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KenichiKakimoto,Lien Thi-Kim Nguyen,Yusuke Hayakawa,Yuya Shinkai,Isao Kagomiya 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
Preparation of alkali niobate ceramic powder of KNbO_3, (Na,K)NbO_3, and (Li,Na,K)NbO_3 has been carried out by using a citrate-based liquid precursor route which was a newly developed innovative wet powder processing technique. The derived powder showed a well-sinterable property and the sintered ceramics demonstrated excellent ferroelectric property. Orthorhombic KNbO_3 showed a remanent polarization (P_r) of 23.3 μC/cm^2 and coercive field (E_c) of 7.8 kV/cm, and (Na,K)NbO_3 showed a P_r of 31.4 μC/cm^2 and E_c of 17.3 kV/cm. On the other hand, tetragonal (Li,Na,K)NbO_3 demonstrated Pr of 19.0 μC/cm^2 and Ec of 13.6 kV/cm. The citrate liquid precursor route demonstrated a good potential for the synthesis of fine powders for lead-free alkaline niobate ceramics.
Thermal Discharge Phenomenon in Alkali Niobate Piezoceramics
Hitoshi Matsudo,KenichiKakimoto,Isao Kagomiya 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
The thermal discharge behavior of poled Na_(0.5)K_(0.5)NbO_3 (NKN) ceramics was studied by using thermally stimulated depolarization current (TSDC) measurements. When the heating rate was 1 ℃/min, the TSDC pattern contained an anomalous TSDC pattern below its Curie temperature at approximately 375 ℃. The activation energy of its thermal relaxation was calculated to be 0.54 eV by comparing with TSDC measurement with the heating rate of 2 ℃/min. The a.c. impedance measurement revealed that the ceramics contained an oxygen vacancy-related dielectric relaxation with a 0.56 eV activation energy. The generation of the anomalous discharge of the poled NKN ceramics originated from its thermal relaxation, and the relaxation was caused by the dipolar relaxation of oxygen ions rather than the ionic conduction of oxygen.
Influence of a 60˚ Domain Structure on the Orthorhombic Niobate-based Piezoelectric Property
Kohei Tsuchida,KenichiKakimoto,Isao Kagomiya 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.7
The present work investigated the dependence of domain switching (90˚ and 60˚ domains) on the piezoelectric property due to an applied electric field in Mn-doped Na<sub>0.55</sub>K<sub>0.45</sub>NbO<sub>3</sub> (Mn-NKN) ceramic samples. In addition, the electric-field-induced strain and temperature-dependent planar extensional electromechanical coupling factor kp were studied. The results indicate that the piezoelectric properties for the orthorhombic phase due to 60˚ domain switching are stable over a wide range of temperatures.