@article{9878, abstract = {{(K,Na)NbO3 ceramics have attracted much attention as lead-free piezoelectric materials with high piezoelectric properties. High-quality (K,Na)NbO3 ceramics can be sintered using KNbO3 and NaNbO3 powders synthesized by a hydrothermal method. In this study, to enhance the quality factor of the ceramics, high-power ultrasonic irradiation was employed during the hydrothermal method, which led to a reduction in the particle size of the resultant powders.}}, author = {{Isobe, G. and Maeda, Takafumi and Bornmann, Peter and Hemsel, Tobias and Morita, Takeshi}}, issn = {{0885-3010}}, journal = {{Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on}}, keywords = {{Q-factor, ceramics, crystal growth from solution, particle size, piezoelectric materials, potassium compounds, powders, sintering, sodium compounds, ultrasonic effects, (K0.48Na0.52)NbO3, KNbO3 powders, NaNbO3 powders, high-power ultrasonic irradiation, lead-free piezoelectric materials, lead-free piezoelectric powders, particle size reduction, piezoelectric properties, quality factor, sintered (K0.48Na0.52)NbO3 ceramics, sintering, ultrasonic-assisted hydrothermal method, Acoustics, Ceramics, Lead, Piezoelectric materials, Powders, Radiation effects, Transducers}}, number = {{2}}, pages = {{225--230}}, title = {{{Synthesis of lead-free piezoelectric powders by ultrasonic-assisted hydrothermal method and properties of sintered (K0.48Na0.52)NBO3 ceramics}}}, doi = {{10.1109/TUFFC.2014.6722608}}, volume = {{61}}, year = {{2014}}, } @inproceedings{9788, abstract = {{A hydrothermal method utilizes a crystallization process in the solution so that the pure and high-quality powders can be realized. Sintering from the hydrothermal KNbO3 and NaNbO3 powders, a high-dense lead-free piezoelectric (K,Na)NbO3 ceramics could be obtained (density: 98.8\%). Concerning about the g33 constant, high value as large as commercial PZT ceramics was measured. Therefore, the hydrothermal (K,Na)NbO3 ceramics is usable for the sensors and the energy harvesting devices. To demonstrate the (K,Na)NbO3 ceramics, a hydrophone sensor was fabricated and evaluated.}}, author = {{Maeda, Takafumi and Bornmann, Peter and Hemsel, Tobias and Morita, Takeshi}}, booktitle = {{Ultrasonics Symposium (IUS), 2012 IEEE International}}, issn = {{1948-5719}}, keywords = {{crystallisation, hydrophones, piezoceramics, potassium compounds, powder technology, powders, sensors, sintering, sodium compounds, (K0.48Na0.52)NbO3, KNbO3 powder, NaNbO3 powder, crystallization, energy harvesting devices, g33 constant, hydrophone sensor, hydrothermal lead-free (K0.48Na0.52)NbO3 ceramics, hydrothermal method, piezoelectric applications, sintering, Materials, Transducers}}, pages = {{194--195}}, title = {{{Piezoelectric applications of hydrothermal lead-free (K0.48Na0.52)NbO3 ceramics}}}, doi = {{10.1109/ULTSYM.2012.0048}}, year = {{2012}}, } @article{9743, abstract = {{The hydrothermal method enables the production of high-quality piezoelectric materials. In this study, we propose to irradiate the reaction solutions with ultrasonic power during the hydrothermal method to obtain a shorter reaction time and a smooth film surface. A high-pressure reaction container for the ultrasonic transducer was newly developed, and the ultrasonically-assisted hydrothermal method was examined by using this container. The effect of ultrasonic assist on the synthesis of lead-zirconate-titanate (PZT) thin films and (K,Na)NbO$_{3}$ powders was verified. Thicker PZT film, thickness around 10 ${\mu}$m, could be obtained in one process, and (K,Na)NbO$_{3}$ powder was synthesized in half the previous reaction time.