Deposition of orientation-controlled thick (K,Na)NbO₃ films on metal substrates by repeated hydrothermal deposition technique

(K,Na)NbO₃ thick films were grown at 240°C on Ni-based metal substrates by repeated hydrothermal method. The metal substrates were covered with two types of buffer layers; SrRuO₃/LaNiO₃ and SrRuO₃. Film thickness monotonically increased with increasing number of deposition cycles. The 27 ¯m-thick film was obtained on the metal substrate with SrRuO₃/LaNiO₃ by four cycles. The obtained films tended to show {100}_c orientation and their degree of orientation increased with increasing number of deposition cycles. Films deposited on SrRuO₃/LaNiO₃-covered metal substrates showed more highly {100}_c orientation compared with those on SrRuO₃-covered metal substrates. Remnant polarization and coercive field measured at 5 kHz were 12 ¯C/cm² and 70 kV/cm, while their effective values of piezoelectric coefficient (d₃₃) was 3540 pm/V for both films. These properties remained unchanged irrespective of a number of deposition cycles despite the orientation change of films. These results show that repeated hydrothermal deposition technique is one of the effective ways to prepare thick (K,Na)NbO₃ films on metal substrates.