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Journal Articles

Nanoscale structural analysis of Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ in high-temperature phases

Yoneda, Yasuhiro; Noguchi, Yuji*

Japanese Journal of Applied Physics, 60(SF), p.SFFA08_1 - SFFA08_10, 2021/11

 Times Cited Count:0 Percentile:0(Physics, Applied)

Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (abbreviated as BNT) is a lead-free material but exhibits relatively large piezoelectric properties, a lot of researches have been conducted. We performed local structural analysis using high-quality BNT with a stoichiometrically correct composition, and found a chemical order structure of Bi/Na in locally. BNT undergoes a phase transition to a cubic phase at 400$$^{circ}$$C. We estimated that a new disorder structure will appear in the high-temperature phase. In the high temperature phase, pair distribution function (PDF) analysis using synchrotron radiation high-energy X-rays was performed. As a result, we found that Bi shifts from 200$$^{circ}$$C, and this shift becomes an order parameter for the phase transition.

Journal Articles

Local structure analysis of PbTiO$$_3$$ in high-temperature cubic phase

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Kitanaka, Yuki*; Noguchi, Yuji*

Ferroelectrics, 538(1), p.57 - 62, 2019/05

 Times Cited Count:3 Percentile:33.49(Materials Science, Multidisciplinary)

High-energy X-ray diffraction study was performed on lead titanate (PbTiO$$_3$$). Short-range order structure was revealed using atomic pair-distribution function (PDF) method. In the high-temperature cubic phase, there is a large deviation between local and average structure. Especially, Pb atoms deviated from the cubic lattice framework, but establish Pb-O-Pb random network.

Journal Articles

Local structure and phase transitions of KNbO$$_3$$

Yoneda, Yasuhiro; Ohara, Koji*; Nagata, Hajime*

Japanese Journal of Applied Physics, 57(11S), p.11UB07_1 - 11UB07_6, 2018/11

 Times Cited Count:9 Percentile:56.55(Physics, Applied)

Local structure analysis of KNbO$$_3$$, which is the parent compound for lead-free piezoelectric materials, have been performed by X-ray pair-distribution functions (PDF). The refinements of local structure in wide temperature ranges indicates that only the rhombohedral structure can describe the observed bond distributions within the unit cell. The rhombohedral distortion maintained locally in all four phases.

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:37.51(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$$_3$$.

Oral presentation

Atomic pair-distribution function (PDF) analysis by using bending magnet beamlines

Yoneda, Yasuhiro

no journal, , 

A $$kappa$$-type diffractometer, which is dedicated to Japan Atomic Energy Agency, is equipped on a bending magnet beamline at SPring-8. We performed atomic pair-distribution function (PDF) analysis on crystalline materials. For example, local and middle-ranges order analysis of surrogate materials of Dy$$_{1-x}$$Zr$$_x$$N for nitride fuel was performed by using this apparatus.

Oral presentation

Short- and middle-ranges order structure analysis of ferroelectric materials

Yoneda, Yasuhiro

no journal, , 

An invitation lecture about atomic pair distribution function (PDF) method which is one of the local structural analysis method using synchrotron radiation X-rays was performed. Since the PDF analysis can be clarified the nano-scale order structure, as well as the short-range order structure, the PDF analysis is structural analysis method indispensable to ferroelectric materials with a manifested organization of physical properties through the domain. I showed that the results of the PDF analysis for relaxor ferroelectrics. The PDF is able to visualize the structure of the lead atoms, which deviates from the average structure.

