論文 - 長田　実

ラマン分光法による機能性セラミックスの評価 査読有り

長田実, 垣花眞人

機能材料   23 巻 ( 11 ) 頁： 38 - 48   2003年4月

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Raman scattering in YBa2Cu4O8 and PrBa2Cu4O8: Indications of pseudogap effects in nonsuperconducting PrBa2Cu4O8 査読有り

J Backstrom, M Rubhausen, M Kall, L Borjesson, AP Litvinchuk, M Kakihana, M Osada, B Dabrowski

PHYSICAL REVIEW B   61 巻 ( 10 ) 頁： 7049 - 7054   2000年3月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

By analysis of the Raman spectra of superconducting YBa2Cu4O8 (Y-124), we observe a suppression of low-energy electronic density of states that we link to changes in the Linewidth of the Ba-phonon mode. These effects occur at a temperature below 150 K, where also anomalies in resistivity and other physical properties take place. We argue that these changes in the Raman spectra of Y-124 are connected to the opening of a pseudogap. Analogous anomalies in resistivity and the Ba-phonon width in the nonsuperconducting homologue PrBa2Cu4O8 (Pr-124) below 150 K suggest that similar pseudogap effects can occur without a following transition to a superconducting state at st lower temperature.

DOI： 10.1103/PhysRevB.61.7049

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CuO-chain Raman scattering and photoinduced metastability in YBa2Cu3Ox 査読有り

M Kall, M Osada, M Kakihana, L Borjesson, T Frello, J Madsen, NH Andersen, R Liang, P Dosanjh, WN Hardy

PHYSICAL REVIEW B   57 巻 ( 22 ) 頁： 14072 - 14075   1998年6月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

Raman measurements in YBa2Cu3Ox (x=6.72-6.82) high-T-c superconductors reveal intense phonon scattering due to an electronic resonance localized near oxygen vacancies on the CuO chains. Below room temperature the resonance can be photobleached in a manner similar to reported persistent photoinduced superconductivity effects, indicating photon-assisted oxygen ordering or electron vacancy capture. By comparing Raman and x-ray diffraction data we establish a correlation between the stability of the photoinduced state and the oxygen-ordering kinetics in the CuO chains.

DOI： 10.1103/PhysRevB.57.R14072

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Raman-active phonons in Bi2Sr2-xLaxCuO6+d: Phonon assignment and charge-redistribution effects 査読有り

M Osada, M Kakihana, M Kall, L Borjesson, A Inoue, M Yashima

PHYSICAL REVIEW B   56 巻 ( 5 ) 頁： 2847 - 2851   1997年8月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

Phonon Raman spectra of Bi2Sr2-xLaxCuO6+d single crystals with x values close to 0, 0.4, and 0.8 have been investigated. Room-temperature measurements were performed in the five main polarization geometries, including the c-axis polarized configuration. We identify the 4A(1g) symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell, as well as several disorder activated phonon bands from the BiO and/or SrO layers. For an increasing degree of La doping, the O(2)(Sr) A(1g) mode at 624 cm(-1) softens by 12 cm(-1) between x = 0 and x = 0.8. We attribute this softening to a weakening of the Cu-O(2)(Sr)-Bi bond due to a reduction in Cu and Bi valences when going from the overdoped (x = 0) to the underdoped (x = 0.8) regime.

DOI： 10.1103/PhysRevB.56.2847

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Raman-active phonons in Bi2Sr2Ca1-xYxCu2O8+d (x=0-1): Effects of hole filling and internal pressure induced by Y doping for Ca, and implications for phonon assignments 査読有り

M Kakihana, M Osada, M Kall, L Borjesson, H Mazaki, H Yasuoka, M Yashima, M Yoshimura

PHYSICAL REVIEW B   53 巻 ( 17 ) 頁： 11796 - 11806   1996年5月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

The phonon Raman spectra of Bi2Sr2Ca1-xYxCu2O8+d (x=0-1) have been investigated in a number of well-defined single-crystal and polycrystalline samples. From the polarization and Y-doping dependence, and from a comparison with previous reports on Bi-based cuprates, we identify the (6A(1g)+1B(1g)) symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell. A large number of extra ''disorder-induced'' phonon bands are observed in the ab-plane polarized spectra. In contrast to most previous reports, we argue that the c-axis polarized phonon band around 629 cm(-1) is due to the O(2)(Sr)A(1g) vibration, while the exclusively ab-plane polarized band around 463 cm(-1) is induced by the O(3)(Bi)A(1g) vibration. With increasing Y doping we find that the vibrational modes involving atoms in the CuO2 planes rapidly increase in intensity as a result of the reduced metallic screening in the hole-depleted Y-doped samples. We also find that Y substitution gives rise to a substantial hardening of the O(1)(Cu)A(1g) and B-1g phonons by similar to 40 cm(-1), whereas the O(2)(Sr)A(1g) phonon is found to soften by similar to 20 cm(-1), when x increases from 0 to 1. The phonon frequency changes can be explained by the ''internal pressure'' induced by the decrease in the average Ca/Y ion size and an additional ''charge-transfer'' induced by the change in the Cu and Bi valences with Y doping.

DOI： 10.1103/PhysRevB.53.11796

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Phonon Raman scattering in Y1-xPrxBa2Cu4O8 (x=0-1) and (Y1-xPrx)(2)Ba4Cu7O15-delta (x=0-0.6) 査読有り

M Kall, AP Litvinchuk, P Berastegui, LG Johansson, L Borjesson, M Kakihana, M Osada

PHYSICAL REVIEW B   53 巻 ( 6 ) 頁： 3590 - 3597   1996年2月

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

We report on a Raman-scattering investigation of phonons in ceramic Y1-xPrxBa2Cu4O8 (Y(1-x)Pr(x)124) with x=0-1, and (Y1-xPrx)(2)Ba4Cu7O15-delta (Y(1-x)Pr(x)247) with x=0-0.6. It is found that the A(g) symmetry phonons of the BaO layers and the CuO double-chain layers increase in frequency with Pr content x, while B-2g and B-3g symmetry phonons decrease in frequency. In the Y(1-x)Pr(x)247 samples we are able to identify two symmetry allowed apical oxygen A(g) modes. The B-1g-like plane oxygen phonon softens by similar to 12% from x=0 to x=1, and exhibits a two-mode behavior at intermediate x in both Y(1-x)Pr(x)124 and Y(1-x)Pr(x)247. Polarized micro-Raman spectra of Pr124 crystallites show that several phonons are asymmetric, exhibiting Fano line shapes similar to what has been found in superconducting Y124. The variation in phonon frequencies with Pr content is similar to what has been reported for the single-chain cuprate Y1-xPrxBa2Cu3O7-delta (Y(1-x)Pr(x)123), and the changes can be understood from the variation in structural parameters. We do not observe any peculiarities that can explain the disappearance of superconductivity, or the different rates of T-c suppression in the three different Y-Ba-Cu-O systems, upon Pr substitution.

DOI： 10.1103/PhysRevB.53.3590

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