Lithium insertion into layered quaternary chalcogenides: CdIn2S2Se2

CdIn₂S₂Se₂, a new quaternary chalcogenide having a typical layered structure, has been characterized and its electrochemical behaviour in a room temperature lithium cell investigated. Thermogravimetric analyses and differential scanning calorimetry measurements, discharge experiments and micropolarization tests as well as X-ray investigations have been carried out and the results discussed. A quasi-plateau and an extended plateau are observed during the discharge of the (−) Li/1M LiClO₄PC/CdIn₂S₂Se₂ (+) cell to a 1.0 V cut-off, and up to 6 lithium equivalents per mole are inserted at 0.3 mA cm⁻². Lithium inserted in the region of the first plateau (around 1.35 V versus Li/L⁺) is not readily available and possibly produces a structural rearrangement of the cathode material, whereas fast kinetics and good reversibility occur in correspondence of the second plateau at about 1.20 V versus Li/Li⁺. A new amorphous phase has been observed after a deep discharge.     

Mn nuclear magnetic resonance studies in RMn2Ge2 (R = rare earths)

The ⁵⁵Mn NMR in RMn₂Ge₂ (R= La,Nd and Gd) were observed as a function of temperature. In Nd and Gd compounds the ⁵⁵Mn NMR frequencies exhibit anomalous temperature dependences owing the effects of rare earth sublattices. The ordering temperatures of the Nd and Gd sublattices are found to be 30 and 95 K, respectively.     

Nuclear orientation and NMRON in rare earths

The rare-earth or lanthanoid series of elements offers a rich ground for the study of both solid-state phenomena and nuclear physics. Some systematic investigations of these elements as host materials and as impurity isotopes have been performed using the nuclear orientation methods, and more can be expected in the near future owing to recent technical developments. A review of past work in this area is given, and the outlook for future experiments is summarized.     

稀土掺杂金红石相TiO2的第一性原理的定性计算

稀土掺杂金红石相TiO2的禁带宽度(带隙)是影响其吸收波长的主要因素,其决定TiO2的光催化活性.利用第一性原理密度泛函理论(Ab initio DFT)得出17种稀土掺杂金红石相TiO2的能态密度(DOS),结果表明:除Lu、Y、Yb和Sc四种稀土增大金红石相TiO2带隙外,其余13种稀土均很大程度地降低金红石相TiO2的带隙.因此,稀土掺杂金红石相TiO2具有广阔的研究前景.     

Electrical resistivity of dilute heavy rare earths in Lu

The scattering of conduction electrons by the localized moments of heavy rare earth ions in Lu is investigated by analysing previously published resistivity measurements. The crystal field splitting of the 4f-levels is taken into account and satisfactory agreement obtained with experiment.     

稀土（Tb，Gd）掺杂多孔硅的光致发光性能研究

用电化学方法对多孔硅薄膜进行了稀土（Tb，Gd）离子的化学掺杂.利用荧光分光光度计测试了样品的光致发光特性.用扫描电子显微镜研究了薄膜的表面形貌.用卢瑟福背散射谱分析了稀土离子在多孔硅薄膜中的分布情况.结果表明，Tb的掺入显著增强了多孔硅的发光强度，并且发光峰位出现蓝移.这是由于Tb³⁺的4f能级⁵D_{4—⁷F3，⁵D4—⁷F关键词： 多孔硅 稀土掺杂 光致发光}     

The puzzle of high temperature superconductivity in layered iron pnictides and chalcogenides

The response of the worldwide scientific community to the discovery in 2008 of superconductivity at T _c?=?26?K in the Fe-based compound LaFeAsO_1?x F _x has been very enthusiastic. In short order, other Fe-based superconductors with the same or related crystal structures were discovered with T _c up to 56?K. Many experiments were carried out and theories formulated to try to understand the basic properties of these new materials and the mechanism for T _c. In this selective critical review of the experimental literature, we distill some of this extensive body of work, and discuss relationships between different types of experiments on these materials with reference to theoretical concepts and models. The experimental normal-state properties are emphasized, and within these the electronic and magnetic properties because of the likelihood of an electronic/magnetic mechanism for superconductivity in these materials.     

A systematic neutron diffraction study of RBa2Cu3O7 (R=yttrium and rare earths) high-T c superconductors

The 10K crystal structures of high-T _c RBa₂Cu₃O₇ (R=Y and rare earths) ceramic materials investigated by neutron diffraction were consistently analysed concerning systematic trends. Several interionic distances exhibit the well known lanthanide contraction behaviour, i.e., a linear relationship with the ionic radii of trivalent rare-earth ions. The only exceptions are associated with the apex oxygen O(1) ions: the chain copper Cu(1)–O(1) distances are constant, and the plane copper Cu(2)–O(1) distances are increasing across the rare-earth series. For R=Pr the 4f–CuO₂ valence band hybridization effects are found to be highly anisotropic, since exclusively the interionic distances involving the b-direction (i.e, the chain direction) indicate that the Pr ions have an intermediate valence of about+3.4.     

