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Journal Articles

Temporally decoherent and spatially coherent vibrations in metal halide perovskites

Zhang, D.*; Hu, X.*; Chen, T.*; Abernathy, D. L.*; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Kofu, Maiko; Foley, B. J.*; Yoon, M.*; Choi, J. J.*; et al.

Physical Review B, 102(22), p.224310_1 - 224310_10, 2020/12

 Times Cited Count:1 Percentile:24.67(Materials Science, Multidisciplinary)

Journal Articles

Distance-selected topochemical dehydro-diels-alder reaction of 1,4-Diphenylbutadiyne toward crystalline graphitic nanoribbons

Zhang, P.*; Tang, X.*; Wang, Y.*; Wang, X.*; Gao, D.*; Li, Y.*; Zheng, H.*; Wang, Y.*; Wang, X.*; Fu, R.*; et al.

Journal of the American Chemical Society, 142(41), p.17662 - 17669, 2020/10

 Times Cited Count:6 Percentile:75.63(Chemistry, Multidisciplinary)

Solid-state topochemical polymerization (SSTP) is a promising method to construct functional crystalline polymeric materials, but in contrast to various reactions that happen in solution, only very limited types of SSTP reactions are reported. Diels-Alder (DA) and dehydro-DA (DDA) reactions are textbook reactions for preparing six-membered rings in solution but are scarcely seen in solid-state synthesis. Here, using multiple cutting-edge techniques, we demonstrate that the solid 1,4-diphenylbutadiyne (DPB) undergoes a DDA reaction under 10-20 GPa with the phenyl as the dienophile. The crystal structure at the critical pressure shows that this reaction is "distance-selected". The distance of 3.2${AA}$ between the phenyl and the phenylethynyl facilitates the DDA reaction, while the distances for other DDA and 1,4-addition reactions are too large to allow the bonding. The obtained products are crystalline armchair graphitic nanoribbons, and hence our studies open a new route to construct the crystalline carbon materials with atomic-scale control.

Journal Articles

Nanoscale relaxation in "Water-in-Salt" and "Water-in-Bisalt" electrolytes

Gonzal$'e$z, M. A.*; Borodin, O.*; Kofu, Maiko; Shibata, Kaoru; Yamada, Takeshi*; Yamamuro, Osamu*; Xu, K.*; Price, D. L.*; Saboungi, M.-L.*

Journal of Physical Chemistry Letters (Internet), 11(17), p.7279 - 7284, 2020/09

 Times Cited Count:6 Percentile:81.96(Chemistry, Physical)

Journal Articles

Multiple magnetic bilayers and unconventional criticality without frustration in BaCuSi$$_2$$O$$_6$$

Allenspach, S.*; Biffin, A.*; Stuhr, U.*; Tucker, G. S.*; Kawamura, Seiko; Kofu, Maiko; Voneshen, D. J.*; Boehm, M.*; Normand, B.*; Laflorencie, N.*; et al.

Physical Review Letters, 124(17), p.177205_1 - 177205_7, 2020/05

 Times Cited Count:5 Percentile:77.76(Physics, Multidisciplinary)

Journal Articles

Ultralow thermal conductivity from transverse acoustic phonon suppression in distorted crystalline $$alpha$$-MgAgSb

Li, X.*; Liu, P.-F.*; Zhao, E.*; Zhang, Z.*; Guide, T.*; Le, M. D.*; Avdeev, M.*; Ikeda, Kazutaka*; Otomo, Toshiya*; Kofu, Maiko; et al.

Nature Communications (Internet), 11(1), p.942_1 - 942_9, 2020/02

 Times Cited Count:15 Percentile:93.25(Multidisciplinary Sciences)

In high-performance thermoelectric materials, there are two main low thermal conductivity mechanisms: the phonon anharmonic and phonon scattering resulting from the dynamic disorder, which have been successfully revealed by inelastic neutron scattering. Using neutron scattering and ab initio calculations, we report here a mechanism of static local structure distortion combined with phonon-anharmonic-induced ultralow lattice thermal conductivity in $$alpha$$-MgAgSb. Since the transverse acoustic phonons are almost fully scattered by the intrinsic distorted rocksalt sublattice in this compound, the heat is mainly transported by the longitudinal acoustic phonons. The ultralow thermal conductivity in $$alpha$$-MgAgSb is attributed to its atomic dynamics being altered by the structure distortion, which presents a possible microscopic route to enhance the performance of similar thermoelectric materials.

