition process on SrRuO3-buffered (100)SrTiO3 substrates. The resulted epitaxial films showed a sizable $$P_0^f$$ P 0 f (~0.21C m−2) and a large $$\chi _0^f$$ χ 0 f (~830–860), as well as a large η close to the theoretical value. The measured dielectric tunabilities as functions of E are well described by the theoretical η(E) curves, validating our integrated approach rooted in a theoretical understanding.