}}, author = {{Ageba, Ryo and Kadota, Yoichi and Maeda, Takafumi and Takiguchi, Norihito and Morita, Takeshi and Ishikawa, Mutsuo and Bornmann, Peter and Hemsel, Tobias}}, issn = {{1948-5719}}, journal = {{Journal of Korean Physical Society}}, keywords = {{Hydrothermal method, High-power ultrasonic, PZT thin film, Lead-free piezoelectric materials}}, number = {{4}}, pages = {{918--923}}, title = {{{Ultrasonically-assisted Hydrothermal Method for Ferroelectric Material Synthesis}}}, doi = {{10.3938/jkps.57.918}}, volume = {{57}}, year = {{2010}}, } @article{9744, abstract = {{Direct ultrasound irradiation is advantageous to increase the efficiency of the hydrothermal method which can be used for the production of piezoelectric thin films and lead free piezoelectric ceramics. To apply ultrasound directly to the process transducer prototypes were developed regarding the boundary conditions of the hydrothermal method. LiNbO$_{3}$ and PIC 181 were proven as feasible materials for high temperature resistant transducers ($\geq 200^\circ C$). Resistance of the transducers horn against the corrosive mineralizer was achieved by using Hastelloy C-22. The efficiency of the ultrasound assisted hydrothermal method depends on the generated sound field. Impedance and sound field measurements have shown that the sound field depends on the filling level and the position and design of the transducer.}}, author = {{Bornmann, Peter and Hemsel, Tobias and Littmann, Walter and Ageba, Ryo and Kadota, Yoishi and Morita, Takeshi}}, issn = {{1948-5719}}, journal = {{Journal of Korean Physical Society}}, keywords = {{High-temperature transducer, Hydrothermal method, Lithium-niobate transducer}}, number = {{4}}, pages = {{1122}}, title = {{{Ultrasonic Transducer for the Hydrothermal Method}}}, doi = {{10.3938/jkps.57.1122}}, volume = {{57}}, year = {{2010}}, } @article{9758, abstract = {{As a lead-free piezoelectric ceramics, (K,Na)NbO$_{3}$ is a promising material because of its good piezoelectric properties. In this study, (K$_{1-x}$Na$_{x}$)NbO$_{3}$ ceramics were synthesized from a KNbO$_{3}$ and NaNbO$_{3}$ mixture powder prepared by the hydrothermal reaction. The hydrothermal reaction enables the production of high quality powder for the ceramics fabrication process. To obtain (K$_{1-x}$Na$_{x}$)NbO$_{3}$ ceramics, these two powders KNbO$_{3}$ and NaNbO$_{3}$ were mixed and then sintered together. X-Ray diffraction analysis revealed that the solid solution ceramics (K$_{1-x}$Na$_{x}$)NbO$_{3}$ was produced by the sintering process. The K/Na ratio in (K$_{1-x}$Na$_{x}$)NbO$_{3}$ ceramics was optimized for the best piezoelectric properties. The optimized forms was (K$_{0.48}$Na$_{0.52}$)NbO$_{3}$, which showed the following piezoelectric properties; k$_{33}$=0.56, d$_{33}$=114pC/N. In addition, the ferroelectric properties, P$_{r}$=7.72mC/cm$^{2}$, E$_{c}$=857V/mm, and the Curie temperature T$_{c}$=420$_{o}$C were also measured.}}, author = {{Maeda, Takafumi and Takiguchi, Norihito and Morita, Takeshi and Ishikawa, Mutsuo and Hemsel, Tobias}}, issn = {{1948-5719}}, journal = {{Journal of Korean Physical Society}}, keywords = {{Lead-free piezoelectric material, KNN, Hydrothermal method}}, number = {{4}}, pages = {{924--928}}, title = {{{Hydrothermal (K1-xNax)NbO3 Lead-free Piezoelectric Ceramics}}}, doi = {{10.3938/jkps.57.924}}, volume = {{57}}, year = {{2010}}, }