Ferroelectric and piezoelectric properties of (K,Na)NbO₃ thick films prepared on metal substrates by hydrothermal method

(K_{0. 88}Na_{0. 12})NbO₃ (KNN) thick films with various thicknesses were prepared on Ni-based metal substrates by hydrothermal method. Although the deposition of KNN films was hardly observed directly on metal substrates until 12 h, the amount of KNN films deposited on both SrRuO₃/LaNiO₃- and SrRuO₃-covered Ni based metal substrates increased to about 5 μm with increasing deposition time above 3 h. X-ray diffraction studies confirmed the formation of {100}_c- and randomly-oriented KNN films on SrRuO₃/LaNiO₃- and SrRuO₃-covered metal substrates, respectively. Ferroelecctric property studies revealed an improved remanent polarization and an improved piezoelectric response of {100}_c-oriented KNN films over the randomly-oriented KNN films. In addition, the values for {100}_c-oriented KNN films were similar to those of {100}_c-oriented epitaxial KNN films prepared on (100)_cSrRuO₃//SrTiO₃ substrates.