Mixed-Valent State and Conductivity of Rare Earth-Transition Metal Chalcogenide

稀土-过渡金属硫属化物的混合价态和电导率

• 批准号: 07454186
• 负责人: YOSHIMURA Kazuyoshi
• 金额: $ 4.42万
• 依托单位: KYOTO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 1995
• 资助国家: 日本
• 起止时间: 1995 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07454186/
• 关键词: rare-earth chalcogenide; mixed- valent state; dense Kondo effect; strongly correlated electron; nuclear magnetic resonance; transition metal compound; itinerant-electron magnetism; 混合原子価; フェルミ液体; 核磁気共鳴; 金属化合物

Transition metal compounds, which show metallic conductivity, are generally known to be in mixed-valent states. Among copper chalcogenide system, the compounds containing the rare earth element Pr becomes semiconducting, although they have a composition in which the mixed-valent states are realized. In order to elucidate this reason, we have measured the values of valences of cations utilizing the Coulometric titration method, performed valence bond estimations from rietvert analyzes of X-ray diffraction data, done the copper antiferromagnetic nuclear resonance (AFNMR) and nuclear quadrupole resonance (NQR). As their results, it has been found that there occurs a hybridization (mixing) between Pr 4f and copper 3d and/or oxygen 2p orbitals, resulting in the localization of holes doped to the system through a kind of Fermi surface effect (Kondo effect).As a result of our investigation of compounds based on the combination of rare earth element Yb and 3d transition metal Cu, the intermeta … More llic compound system YbCu_<5-x>Ag_x with the cubic BeCu_5-type structure has been found to show a dense Kondo effect in the whole composition x-range, where the characteristic temperature (Kondo temperature) varies systematically. On the other hand, isostructural system YbCu_<5-x>In_x has been found to show a crossover from a dense Kondo system (x=0) to a fluctuating system accompanied with the valence transition (x=1). Furthermore, the Kondo insulator-like behavior was observed in the intermediate composition. Typical phenomena due to the frustration effect have also been observed in the strongly correlated electron system, R_2V_2O_7 and R_2Ru_2O_7 (R being rare earth element) compounds with the pyrochlore-type structure.As for improving the apparatus, we made a improvement of NMR apparatus by introducing the wide-band power amplifier and the digital memory system in order to be able to measure the relaxation time in the last year. In this year, we have introduced the 8T superconducting magnet with high resolution in order to measure high resolution NMR.By using this apparatus, we have performed the ^<17>O NMR in the ruthenate system and investigated the dynamical behavior of Ru spins by measuring ^<17>O nuclear spin-lattice relaxation time. As a result, it has been found that the invar-type compound SrRuO_3 does not follow the mean-field localized moment model as well as the spin fluctuation theory which is valid in the case of weak itinerant electron magnets, implying that the system is in the intermediate metallic electron state. Furthermore, although CaRuO_3 was thought to have strong antiferromagnetic correlation, its dynamical behavior indicates that this compound is a Pauli paramagnet being very close to the ferromagnetic state with a strong ferromagnetic spin correlation. Our result of the specific heat measurement on CaRuO_3 can be explained by the itinerant electron spin fluctuation theory, which is consistent with the NMR result.Furthermore, from now on, we have a plan to investigate the Yb chalcogenide compounds from the microscopic and dynamical view points. Less

过渡金属化合物通常已知在混合价值状态。在铜硫酸盐系统中，含有稀土元素PR的化合物变为半导体，尽管它们具有实现混合价值状态的组成。为了阐明这一原因，我们已经测量了利用Coulometric滴定方法的阳离子价值，从X射线衍射数据的Rietvert分析进行了价键估计，完成了铜抗铁磁核共振（AFNMR）和核Quadrupole rupole rupole resconance（NQR）。作为它们的结果，已经发现，在Pr 4F和铜3D和/或氧气2P轨道之间发生杂交（混合），从而导致通过一种Fermi表面效应（近kondo效应）将孔掺入系统的孔定位（因为我们的稀有地球元素YB和3D型Metal yb yb yb和3D的结果） YBCU_ <5-X> AG_X具有Cubic Becu_5型结构的AG_X在整个组合X范围内显示出密集的近核作用，其中特征温度（Kondo温度）会系统地变化。另一方面，已经发现IBCU_ <5-x> in_x的同建系统显示出从密集的近托系统（x = 0）到伴随价值转换（x = 1）的波动系统的交叉。此外，在中间组成中观察到了近代绝缘子样行为。 Typical phenomena due to the frustration effect have also been observed in the strongly correlated electronic system, R_2V_2O_7 and R_2Ru_2O_7 (R being rare earth element) compounds with the pyrochlore-type structure.As for improving the apparatus, we made a improvement of NMR apparatus by introducing the wide-band power amplifier and the digital memory system in order to be able to measure the去年放松时间。在今年，我们引入了具有高分辨率的8T超导磁铁，以测量高分辨率NMR。通过使用该设备，我们在修饰酸盐系统中执行了 ^<17> o nmr，并通过测量Ru Spins的动态行为来测量核型核自旋效果松弛时间。结果，已经发现，不向型化合物SRRRUO_3不遵循平均场局部矩模型以及旋转波动理论，而在弱巡回电子磁体的情况下，这是有效的，这意味着该系统在中间的金属电子状态中。此外，尽管人们认为Caruo_3具有很强的抗铁磁相关性，但其动态行为表明该化合物是Pauli Paramagnet非常接近具有强铁磁旋转相关性的铁磁状态。我们对Caruo_3的特定热测量结果的结果可以通过巡回电子自旋波动理论来解释，该理论与NMR结果一致。Furthermore从现在开始，我们有一个计划研究了微观和动态观点的YB Chalcogenide化合物。较少的

项目成果

R.L.Corey: "^<63>Cu(2)Nuclear Quadrupole and Nuclear Magnetic Resonance Studies of YBa_2Cu_4O_8 in the Normal and Superconducing States" Phys.Rev.B. 53(9). 5907-5914 (1996)

R.L.Corey：“^<63>Cu(2)核四极杆和 YBa_2Cu_4O_8 在正常和超导状态下的核磁共振研究”Phys.Rev.B。

K. Yoshimura: "Supercondueting Properties of the La_<1+x>Ba_<2-x>Cu_3O_y System" Advances in Superconductivity VII(Springer-Verlag). 377-380 (1995)

K. Yoshimura：“La_<1x>Ba_<2-x>Cu_3O_y 系统的超导特性”Advances in Superconductivity VII（Springer-Verlag）。

M. Kato: "Coulometric Determination of Pr in the Ln-Ba-Cu-O System" Proceedings (ISS'95), Advances in Superconductivity. VIII. 359-362 (1996)

M. Kato：“Ln-Ba-Cu-O 系统中 Pr 的库仑测定”论文集 (ISS95)，超导进展。

吉村一良: "化学分野" ISTEC. 9 (1). 14-15 (1996)

吉村和义：“化学” ISTEC 9 (1)。

H. Aruga-Katori: "Field-induced Valence Transition in YbIn_<1-x>Ag_xCu_4" Journal of Magnetism and Magnetic Materials. 140-144. 1245-1246 (1995)

H. Aruga-Katori：“YbIn_<1-x>Ag_xCu_4 中的场诱导价态跃迁”《磁性与磁性材料杂志》。