Hiro Einishi

Growth of Epitaxial 100-Oriented KNbO3?NaNbO3 Solid Solution Films on (100)cSrRuO3?(100)SrTiO3 by Hydrothermal Method and Their Characterization

Films of solid solution in KNbO3–NaNbO3 (KNN) were deposited at 240 °C on (100)cSrRuO3∥(100)SrTiO3 substrates by the hydrothermal method. (KxNa1-x)NbO3 films with x = 0–1.0 were synthesized by changing the fraction of KOH in a solution of KOH and NaOH. The x in (KxNa1-x)NbO3 continuously changed with the volume fraction of KOH, while the deposition amount strongly depended on x. Epitaxial films with 100 orientation were obtained in the entire composition range and their out-of-plane lattice spacing changed with x. All the films showed ferroelectricity and their remanent polarization became larger than what above x = 0.58.

Crystal Structure Analysis of Hydrothermally Synthesized Epitaxial (KxNa1-x)NbO3 Films

Epitaxial (KxNa1-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 (KxNa1-x)NbO3 films consisted of a perovskite phase without any impurity phase. High-temperature XRD data showed that (KxNa1-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, (KxNa1-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 (KxNa1-x)NbO3 composition.

Growth of Orientation-Controlled Epitaxial KNbO3 Thin Film by Hydrothermal Method

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.

Effect of Deposition Time on Film Thickness and Their Properties for Hydrothermally-Grown Epitaxial KNbO3 Thick Films

Deposition behavior and the crystal structure of the epitaxial KNbO3 films, grown at 240 °C on (100)cSrRrO3∥(100)SrTiO3 substrates using hydrothermal method, as well as their ferroelectric and piezoelectric properties were systematically investigated. Film deposition was detected to have begun after 2 h from the start, and the thickness increased with increasing the deposition time up to 4 h, but contrary decreased after 9 h due to the etching by KOH. X-ray diffraction (XRD) patterns of the films were basically the same regardless of the deposition time. However, the films deposited for 15 h introduces large amount of voids than those for 2 h. Ferroelectric and piezoelectric response of the films deposited for 2 and 15 h were measured to have similar film thickness, but the maximum applied electric field for the 2-h films was twice as that for the 15-h ones. The prototype ultrasonic transducer was fabricated using the KNbO3 films, which were deposited by hydrothermal method at 240 °C for 3 h, and proved to be able to transmit and receive ultrasonic signals above 90 MHz in degassed water.