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Epitaxial (K x Na1-x )NbO3 films with various compositions x were deposited on Nb-doped (100)SrTiO3 single crystal substrates at 240 °C by the hydrothermal method. Detailed crystal structures were analyzed by X-ray diffraction. All the (K x Na1-x )NbO3 films consisted of a perovskite phase without any impurity phase. High-temperature XRD data showed that (K x Na1-x )NbO3 films with x = 0.03 and 0.86 transformed to a single cubic phase at 600 °C through the intermediate phase. On the other hand, (K x Na1-x )NbO3 films with x = 0.24 showed two diffraction peaks at 600 °C originating from individual phases having different unit cell volumes. The result shows that these films consisted of a mixture of two perovskite phases with K- and Na- rich (K x Na1-x )NbO3 composition.

Epitaxial (K x Na 1¹x )NbO 3 films with 3¯m in thickness were deposited at 240°C on (100) c SrRuO 3 //(100)SrTiO 3 substrates by hydrothermal method. XRD patterns and Raman spectra were systematically changed with increasing x values. XRD patterns and Raman spectra was not dramatically changed by the annealing treatment at 600°C for 10 min under O 2 atmosphere. On the other hand, the electrical and piezoelectric properties were improved by this annealing treatment; leakage current density was diminished and longitudinal piezoelectric response was increased to 69 pm/V at x = 0.51.

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KNbO3 thin films were deposited at 240 oC on various kinds of single crystal substrates by hydrothermal method using aqueous solutions containing Nb2O5 and KOH. The deposition amount of the films was found not to be much dependent on the orientation and the surface roughness of the substrates, but on the electrical conductivity of the substrate. Epitaxial {100}, {110} and {111}-oriented KNbO3 films with ferroelectricity were grown on (100)c, (110)c, and (111)c -oriented SrRuO3//(100)SrTiO3 substrates, respectively.