Yb Compounds Research Articles

Characterisation of thin films of the organic infra-red emitters Yb- and Er-tris(8-hydroxyquinoline) by X-ray photoemission spectroscopy

Thin films of the rare earth tris(8-hydroxyquinolines) YbQ 3 and ErQ 3 were evaporated in ultra-high vacuum, and studied by X-ray photoelectron spectroscopy (XPS). Evaporation was monitored by mass spectroscopy of the major cracking products, which have masses >200 a.m.u. and show further splitting due to wide isotope distributions. C and N 1s XPS data are very similar to those of aluminium tris(8-hydroxyquinolines), implying very similar ligand behaviour, while the O 1s binding energy was significantly higher, indicating a more ionic metal–oxygen bond. YbQ 3 was found to be completely trivalent, with no indication of the mixed valence behaviour observed in other Yb compounds.

Yb2Ge, Eu2Ge and Eu2Si: New PbCl2‐Type Compounds.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Spectroscopic properties of Yb-doped scandium based compounds Yb:CaSc2O4, Yb:SrSc2O4 and Yb:Sc2SiO5

Abstract Three Yb3+-doped scandium based materials are elaborated and their optical properties investigated. Scandium materials exhibit large energy levels splitting and favorable thermal properties. The energy level diagrams for Yb:CaSc2O4, Yb:SrSc2O4, and Yb:Sc2SiO5 are determined through optical spectroscopic analysis and semi-empirical crystal-field calculations using the simple overlap model. Laser parameters for Yb:Sc2SiO5 are compared to Yb:Y2SiO5 ones. Yb:Sc2SiO5 looks promising since it melts congruently and exhibits larger overall splitting of the 2F7/2Yb3+ ground state and broader absorption line width.

Transport Properties of Heavy Fermion Compounds: YbIn1−xCu4+x and YbIn1−yAg y Cu4

The intermetallic compounds of Yb with In and Cu (YbIn1−xCu4+x) and Yb with In, Ag, and Cu (YbIn1−yAg y Cu4) exhibit interesting magnetic and transport properties. Of the compounds of Yb with In and Cu the compound with x=0, namely YbInCu4, has attracted particular attention, because—while being a Curie–Weiss paramagnet—it undergoes a first-order isostructural phase transition at T v =approx. 40 to 80 K and atmospheric pressure. Below T v the ytterbium in this compound is in a mixed-valence state and the compound as a whole is sometimes called a light heavy-fermion system. Above T v , the compound is known as a Curie–Weiss paramagnet of localized magnetic moments and, below T v , a Pauli paramagnet in a nonmagnetic Fermi-liquid state. In the present paper the results of measurements of the thermal conductivity of polycrystalline samples, YbIn1−xCu4+x with x=0,0.015, 0.095, and 0.17 and YbIn1−yAg y Cu4 with y=0, 0.3, 0.7, and 1.0, are reported. The thermal conductivity is separated into the phonon thermal conductivity (κ ph ) (i.e., related to the heat carried by phonons) and into the electronic thermal conductivity (κ e ) (related to the heat carried by electrons). The electrical resistivity of the compounds was measured to determine the temperature dependence of the Lorenz number. The results show that in the temperature interval 4.2 to 300 K the latter quantity behavior follows the theoretical predictions for heavy fermion materials.

Growth and Characterization of YbBCO Films on Textured Gd2O3 Buffer-Layered Ni Tapes: All Sol–Gel Process

YbBa2Cu3O7−x (YbBCO) thick films were grown on buffered, cube-textured Nickel tapes by sol–gel dip-coating method. Yb-123 films were prepared using solutions of Yb, Ba, and Cu organometallic compounds. A solution-based Gd2O3 buffer layer was deposited by dip-coating process with excellent texture and uniformity. The texture development and surface morphology of the buffer-layer films were examined by X-ray diffraction, pole figures, and ESEM analysis. Microstructure and characterization of Yb-123 films were done by ESEM, EDS, and XRD analysis. Tc and Jc were conducted by four-wire measurement method

Dynamics of intrinsic optical bistability in two weakly interacting quantum systems

The dynamics of the intrinsic optical bistability (IOB) in an elementary quantum system is investigated in the situation where this system is composed of two weakly interacting subsystems. Numerical calculations have been performed for two 'real' systems where IOB has been experimentally observed. The first situation corresponds to the electron-nuclear spin system of {beta}-Ga{sub 2}O{sub 3}, where the transition between electron spin states exhibit a strong bistability. The other situation corresponds to optical transitions in Yb{sup 3+} pairs in CsCdBr{sub 3}:Yb compound, where IOB has been experimentally observed. It is shown that, in addition to the classical hysteresis of the response of the system upon variation of the power of the external field, the observation of the so-called critical slowing down is a clear signature of IOB.

