The effect of surface termination on dielectric nonlinearity in potassium sodium niobate thin films

Abstract The impact of alkali‐rich and alkali‐depleted surface terminations on dielectric nonlinearity and ferroelectric properties was investigated in sputtered K 0.5 Na 0.5 NbO 3 (KNN) films. For the alkali depleted surface termination, a ∼3 nm thick amorphous interfacial layer was found near the top electrode. The presence of a non‐ferroelectric interfacial layer reduces both the net remanent ( P r ) and maximum polarization ( P max ) while increasing the coercive field ( E c ) in the KNN films. P max decreased from 31.5 to 30.3 µC/cm 2 , likely due to the reduced electric field in the bulk of the film. The influence of the interfacial layer on dielectric properties was evaluated using a capacitor in series model. After removing the effects of the interfacial layer, the Rayleigh coefficients ε init and α increased by 11 and 47%, respectively. The interfacial layer has more impact on irreversible domain wall motion than on reversible contributions to the relative permittivity. It is believed that this occurs because a higher concentration of defects, such as or , associated with the alkali‐depleted interfacial layer generates internal fields that pin domain walls. Alkali depleted surface terminations also produce a higher pseudo‐activation energy for polarization reversal compared to films with alkali rich terminations, with deeper potential wells in the material's energy landscape.