CSD ceramic K(Ta,Nb)O$_{3}$ thin films and their characterization by infrared spectroscopy

Potassium tantalate niobate (KTa$_{\rm x}$Nb$_{1\hbox{\scriptsize{-}}{\rm x}}$O$_{3}$, (KTN), where x = 0, 0.21, 0.36, 0.53, 0.74, 0.82, 0.86, and 1) thin films were prepared by chemical solution deposition (CSD) on Si (100) substrates. A homogeneous and stable sol was obtained by dissolving potassium, niobium and tantalum isobutoxides in absolute isobutanol, refluxing for 30min and adding diethanolamine as a modifier. The sol was deposited by spin coating. KTN perovskite films were successfully prepared only on substrates covered with Al$_{2}$O$_{3}$ “chemical” and KNbO$_{3}$ seeding buffer layers, in other cases pyrochlore structure was preferred. Annealing temperature and heating regime were also important factors for film quality. The optimum final annealing temperature was 750$^{\circ}$C/5min. It was confirmed by powder X-ray diffraction that the prepared films have pseudocubic perovskite structure. The infrared transmittance spectra have been measured in the temperature range from 10 to 300 K. For varying Ta/Nb ratio, the transmittance shows a continuous transformation from KT to KN. The spectra of the films for high concentration of Ta are dominated by three minima corresponding to optical active phonons in the perovskite crystal structure. Their positions are in agreement with the bulk material, except the 14 cm$^{\hbox{\scriptsize{-}}1}$ shift of the lowest phonon, which has been also observed in other perovskite materials. For the Nb rich film a new band appears at 300 cm$^{\hbox{\scriptsize{-}}1}$. Its position is close to the frequency of A$_{1}$ mode of tetragonal KNbO$_{3}$. The spectra were fitted by the model of damped harmonic oscillators and the temperature dependence of the phonon parameters has been studied, too