Yb 2Ge, Eu 2Ge and Eu 2Si: new PbCl 2-type compounds

The intermetallic compounds Yb 2Ge, Eu 2Ge and Eu 2Si were synthesized from the elements by HF melting in tantalum crucibles. The three phases crystallize in the PbCl 2 structure type, as shown by Rietveld refinement of powder pattern intensity data. The structure of Yb 2Ge was confirmed by a single crystal study.

SYNTHESIS AND CHARACTERIZATION OF METAL COMPLEXES OF P,P′-DI[3-(TRIMETHYLSILYL)-1-PROPYL] METHYLENEDIPHOSPHONIC ACID

ABSTRACT The silicon-substituted diphosphonic acid P,P′-di[3-(trimethyl-silyl)-1-propyl] methylenediphosphonic acid, H2DTMSP-[MDP], reacts with metal nitrates in methanol to form complexes M2(DTMSP[MDP])3 for M˭Fe, Eu and Yb and M(DTMSP[MDP])2 for M˭Th. The sodium salt, Na2-(DTMSP[MDP]), forms upon neutralization of H2DTMSP-[MDP] with NaOH. The calcium salt, Ca(DTMSP[MDP]), forms upon addition of the aqueous metal nitrate to an equivalent amount of the neutralized ligand in methanol. Elemental analysis, infrared spectroscopy and magnetic susceptibility measurements were used to characterize the compounds. Frequency shifts in the asymmetric and symmetric POO− stretching bands of the Fe, Eu, Yb and Th compounds indicate symmetrical coordination of the phosphonate groups through chelate and/or bridging interactions. The frequency difference between these stretching bands becomes smaller as the ionic potential (e/r) of the metal ion increases.

Synthesis, crystal structure, and magnetic properties of ordered perovskites Sr 2LnTaO 6 (Ln = lanthanides)

A series of Sr 2LnTaO 6 (Ln=lanthanides except for La, Ce, and Pr) has been prepared by a standard ceramic method and their crystal structure has been determined by powder X-ray diffraction using the Rietveld analysis method. The crystal symmetry of their oxides is monoclinic (space group P2 1/ n) with an ordered arrangement of Ln and Ta ions. Magnetic susceptibility measurements show that these compounds are paramagnetic down to 5 K. The 151 Eu Mössbauer spectrum for Sr 2EuTaO 6 indicates that the Eu ion is in the trivalent state. The symmetry of the Eu site is distorted from the octahedral symmetry, and its spin–orbit coupling constant is determined to be 342 cm −1. In the Yb compound, the energy levels in the octahedral crystal field splitting are determined to be E Γ 7− Γ 6 =1324 and E Γ 8− Γ 6 =391 cm −1 by calculating the magnetic susceptibility.

Pseudogap Formation in Rare-Earth Compounds

The generalized periodic Anderson model with plane-wave conduction-band states is considered as a model to describe the properties of Ce, Sm, Eu, Tm and Yb compounds showing a variety of valence fluctuation phenomena. The mixing matrix elements between localized 4 f -electron states and the conduction-electron states, which are anisotropic in k space, are derived, and it is shown how pseudogap or real-but-anisotropic gap is formed in this model. The structures of gap or pseudogap to be derived here are considered to bear some of the characteristics of those of rare-earth compounds in such as heavy-fermion, Kondo-insulator and intermediate-valence states.

Two Hydroxo Bridged Dinuclear Lanthanide Phen Complexes: [Ln2(phen)4(H2O)4(OH)2](phen)2(NO3)4 with Ln = Tm, Yb