Oral presentation

Local structure analysis of PbTiO$$_3$$ in high-temperature cubic phase

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Kitanaka, Yuki*; Noguchi, Yuji*

no journal, , 

Lead titanate, PbTiO$$_3$$, has a tetragonal structure having a large c/a ratio at room temperature. A phase transition to the paraelectric phase at 490$$^{circ}$$C, structural changes to cubic. However, just above the transition point to the paraelectric phase, the phonon modes of the still ferroelectric is observed. Therefore, spontaneous polarization using a sample of reversible high quality, perform high-energy X-ray diffraction experiments were subjected to structural analysis in a wide temperature range from room temperature to 800$$^{circ}$$C. Short range order structure analysis and atomic two pairs distribution function (atomic pair-distribution function, PDF) was performed using. A comparison local structures at room temperature of the observed local structure and relaxor Pb (Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$ (PMN) with 800$$^{circ}$$C of PbTiO$$_3$$, network structure similar to the relaxor PMN is present in the high temperature phase of PbTiO$$_3$$ It is considered to have.

Oral presentation

Local structure analysis of Ca$$_x$$Ba$$_{1-x}$$Nb$$_2$$O$$_6$$ in high-temperature phase

Yoneda, Yasuhiro; Fu, D.*

no journal, , 

Ca$$_{1-x}$$Ba$$_x$$Nb$$_2$$O$$_6$$ (CBN) in which Ba of BaNb$$_2$$O$$_6$$ is replaced with Ca, which is a ferroelectric substance having a tungsten bronze structure, A single-phase tetragonal phase appears in the composition range where the amount of Ca substitution is 0.19 $$le$$ ${it x}$ $$le$$ 0.32. For CBN, superlattice reflection appears in the powder X-ray diffraction pattern even in ceramic samples. There is a long-period structure that is deviated from the average structure. Since superlattice reflection is still observed in the high-temperature phase, structural analysis was performed in the high-temperature phase. It was found that the average structure of the high-temperature phase well reflected the local structure of the room temperature phase. It is considered to be a phenomenon that reflects the reentrant phase transition peculiar to tungsten bronze.

Oral presentation

Pair distribution function analysis of simulated nuclear waste glass

Yoneda, Yasuhiro; Tsuji, Takuya; Matsumura, Daiju; Okamoto, Yoshihiro; Nagai, Takayuki

no journal, , 

In order to establish vitrification technology, it is important to clarify how various substances dispersed in glass exist. We made simulated glass by mixing various substances containing metallic element of the platinum group with raw material glass containing SiO$$_2$$-B$$_2$$O$$_3$$ glass as the main component. This simulated glass was heated to 600$$^{circ}$$C just above the melting point and observed by an X-ray diffraction experiment. The obtained X-ray diffraction profile revealed the local structure using the pair distribution function (PDF). Since the network structure of SiO$$_2$$ is strong, it is considered that the precipitated fine particles become wedges and the Si-O bond length is modulated.

Oral presentation

Local structure modeling for BaTiO$$_3$$

Yoneda, Yasuhiro; Nakata, Kengo*; Ohara, Koji*

no journal, , 

We analyze real-space fit and inverse Monte Carlo method (RMC) using the same material data and compare the results obtained to characterize each analysis method. We will report the result of barium titanate (BaTiO$$_3$$). BaTiO$$_3$$ is one of the substances whose real space fit is very difficult because Ba with high ionicity and Ti with high covalent bond are mixed. We discussed how to extract comparable data from the structural parameters obtained by each analysis method.

Oral presentation

Local structure analysis of relaxor ferroelectrics Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Noguchi, Yuji*

no journal, , 

Many structural models have been proposed for relaxer ferroelectrics Pb(Mg$$_{1/3}$$Nb$$_{2/3})$$O$$_3$$. We have shown that the Pb-O distance obtained from the mean structure differs from the Pb-O distance obtained from the X-ray absorption fine structure (XAFS). Since the deviation between the average structure and the local structure is considered to be derived from the characteristic environment of the Pb atom, the behavior similar to that of the Pb atom in the pyrochlore type Pb$$_2$$ Sn$$_2$$O$$_6$$ is assumed and the local structure is assumed. I tried structural modeling. A pair-distribution function (PDF) analysis was performed, and as a result of local structure modeling, it was suggested that there is a network structure of Pb atoms that is different from the periodicity of the lattice system.

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