Growth of epitaxial (K, Na)NbO3 films with various orientations by hydrothermal method and their properties

Abstract

{100}c-, {110}c- and {111}c-oriented epitaxial (K, Na)NbO3 thin films were grown at 240 °C on (100)cSrRuO3//(100)SrTiO3, (110)cSrRuO3//(110)SrTiO3, and (111)cSrRuO3//(111)SrTiO3 substrates by the hydrothermal method. Their film thicknesses increased with the deposition time and then eventually saturated at longer deposition times. Their saturated film thicknesses were mainly determined by their orientation and the order was {100}c-, {110}c- and {111}c-orientation regardless of any experimental conditions. These films consisted of grains with characteristic morphologies. All of the films exhibited similar ferroelectric and piezoelectric properties irrespective of the film orientation. The remnant polarizations (Pr) and coercive fields (Ec) of the {100}c-, {110}c- and {111}c-oriented films at the maximum electric field of 500 kV cm−1 were 31 μC cm−2 and 111 kV cm−1, 27 μC cm−2 and 94 kV cm−1, and 25 μC cm−2 and 110 kV cm−1, respectively, while their effective values of piezoelectric coefficient (d33) were approximately 31–33 pm V−1. Similar films are associated with its mixed domain structure.