Abstract Two isostructural hydroxo bridged dinuclear lanthanide phen complexes of general composition [Ln2(phen)4(H2O)4(OH)2](phen)2(NO3)4 with Ln = Tm (1), Yb (2) were prepared by reactions of the corresponding lanthanide nitrate and phenanthroline monohydrate in CH3OH/H2O at pH = 5.5. They crystallize in the triclinic space group P1̄ (no. 2) with the cell dimensions: a = 11.233(1), b = 11.456(1), c = 14.011(2) Å , α = 93.91(1)°, β = 98.20(1)°, γ = 108.21(1)°, V = 1683.0(3)Å3, Z = 1 for 1 and a = 11.236(1), b = 11.480(2), c = 13.986(2)Å , α = 93.91(1)°, β = 98.17(1)°, γ = 108.33(1)°, V = 1682.9(3) Å3, Z = 1 for 2. The crystal structures are composed of the hydroxo bridged dinuclear [Ln2(phen)4(H2O)4(OH)4]4+ complex cations, hydrogen bonded NO3 - anions and π-π stacking (phen)2 dimers. The lanthanide atoms are each surrounded by two phen ligands, two H2O molecules and two μ-OH groups to complete a tetragonal antiprismatic LnN4O4 coordination. Via two common μ-OH groups, two neighboring tetragonal antiprisms are condensed to form a centrosymmetric dinuclear [Ln2(phen)4(H2O)4(OH)4]4+ complex cation. The complex cations and (phen)2 dimers are assembled via π-π stacking interactions and hydrogen bondings into 2D layers parallel to (101̄), between which the hydrogen bonded NO3 - anions are sandwiched. The Tm compound shows paramagnetic behavior with an experimental magnetic moment of 7.51 μB at room temperature. No magnetic ordering is evident down to 5 K. Over the temperature range 70 - 300 K, the Yb compound obeys the Curie-Weiss law with an experimental magnetic moment of 4.32 μB at room temperature and shows weak ferrimagnetic behavior at low temperature.

Thermoelectric Properties of Binary Cd–Yb Quasicrystal and Its Approximant

The thermoelectric properties of the binary quasicrystal Cd84.6Yb15.4 and its approximant Cd6Yb are reported. The thermopowers decrease linearly from 14 and 12 µV/K, respectively, with decreasing temperature from 300 K. The resistivities at 300 K are 180 and 150 µΩ·cm, respectively, and decrease rapidly on cooling below 100 K. These results indicate that Cd–Yb compounds possess a metallic nature, in contrast to the semiconductor-like behavior of conventional ternary quasicrystals. The phonon thermal conductivity κph(T) of Cd–Yb compounds shows no maximum, but is described by a power law, κph∝Tn, with n=0.5 and 1.0, respectively, for Cd84.6Yb15.4 and Cd6Yb. The thermoelectric dimensionless figures of merit ZT are estimated to be 0.003 and 0.004 at 300 K, respectively.

Field and pressure response of Yb compounds close to a quantum critical point

YbCu5−xAlx provides the possibility to tune ground state properties by a change of the valence due to the Cu/Al substitution, by pressure as well as by the application of a magnetic field. Near to the critical concentration xcr≈1.5 non-Fermi-liquid properties (NFL) are obvious, obeying hyperscaling. If magnetic order sets in for x>1.5, the application of moderate magnetic fields quenches order and again NFL features become evident. Hyperscaling in this case indicates strongly interacting spin fluctuations.

Narrow photoemission peak at the Fermi level in Fe/Cu(111).

We have studied electronic states of Fe adatoms deposited on Cu(111) by photoemission spectroscopy and have found a narrow peak at the Fermi level in the Fe 3d spectral function. The Fe 3d spectral function would be consistent with the Anderson impurity model, which has been widely used for the interpretation of bulk Ce and Yb compounds. This result indicates a strong reduction of hybridization between the Fe 3d state and the conduction-band states and an enhancement of effective Coulomb interaction for the Fe 3d electrons in an Fe adatom on Cu(111).

Magnetic susceptibility and specific heat studies on heavy rare earth ruthenate pyrochlores R2Ru2O7 (R = Gd–Yb)

Magnetic susceptibility and specific heat measurements were performed for heavy rare earth ruthenate pyrochlores R2Ru2O7 (R = Gd, Tb, Dy, Ho, Er, Tm, and Yb). The compounds of R = Tb, Er, and Yb show magnetic transitions at 3.4, 5.4, and 6.3 K, respectively, in the magnetic susceptibility vs. temperature curves. λ-Type anomalies indicating long-range magnetic ordering are observed in the specific heat vs. temperature curves for all of the compounds. At very low temperatures, the presence of short-range magnetic interactions between the rare earth ions for R = Tb, Er, and Yb compounds is indicated from both the susceptibility and the specific heat data.

The thermoelectric power of Kondo cerium and ytterbium compounds

The temperature dependence of the thermoelectric power (TEP) of Kondo Ce and Yb compounds is theoretically studied by a new approach: for T⪢TK, we start from the Coqblin–Schrieffer Hamiltonian including the crystalline field effect and we use a renormalized perturbation expansion with the coupling constants calculated by the “poor man's scaling” method; for T⪡TK, we use an effective spin-12 periodic Anderson model. This treatment can give a negative peak at low temperatures and a positive one at high temperatures, in good agreement with the TEP curves of many Ce compounds.

