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

过渡金属化合物表现出金属导电性，通常处于混价状态。在铜硫化物系统中，尽管含有稀土元素Pr的化合物的组成实现了混合价状态，但它们变成了半导体。为了解释这一原因，我们利用库仑滴定方法测量了阳离子的价态，用Rietvert分析X射线衍射数据进行了价键估算，进行了铜的反铁磁共振(AFNMR)和核四极共振(NQR)。结果发现，Pr4f与铜的3d和/或氧2p轨道发生了杂化(混合)，通过一种费米表面效应(近藤效应)导致了掺杂到系统中的空穴的局域化。作为我们研究的结果，基于稀土元素Yb和3d过渡金属铜的组合，中间金属…更多具有立方Becu_5型结构的LiLi化合物体系YbCu5-x&Gt；Agx在整个组成x范围内表现出密集的近藤效应，其特征温度(近藤温度)是系统变化的。另一方面，等结构体系YbCu5-x&gt；In_x表现出从致密的Kondo体系(x=0)向伴随价态转变的涨落体系(x=1)的交叉。此外，在中间组合物中还观察到了近藤绝缘体的行为。在具有焦绿石型结构的强关联电子体系R_2V_2O_7和R_2Ru_2O_7(R为稀土元素)中也观察到了典型的受挫现象。在仪器的改进方面，我们对核磁共振仪器进行了改进，引入了宽带功率放大器和数字存储系统，以便能够测量去年的弛豫时间。在这一年里，我们引进了高分辨率的8T超导磁体来测量高分辨率的NMR。利用这个装置，我们在Ruthenate体系中进行了^&lt；17&gt；O核磁共振，并通过测量^&lt；17&gt；O核自旋-晶格驰豫时间来研究Ru自旋的动力学行为。结果发现，因瓦型化合物SrRuO_3并不遵循平均场局域矩模型和自旋涨落理论，这意味着该体系处于中间金属电子态。此外，虽然CaRuO_3被认为具有很强的反铁磁关联，但它的动力学行为表明该化合物是一个非常接近铁磁态的Pauli顺磁体，具有很强的铁磁自旋关联。我们对CaRuO_3的比热测量结果可以用巡回电子自旋涨落理论来解释，这与核磁共振的结果是一致的。此外，我们计划从微观和动力学的角度来研究Yb硫系化合物。较少

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