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Microwave Dielectric Ceramics with Rare-earth Elements (I)
히토시오사토,Isao Kagomiya,채기웅 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.6
Nearly half of the microwave dielectric materials include rare-earth elements based on a database presented by M. T. Sebastian. The presence of rare-earth elements helps to improve the microwave dielectric properties because the crystal structure is adjusted by the ionic radius of the rare-earth element. The microwave dielectrics are grouped by the crystal structure: (1) pseudotungstenbronze Ba<sub>6−3x</sub>R<sub>8+2x</sub>Ti<sub>18</sub>O<sub>54</sub> solid solutions, (2) homologous Ba<sub>n</sub>La<sub>4</sub>-Ti<sub>3+n</sub>O<sub>12+3n</sub> compounds (3) Y<sub>2</sub>BaCu<sub>2</sub>O<sub>5</sub> green phases, (4) aeschynite LaYTiO<sub>6</sub> and scheelite BaWO<sub>4</sub> compounds, (5) perovskite-type ABO<sub>3</sub> compounds, (6) garnet A<sub>3</sub>B'<sub>2</sub>B"<sub>3</sub>O<sub>12</sub> compounds. The materials group (3) - (6) are presented. We discuss the groups (1) - (2) in this paper, and presented in "Microwave Dielectric Ceramics with Rare-earth (II)".
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.
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.
Review and Prospect of Ferroelectricity and Magnetism in YMn2O5
Y. Noda,H. Kimura,I. Kagomiya,K. Kohn,N. Ikeda,S. Matumoto,T. Shobu,Y. Fukuda 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
YMn2O5 undergoes ferroelectric successive phase transitions at 39 K and 19 K, in which a dielectric constant shows anomalies. Spontaneous polarization was also observed. Just above these ferroelectric phase transition temperatures, at 45 K, antiferromagnetic order occurs. Neutron elastic measurements and magnetic susceptibility measurements reveal that the ferroelectric phase transition at 39 K and 19 K occurs simultaneously with the change of magnetic ordering pattern. Review of experimental results and conjecture for the origin of spontaneous polarization are given.??
Satoru Kobayashi,Hiroyuki Kimura,Isao Kagomiya,Kay Kohn,Toshihiro Osawa,Yukio Noda 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
A ferroelectric phase transition of RMn2O5 (R = rare earth,Bi,Y) has been systematically reinvestigated by dielectric measurements. In addition to a sharp peak of the dielectric constant along the b axis at the temperature of ferroelectric phase transition, TC1, we observed a small kink at TS slightly below TC1 for R = Er, Y, Tb, Tm. Correspondingly, two-step successive magnetic phase transitions were found for R = Er, Y, Tm in a narrow temperature range of 1 K around TC1 by neutron diraction measurements. The comparison between temperatures of dielectric anomalies and magnetic phase transitions indicates that the paraelectric-ferroelectric phase transition at TC1 is induced by a commensurate magnetic ordering along the c axis in RMn2O5.
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.
Frustrated minority spins in GeNi<sub>2</sub>O<sub>4</sub>
Matsuda, M.,Chung, J.-H.,Park, S.,Sato, T. J.,Matsuno, K.,Aruga Katori, H.,Takagi, H.,Kakurai, K.,Kamazawa, K.,Tsunoda, Y.,Kagomiya, I.,Henley, C. L.,Lee, S.-H. Editions de Physique 2008 Europhysics letters Vol.82 No.3
<P>Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNi<SUB>2</SUB>O<SUB>4</SUB> at <I>T</I><SUB><I>N</I>1</SUB>=12.1 K and <I>T</I><SUB><I>N</I>2</SUB>=11.4 K, respectively (Crawford M. K. <I>et al</I>., <I>Phys. Rev. B</I>, <B>68</B> (2003) 220408(R)). Using unpolarized and polarized elastic neutron scattering we show that the two transitions are due to the existence of frustrated minority spins in this compound. Upon cooling, at <I>T</I><SUB><I>N</I>1</SUB> the spins on the 〈111〉 kagome planes order ferromagnetically in the plane and antiferromagnetically between the planes (phase I), leaving the spins on the 〈111〉 triangular planes that separate the kagome planes frustrated and disordered. At the lower <I>T</I><SUB><I>N</I>2</SUB>, the triangular spins also order in the 〈111〉 plane (phase II). We also present a scenario involving exchange interactions that qualitatively explains the origin of the two purely magnetic phase transitions.</P>