Chemical Solution Deposition and Infrared Study of K(Ta,Nb)O 3 Thin Films

Potassium tantalum niobate (KTaxNb1-xO3, (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 substrates. A homogeneous and stable sol was obtained by dissolving potassium, niobium and tantalum isobutoxides in absolute isobutanol, refluxing for 30 min and adding diethanolamine as a modifier. The sol was deposited by spin coating. KTN perovskite films were successfully prepared only on substrates covered with Al2O3 "chemical" and KNbO3 seeding buffer layers, otherwise a pyrochlore structure was preferred. Annealing temperature and heating regime were also important factors for film quality. The powder X-ray diffraction confirmed that the prepared films had pseudocubic perovskite structure. The infrared transmittance spectrum of the films for high concentration of Ta shows three minima corresponding to optical active phonons in the perovskite crystal structure. Their positions are in agreement with those for the bulk material, except for the 14 cm(-1) shift of the lowest phonon, which has been also observed in other perovskite materials. The temperature dependence of the phonon parameters has also been studied, too.