Magnetic properties of ternary gallides of type RNi4Ga (R=rare earths)

The magnetic properties of RNi₄Ga (R=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu) compounds have been investigated. These compounds form in a hexagonal CaCu₅ type structure with a space group P6/mmm. Compounds with the magnetic rare earths, R= Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm, undergo a ferromagnetic transition at 5, 17, 20, 19, 12, 3.5, 8 and 6.5 K, respectively. The transition temperatures are smaller compared to their respective parent compounds RNi₅. PrNi₄Ga is paramagnetic down to 2 K. LaNi₄Ga and LuNi₄Ga are Pauli paramagnets. All the compounds show thermomagnetic irreversibility in the magnetically ordered state except GdNi₄Ga.     

Screening of 3d holes in the rare earths

The origin of high- and low-energy satellites in rare earth 3d X-ray ohoto- emission spectra are elucidated in terms of the electronic configurations of the final states and related to the screening of the core hole. The role of the two competing mechanisms, change in 4f occupation number and conduction electron screening, is investigated. The 4f levels play a dominant role in strongly insulating compounds. The implications on the study of valence fluctuation compounds are discussed.     

Nonradiative decay from 5d states of rare earths in crystals

Nonradiative decay from 4f^n?1 5d states was investigated for trivalent rare earths in Y₃Al₅O₁₂. The rates of both 5d→4f and 5d→5d transitions were determined from measurements of the lifetimes and intensities of 5d fluorescence from Ce³⁺ and Pr³⁺. Because of the stronger ion-lattice coupling, nonradiative decay rates for transitions involving 5d states are much faster than those between 4f states. Decay rates are dependent upon the temperature and the energy gap to the next-lower level. The temperature dependences of the 5d fluorescence lifetimes from 77 to 700°K are reported.     

Large single-crystal growth of RBa2Cu3O7−x by the flux method (R=Y and rare earths)

Il Nuovo Cimento D - In this work the thermal conditions required for single-crystal growth in RBa2Cu3O7−x systems (R=Y or rare earths apart from Ce and Tb) have been systematically revised...     

Magnetic correlations in a layered iridate, Na(2)IrO(3)

Analysis of published data gathered on a sample of Na(2)IrO(3), held deep inside the antiferromagnetic phase at 1.58?K, shows that iridium magnetic dipole moments, measured in resonant x-ray Bragg diffraction, lie in the a-c plane of the monoclinic crystal and enclose an angle ≈118°?with the c-axis. These findings, together with bulk measurements, are united in a plausible magnetic ground state for an iridium ion constructed from a Kramers doublet. A magnetic space group, derived from the chemical space group C2/m (unique axis b), possesses an anti-translation, to accommodate antiferromagnetic order, and an odd, two-fold axis of rotation symmetry on the b-axis, [Formula: see text], placing Ir magnetic dipoles perpendicular to the b-axis. Anapoles (toroidal dipoles) are predicted to be likewise confined to the a-c plane, and magnetic charges forbidden.     

Surface valence changes in rare earths monitored by giant-resonance electron energy losses

Electron energy loss spectroscopy of 4d giant resonances in the rare earths is shown to be a sensitive monitor of valence changes in surface reactions with O₂ and S. Yb is found to be divalent on exposure to S but forms a trivalent oxide, while Gd is consistently trivalent. Eu forms a monosulfide, and an oxide of possibly mixed divalent and trivalent stoichiometry, while for Sm mixture of divalent and trivalent spectral features is consistently observed.     

Study of the 4f-levels in rare earths by appearance potential spectroscopy

The yttrium M_4.5-level Auger electron appearance potential spectrum (AEAPS) in the 150–190 eV energy range is presented. AEAPS is a surface sensitive technique that measures the differential secondary electron yield as a function of incident electron energy. The spectral features of AEAPS are determined by the width of the empty conduction band and the degree of localization of the conduction band wave functions. Yttrium (Y) is considered to be one of the rare earth metals with an absence of a 4f state. In lanthanum (La), which has an identical valence electron configuration-to Y, the 4f levels are localized. Comparison of the 3d-level spectrum of Y with that of La shows that though the main peaks remain the same, additional fine structures appear in the spectrum of La. The existence of these structures is correlated with the presence of empty localized 4f levels in La.     

On the magnetic arrangement in the diamagnetically substituted rare earths iron garnets

The magnetic arrangement in the rare earth iron garnet with diamagnetic substitution in octahedral sites, at 0 K, is calculated on the basis of the model of localized canting, when the exchange interaction between rare earth and iron ions is taken into account. The magnetization measurements on scandium substituted gadolinium iron garnet and neodymium iron garnet are reinterpreted.     

Many body satellite in the photoemission spectra of the heavy rare earths

A narrow feature is reported in the photoemission spectra of the heavy rare earths, Gd, Tb, and Dy on a variety of substrates. This feature is not expected from the initial densities of states. This feature appears to require a density of states at the Fermi energy to exist. We propose that the feature is due to a many electron shakeup process to the unoccupied 4f levels.