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Journal Articles

Local structure analysis of NaNbO$$_3$$ and AgNbO$$_{3}$$ modified by Li substitution

Yoneda, Yasuhiro; Aoyagi, Rintaro*; Fu, D.*

Japanese Journal of Applied Physics, 55(10S), p.10TC04_1 - 10TC04_5, 2016/10

 Times Cited Count:6 Percentile:37.08(Physics, Applied)

We analyzed the local structures of NaNbO$$_3$$ and Na$$_{0.94}$$Li$$_{0.06}$$NbO$$_3$$ by combining the X-ray absorption fine structure (XAFS) and atomic pair-distribution function (PDF) techniques. NaNbO$$_3$$ is known to be an antiferroelectric material at room temperature. It also undergoes a diffuse phase transition, in which an orthorhombic and a rhombohedral phases coexist over a wide temperature range. We identified a rhombohedral ground state structure of NaNbO$$_3$$ and assumed an order-disorder-type phase. We also found a disorder feature in the nearest-neighbor bond distance corresponding to the Nb-O bonds. The disordered bond distribution disappeared when Na was substituted for Li. A similar disorder feature was found in AgNbO$$_3$$.

Journal Articles

Local structure analysis of Li-substituted (Bi$$_{0.5}$$Na$$_{0.5}$$)TiO$$_3$$ and NaNbO$$_3$$

Yoneda, Yasuhiro; Aoyagi, Rintaro*; Fu, D.*; Takenaka, Tadashi*

Transactions of the Materials Research Society of Japan, 39(3), p.247 - 250, 2014/09

Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ and NaNbO$$_3$$ are ${it AB}$O$$_3$$ perovskite ferroelectric materials and they are considered to be promising lead-free ferroelectric materials because of their relatively high piezoelectric properties in lead-free piezoelectric ceramics. The purpose of this work was to clarify the local structures of Li-substituted Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ and NaNbO$$_3$$ to elucidate the mechanism of the stabilization of the ordered ferroelectric phase.

Oral presentation

Local structural change of CaCu$$_3$$Ti$$_4$$O$$_{12}$$ in low temperature phase

Yoneda, Yasuhiro; Yoshii, Kenji; Hayakawa, Hironori*; Aoyagi, Rintaro*; Ikeda, Naoshi*

no journal, , 

Insulating cubic compound CaCu$$_3$$Ti$$_4$$O$$_{12}$$ (CCTO) has attracted much interest because of its giant change in the dielectric response with temperature. This compound possesses a low-frequency dielectric constant, $$epsilon$$ $$sim$$ 10$$^4$$, which is only varying in the temperature range 100 - 600K. However, dielectric measurements indicated that the CCTO is electrically inhomogenious by analyzing its impedance. The inhomogenity may originated by grain and grain-boundary contributions. We performed synchrotron X-ray pair-distribution function (PDF) analysis in order to visualize this inhomogenity. The obtained PDF changed depending on the grain size. The PDF showed that the origin of huge dielectric constant is extrinsic Maxwell-Wagner type due to the sample inhomogenity.

Oral presentation

Local structure analysis of Li-substituted NaNbO$$_3$$

Yoneda, Yasuhiro; Ohashi, Takayuki*; Aoyagi, Rintaro*

no journal, , 

NaNbO$$_3$$ is a ${it AB}$O$$_3$$ perovskite ferroelectric materials and has antiferroelectric orthorhombic structure at room temperature. Li-substituted NaNbO$$_3$$ crystals show different phase transition sequence though have the same average structure. The purpose of this work was to clarify the local structures of Li-substituted NaNbO$$_3$$ and to elucidate the mechanism of the ferroelectric phase transitions. A local structure analysis was carried out using the X-ray pair-distribution function (PDF) obtained from high-energy synchrotron X-ray diffraction. A clear difference in the local structures of Li-substituted NaNbO$$_3$$ was found. The difference in the ferroelectric phase transition can be explained by the local environment around the ${it A}$-site atoms.

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