Microstructure of KTaxNb1−xO3 Thin Films on MgO (100) Single Crystals

Abstract

Thin KTaxNb1−xO3 (KTN) films were prepared by deposition of sol–gel precursor solutions on MgO (100) single crystals. Crystal structure and microstructure of the films as a function of processing parameters, such as rate, duration, and temperature of postdeposition heat treatment, were studied. Several techniques such as X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to analyze the films. It was observed that slow heating of KTN films promotes pyrochlore formation while fast‐firing of the films results in predominant formation of the perovskioe phase. In slow‐heated samples, TEM showed randomly oriented pyrochlore crystallites with a vermicular nanostructure of 10–30 nm with an interpenetrating porosity of the same range. In fast‐fired samples, large perovskite pockets with pyrochlore crystallites scattered among them were seen. The large perovskite grains were on the order of 0.1–0.5 μm, irregular in shape and porous. Transmission electron diffraction indicated these were single crystals, and ferroelectric domains were observed in them. Films of up to 1 μm thick were obtained by multiple deposition of the sol–gel KTN. Dense films were achieved when each layer was densified at 750°C for 2 h before the next layer was deposited.