Journal Articles

Cross-shell excitations from the $$fp$$ shell; Lifetime measurements in $$^{61}$$Zn

Queiser, M.*; Vogt, A.*; Seidlitz, M.*; Reiter, P.*; Togashi, Tomoaki*; Shimizu, Noritaka*; Utsuno, Yutaka; Otsuka, Takaharu*; Homma, Michio*; Petkov, P.*; et al.

Physical Review C, 96(4), p.044313_1 - 044313_13, 2017/10

 Times Cited Count:3 Percentile:36.02(Physics, Nuclear)

no abstracts in English

Journal Articles

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

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Fu, D.*

Ferroelectrics, 513(1), p.1 - 6, 2017/09

 Times Cited Count:6 Percentile:41.1(Materials Science, Multidisciplinary)

An EXAFS study of lead magnesium niobate was performed at the Nb K edge and at the Pb L3 edge at 300 K. Two Nb-O bond lengths of 1.91 and 2.10${AA}$ are observed and there is no significant modification of the local environment of the Nb atoms compared with NaNbO$$_3$$ and AgNbO$$_3$$. The weak Pb L3 EXAFS signal indicated a strong static disorder, which can be extracted by PDF analysis.

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 Nb-related perovskite materials

Yoneda, Yasuhiro; Kohara, Shinji*; Nagata, Hajime*; Fu, D.*; Takenaka, Tadashi*

Transactions of the Materials Research Society of Japan, 39(4), p.455 - 458, 2014/12

NaNbO$$_3$$, KNbO$$_3$$, and AgNbO$$_3$$ have rhombohedral structure at low temperatures. The phase transition depends on ${it A}$-site ion with NbO$$_6$$ octahedron. NaNbO$$_3$$ and KNbO$$_3$$ have structural phase transition from rhombohedral to orthorhombic with increasing temperature. On the other hand, the phase transition of AgNbO$$_3$$ occurs from rhombohedral to monoclinic. Since the rhombohedral structure is a highly ordered average structure, it tends to be subject to the influence of local randomness. We performed local structure analysis by using atomic pair-distribution function (PDF). The Nb-O bond clearly appeared in the observed distribution for NaNbO$$_3$$, but degraded in that for AgNbO$$_3$$. The difference of local structures causes different successive phase transitions for the Nb-related perovskite materials.

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.

Journal Articles

Local structure analysis of NaNbO$$_3$$

Yoneda, Yasuhiro; Fu, D.*; Kohara, Shinji*

Journal of Physics; Conference Series, 502(1), p.012022_1 - 012022_4, 2014/04

 Times Cited Count:10 Percentile:97.97

NaNbO$$_3$$ has an antiferroelectric structure at room temperature and finds important technological applications. It exhibits an unusual complex sequence of temperature- and pressure-driven structural phase transitions. NaNbO$$_3$$ shows unambiguous evidence for the presence of the ferroelectric $$R3c$$ phase coexisting with an antiferroelectric phase ($$Pbcm$$) over a wide range of temperatures. We have carried out atomic pair-distribution function (PDF) analysis on NaNbO$$_3$$ to understand the phase transitions. High-energy X-ray PDF using powder samples were carried out at the SPring-8, which is provided to become rhombohedral structure if ${it A}$-site atoms did order and to become antiferroelectric phase if ${it A}$-site atoms did disorder.

Journal Articles

Ni-substitution effects on the spin dynamics and superconductivity in La$$_{1.85}$$Sr$$_{0.15}$$CuO$$_{4}$$

Matsuura, Masato*; Fujita, Masaki*; Hiraka, Haruhiro*; Kofu, Maiko*; Kimura, Hiroyuki*; Wakimoto, Shuichi; Perring, T. G.*; Frost, C. D.*; Yamada, Kazuyoshi*

Physical Review B, 86(13), p.134529_1 - 134529_8, 2012/10

 Times Cited Count:6 Percentile:31.07(Materials Science, Multidisciplinary)

Oral presentation

Pulse radiolysis and mass spectrometry study on the one electron oxidation of 3-nitrotyrosine and its derivatives

