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

Using a modified Landau-Devonshire type thermodynamic potential, we show that dielectric tunability eta of a tetragonal ferroelectric film can be analytically solved. At a given electric field E, eta is a function of the remnant polarization (P,,) and the small-field relative dielectric permittivity (chi(F)(0)), which are commonly measured material properties. After a survey of materials, a large eta similar to 80% is predicted to be achievable in a (001)-oriented tetragonal (K-0.5,Na-0.5)NbO3 film. This strain-stabilized tetragonal phase is verified by density functional theory (DFT) calculations. (K-0.5,Na-0.5)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)(-0.21Cm(-2)) and a large chi(F)(0)(similar to 830-860), as well as a large eta close to the theoretical value. The measured dielectric tunabilities as functions of E are well described by the theoretical eta(E) curves, validating our integrated approach rooted in a theoretical understanding.

Automated summary

By utilizing a modified Landau-Devonshire thermodynamic potential, the dielectric tunability of tetragonal ferroelectric films was analytically solved, predicting a high tunability of 80%. This predicted performance was successfully validated through density functional theory calculations, with epitaxial films showing favorable properties in experimental measurements.