Electronic Structures of the Kondo Semiconductor YbB12: Temperature and Non-Magnetic Dilution Effects

We present our optical studies on the Kondo semiconductor YbB 12 , and on the “diluted” compounds Yb 1- x Lu x B 12 (0 ≤ x ≤1). The optical conductivity spectrum σ(ω) of YbB 12 is characterized by the opening of an energ gap of ∼20 meV below 80 K, and a pronounced mid-infrared (IR) peak which is also strongly temperature ( T ) dependent. For Yb 1- x Lu x B 12 with increasing x , the clear gap for x =0 is rapidly filled in from the bottom, and the mid-IR peak shows large red shifts. It is shown that increasing T and increasing x have qualitatively very similar effects on the energy gap and the mid-IR peaks. We discuss the evolutions of Yb 4 f -related electronic states near the Fermi level with T and x , and its relation to the gap evolution.

Chalcogen rich lanthanide clusters from halide starting materials (II): selenido compounds.

Lanthanides reduce mixtures of I(2) and PhSeSePh in THF, and the resultant heteroligand mixture reacts further with elemental Se in pyridine to give (THF)(6)Ln(4)I(2)(SeSe)(4)(mu(4)-Se).THF (Ln = Tm, Ho, Er, Yb). These selenium rich clusters contain a square array of Ln(III) ions connected through a single (mu(4)-Se) ligand. There are two I(-) ligands coordinating nonadjacent Ln(III) ions on the side of the cluster opposite the (mu(4)-Se), and the edges of the square are bridged by mu(2)-SeSe groups. The electronic spectrum of the Yb compound contains two absorption maxima that can tentatively be assigned as Se(2-) to Yb and SeSe to Yb charge-transfer absorptions, by comparison with the featureless absorption spectra of the Tm, Ho, and Er derivatives. With a 1/1/1/1 Yb/I/Ph(2)S(2)/Se stoichiometry, chalcogen rich compounds are not obtained, but instead, in Yb chemistry, the selenido cluster (THF)(10)Yb(6)Se(6)I(6) can be isolated in 51% yield. The molecular structure of this compound contains a Yb(4)Se(4) cubane fragment, with an additional Yb(2)Se(2) layer capping one face of the cube. Each Yb coordinates a terminal I(-). This intensely colored compound also has an absorption maximum in the visible spectrum. Upon thermolysis, the selenium rich compounds give Ln(2)Se(3) that is free of iodide contamination.

Low-temperature properties of YbZn2Sb2

We report synthesis and properties of the ternary Yb compound YbZn2Sb2. The resistivity, magnetization and specific heat at low temperature and high magnetic field of YbZn2Sb2 are typical of a strongly diamagnetic semimetal. A comparison with isostructural YbZn2As2 suggests that YbZn2Sb2 will undergo a nonmagnetic to magnetic quantum phase transition at high pressure that is driven by a valence transition.

Ternary lanthanoid ruthenium gallides with a high gallium content: Ln(2)Ru(3)Ga(10) (Ln = Yb, Lu) with a new structure type and LnRu(2)Ga(8) (Ln = La-Nd) with CaCo(2)Al(8)-type structure.

The title compounds were prepared by reaction of the elemental components at high temperatures. The compounds Yb(2)Ru(3)Ga(10) and Lu(2)Ru(3)Ga(10) crystallize with a new structure type, which has been determined from the single-crystal X-ray data of Yb(2)Ru(3)Ga(10): P4/mbm, Z = 2, a = 881.9(1) pm, c = 632.5(1) pm. In this structure the gallium atoms form two-dimensionally infinite double layers that extend perpendicular to the tetragonal axis. They contain two-thirds of the ruthenium atoms. The other ruthenium and the ytterbium atoms are situated between the gallium double layers. The structure is closely related to that of Mn(2)Hg(5). The latter compound may be written with the formula Mn(2)Mn(2)(square)Hg(10), thus indicating that its structure may be regarded as a defect-variant of the presently reported structure of Yb(2)Ru(3)Ga(10). The four gallides of the series LnRu(2)Ga(8) (Ln = La-Nd) crystallize with the orthorhombic CaCo(2)Al(8)-type structure (Pbam, Z = 4). This structure has been refined from single-crystal X-ray data of the cerium and neodymium compounds. Slight deviations from the ideal composition for one of the two ruthenium sites resulted in the formulas CeRu(1.913(4))Ga(8) and NdRu(1.858(4))Ga(8). Magnetic susceptibility measurements with a SQUID magnetometer indicate diamagnetism for LaRu(2)Ga(8), which is partially compensated by the expected Pauli paramagnetism. The cerium atoms in CeRu(2)Ga(8) show mixed or intermediate valent behavior, and PrRu(2)Ga(8) follows the Curie-Weiss law with no magnetic order down to 4 K.