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(KxNa1−x)NbO3 films were deposited on Nb-doped (100)SrTiO3 substrates at 240 °C for times between 1 and 6 h by a hydrothermal method. Over this time series, the measured (K + Na)/Nb ratio of the films was found to remain constant, but the bulk K/(K + Na) ratio, x, decreased from an initial value of 0.75–0.56. It was determined that film growth initially proceeded through crystallization of the K-rich phase (K0.75Na0.25)NbO3. For film growth times greater than 3 h, a second perovskite phase with a smaller unit cell volume was detected, with an estimated composition of (K0.36Na0.64)NbO3. As such, the measured bulk composition value x = 0.56 was determined to be the result of a combination of these two phases, as opposed to originating from a single phase. Cross-sectional transmission electron microscopy analyses of films prepared for 6 h revealed that they consist of two layers in the direction normal to the substrate; this bilayer-type structure, only observed for hydrothermal growth of this material, is considered to arise from the large solubility mismatch between the Nb precursor and KOH and NaOH in the growth solution.
Epitaxaially-grown KNbO3 thick films over 8 μm in thickness were successfully grown at 220 °C for 6 h on (100)cSrRuO3//SrTiO3 substrates by a hydrothermal method. Epitaxial SrRuO3 layers grown on (100)cSrTiO3 substrates by sputter method were used as bottom electrode layers. Relative dielectric constant and the dielectric loss were 530 and 0.11, respectively. Clear hysteresis loops originated to the ferreoelectricity were observed and a remanent polarization was 25 μC/cm2 at a maximum applied electric field of 540 kV/cm. In addition, the hydrothermal KNbO3 thick film was able to transmitting and receiving of ultrasonic waves over 50MHz.
We have studied on hydro-thermally synthesis of Pb(Ti, Zr)O3(PZT)piezoelectric polycrystalline thick film on titanium (Ti) substrate. The purpose of this study is resolving the problems for application of PZT hydrothermal polycrystalline thick film to the ultra miniature high frequency medical ultrasound array probe. The problems were the existence of pinholes in the deposited PZT film, the rough surface of that, low dielectric breakdown electric field etc. The surface of Ti substrate was pretreated to have hydrophilic property by using high reactivity of hydrogen peroxide for resolving the problems in this study. As results, hydrophilic property on the surface of Ti substrate was improved. Surface of PZT hydrothermal polycrystalline thick film without pinholes and smooth surface of that were obtained. Furthermore, the material properties like density, Young's modulus and piezoelectric constant d31 were increased by the pretreatment of Ti substrate. Consequently, dielectric breakdown electric field of PZT hydrothermal polycrystalline film was improved.
The purpose of this study was to improve deposition rate of the hydrothermal method for lead zirconate titanate (PZT) thick film on titanium substrate. We developed a high-speed rotaion substrate holder at a tangential velocity of about 0.8m/s in autoclave. A titanium substrate was fixed by the holder on the surface of a stirring bar. For the film deposition, powder of TiO2 was used instead of the liquid TiCl4. The deposition rate on titanium substrate was improved up to 7μm/24h. Piezoelectric constant d31 of the hydrothermal PZT film was -2.6 × 1011 V/m. This result was lower than that of PZT ceramics. However, this hydrothermal method obtained thick film and this film was confirmed to be polycrystalline PZT analyses of XRD and SEM. In addition, performance of thickness mode vibration of hydrothermal PZT 50μm thick film was investigated by radiating in water. The phase velocity of dilatational wave of the thickness mode vibration of the hydrothermal PZT film was 1800m/s and the electromechanical coupling factor was 47%.
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