Papers by Author: Kenichi Kakimoto

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Authors: Kensuke Wada, Kenichi Kakimoto, Hitoshi Ohsato
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Authors: Kiyotaka Tanaka, Kenichi Kakimoto, Hitoshi Ohsato
Abstract: The development of lead-free piezoelectric materials has been required from the viewpoint of environmental preservation. We focused the lead-free KNbO3-based systems, and used a chemical solution deposition (CSD) process to obtain their precursor. (Na1-xKx)NbO3 precursor solutions were prepared from metal alkoxides and solvents such as absolute ethanol and 2-methoxyethanol. Crystallization behavior of the precursor gels obtained from the above solutions was investigated by the thermogravimetry differential thermal analysis (TG-DTA) measurement.
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Authors: Seiji Koide, Kenichi Kakimoto
Abstract: Li,Na,K)NbO3 (LNKN) crystals were grown by an infrared convergence-type floating zone (FZ) method using SrTiO3 seed crystals to control the crystallographic orientation. The crystals were grown along the [10 direction of SrTiO3 seed crystal. It was a critical condition for the crystal growth that the descending speed of an upper shaft in the FZ furnace was faster than that of the lower shaft. The grown crystal sizes were about 10 mm in length and 5 mm in diameter. A relation between the Li content and Tc was investigated, and the result was compared with the case of polycrystalline ceramic samples.
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Authors: Hitoshi Matsudo, Kenichi Kakimoto, Isao Kagomiya
Abstract: Na0.5K0.5NbO3 (NKN) lead-free piezoceramics was synthesized by a solid state reaction method. The d.c. conductivitydc and a.c. impedance of the ceramics were measured at the temperature range from 550 oC to room temperature on cooling process. Thedc decreased linearly with decreasing temperature on Arrhenius plot, and the activation energy at the temperature range from 450 to 390 oC and from 390 to 160 oC were 0.65 and 0.90 eV, respectively. The slope change at 390 oC corresponded to Curie temperature of NKN ceramics so that the carriers of these thermally active conductions were alkali metal or oxygen ions in the NKN crystal structure. The impedance of NKN ceramics at high temperature showed two relaxation processes at high and low frequencies, and the leak current was mainly attributed by the conduction through the grain boundary with low impedance value on lower frequency relaxation.
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Authors: Tsutomu Tsunooka, Tomonori Sugiyama, Hitoshi Ohsato, Kenichi Kakimoto, Minato Andou, Yutaka Higashida, Hirotsugu Sugiura
199
Authors: Hitoshi Matsudo, Kenichi Kakimoto, Isao Kagomiya
Abstract: Lead-free Na0.5K0.5NbO3 (NKN) piezoelectric ceramics was synthesized by an ordinal solid state reaction method. The ceramics was electrically poled under 3 kV/mm at 150 oC for 30 min. The discharge current-flow was measured for the poled ceramics at the heating rate of 1 oC/min from room temperature up to 500 oC. The two sharp peaks were observed at 209 and 417 oC. These temperatures were corresponded to orthorhombic-tetragonal (TO-T) and tetragonal-cubic (TC) phase transition temperatures, respectively. The sharp peaks were mainly originated from the decrease of the spontaneous polarization. Additionally, the several large broad patterns were also observed at 280, 363 and 375 oC, According to the electromechanical coupling factor kp, which is the indicative parameter of the polarization, mainly decreased at TO-T and TC. These broad peaks were not associated with the spontaneous polarization. The peaks seem to have been originated from the discharge current of the oxygen ion migration on elevating temperature inside the poled NKN ceramics.
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Authors: Kenichi Kakimoto, Satoru Ishihara, Momoko Watanabe
Abstract: Lead-free Li0.06(Na,K)0.94NbO3 (LNKN) piezoelectric ceramics were sintered by a new process, “two-step mixing process”, in which a part of alkali source powders (RA) was initially preserved and mixed with the rest matrix powders after the calcinations step, in order to improve bulk density. Sintering of the LNKN ceramics was improved by this process, and the sample with RA = 5% had the highest bulk density of 4.34 g/cm3 (ca. 95%TD). The pore shape and the fracture morphology of the samples suggested the formation of a liquid phase. The present results indicated that the two-step mixing process was an universal approach for improvement in the densification of alkali niobate ststem.
108
Authors: Kiyotaka Tanaka, Kenichi Kakimoto, Hitoshi Ohsato
Abstract: Various KNbO3 powders have been derived from sol-gel process by using different preparation and heating conditions. KNbO3 powder derived from ethanol solution and fabricated at 800oC was most suitable as the raw material of KNbO3 bulk ceramics, because of the small grain size of about 250 nm and its homogeneous size distribution.
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Authors: Kenichi Kakimoto, Izumi Masuda, Hitoshi Ohsato
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Authors: Yumi Inagaki, Kenichi Kakimoto, Hitoshi Ohsato
Abstract: Mn-doped Na0.5K0.5NbO3 (NKN) crystals have been grown by self-flux method under several heat-treatment conditions. The cooling rate affected the quality of Mn-doped NKN crystals significantly. When the cooling rate was 0.5 oC/min at temperatures ranging from 1050 to 950 oC, the synthesized Mn-doped NKN crystal exhibited a single nucleation growth, compared with multinucleation growth when the cooling rate was 0.25 oC/min at temperatures ranging from 1050 to 950 oC. The frequency dependence on the ferroelectric P-E hysteresis loop of the Mn-doped NKN crystal was not observed at measurement frequency of 0.1 – 25 Hz. The annealed 0.5 mol% Mn-doped NKN crystal exhibited excellent P-E hysteresis loop with Pr of 45.0 μC/cm2 and Ec of 7.2 kV/cm.
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