Lin, M.; Shi, W.*; Fu, H.*; Muroya, Yusa*; Katsumura, Yosuke; Xu, D.*; Chai, Z.*

no journal, , 

The reaction between reactive nitrogen species (RNSs) such as peroxynitrite and nitrogen oxide (NOx), and aromatic amino acids such as tyrosine and tryptophan results in a number of modifications, of which tyrosine nitration has gained much attention. 3-Nitrotyrosine (3-NT) was considered as an important biomarker of nitrative stress ${it in vivo}$. In this work, the reaction rate constants of 3-NT, N-acetyl-3-nitrotyrosine ethyl ester (NANTE) and 3-NT containing peptide Gly-nitroTyr-Gly reacting with azide radical (N$$_{3}$$$$^{.}$$) at pH 6.0 were measured. The UV-visible absorption spectra of the transients of N$$_{3}$$$$^{.}$$ reacting with the above compounds were also investigated. The results implied the possibility of protein aggregation through covalent dimerization of 3-NT residue ${it in vivo}$.

Oral presentation

Local structure of NaNbO$$_3$$

Yoneda, Yasuhiro; Kohara, Shinji*; Fu, D.*

no journal, , 

NaNbO$$_3$$ which is one of the niobium system perovskite contains sodium of the alkaline metal at ${it A}$-site. Although composition was a difficult ferroelectric because of the deliquescence of an alkali metal oxide, this problem is also being conquered and a good sample came to be compounded in recent years. Then, in order to reconfirm the phase transition of NaNbO$$_3$$, the structural analysis using the two-body correlated distribution function method (PDF) which is one of the local order analyses was conducted. Usually, in the structure phase transition of a ferroelectric, local order hardly changes near the transition point. However, change of clear local order is seen in NaNbO$$_3$$, and a phase transition mechanism is under consideration.

Oral presentation

Local structure analysis of NaNbO$$_3$$, 2

Yoneda, Yasuhiro; Kohara, Shinji*; Fu, D.*

no journal, , 

In the last meeting, we reported the result of the local structure analysis for NaNbO$$_3$$ using the atomic pair-distribution function method (PDF). Although NaNbO$$_3$$ is believed that rhombohedral structure and orthorhombic structure exit together in the wide temperature range below room temperature. Since local structure was reproduced by calculation, assuming rhombohedral structure in all the temperature ranges, it is considered that ground state of NaNbO$$_3$$ is rhombohedral structure. It is known that the diffuse phase transition accompanied by these 2 phase coexistence replaces to a sharp phase transition when Na of A-site is substituted by Li. In this time, the local structure analysis of (Na$$_{0.9}$$Li$$_{0.1}$$) NbO$$_3$$ was performed in the previous manner. In the 2-phase coexistence phase, it was found that Bragg reflections became sharp by doping Li and rhombohedral structure was stabilized locally.

Oral presentation

Phase transition and local structure analysis of NaNbO$$_3$$

Yoneda, Yasuhiro; Kobune, Masafumi*; Wada, Satoshi*; Fu, D.*

no journal, , 

NaNbO$$_3$$ shows a complex phase transition sequence. The average structure transformed from an orthorhombic to rhombohedral structure at the phase transition temperature. This phase transition has been found to be diffuse and the orthorhombic and rhombohedral phases coexist at wide temperature ranges. The origin of the diffuse phase transition should be the randomness of the local structure. We performed atomic-pair distribution function analysis by using NaNbO$$_3$$ samples grown by various synthesis method to clarify the relationship between the local structure and the phase transition. We demonstrated that the off-center shift of Nb atoms from the center on NbO$$_6$$ ocrahedra coupled with the rhombohedral to orthorhombic phase transition.

Oral presentation

Oral presentation

High-energy X-ray diffraction study of Ca$$_x$$Ba$$_{1-x}$$Nb$$_2$$O$$_6$$

Yoneda, Yasuhiro; Fu, D.*

no journal, , 

It has been reported that a ferroelectric having a tungsten bronze structure has an electro-optic effect, a nonlinear effect, and a relaxor-like behavior. BaNb$$_2$$O$$_6$$, which has an orthorhombic structure at room temperature, shows a single-phase tetragonal structure in the composition range of 0.19$$le x le$$0.32 when Ca is added to the Ba site. I understand. In addition, disorder was generated in the ${it a-b}$ plane due to the substitution effect, and superlattice reflection was observed in the ${it c}$-axis direction despite the ceramic sample. Currently, a local structure model is being constructed based on these phenomena.

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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