Lead‐Free Ferroelectric Potassium Sodium Niobate Thin Films from Solution: Composition and Structure

Abstract

Lead‐free potassium sodium niobate ( K 0.5 Na 0.5 ) NbO 3 thin films on Pt (111)/ TiO 2 / SiO 2 / Si substrates have been prepared from the acetate–alkoxide‐based precursor solutions with the stoichiometric composition and with 5 or 10 mol% excess of sodium or potassium acetate. Upon heating to 750°C, the films crystallize in pure perovskite phase. The increasing amount of alkali excess in solutions increases the degree of {100} orientation and it influences the nucleation and growth processes in the films. The microstructure of about 250 nm thick films prepared from the stoichiometric and 5 mol% excess solutions consists of equiaxed grains of about 50 nm across, whereas the grain size in the about 220 nm thick films prepared from the 10 mol% excess solutions is about 200 nm. The energy dispersive X‐ray spectroscopy revealed that the alkali excess in precursor solutions contributed to a higher level of chemical homogeneity of the films on the micrometer scale. The chemical composition of the films prepared from the 5% potassium‐excess solution was closest to the ( K 0.5 Na 0.5 ) NbO 3 composition among all the samples as a result of more pronounced potassium losses upon heating. These films had the room temperature values of dielectric permittivity, dielectric losses, remnant polarization, and coercive field measured at 1 kHz 610, 0.015, 8 μC/cm 2 , and 80 kV/cm, respectively.