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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:1 Percentile:75.87(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:5 Percentile:53.96(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:5 Percentile:62.41(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.

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