Yb Substitution Research Articles

EPR and optical studies of LiNbO3:Yb and LiNbO3:Yb, Pr single crystals

Some results of the absorption investigations of LiNbO 3 :Yb 3+ , Pr 3+ (0.8, 0.1 wt.%) and LiNbO 3 :Yb 3+ (1 wt.%) single crystals were made for UV–vis and IR giving evidence on the Yb 3+ location at Li + sites and Pr 3+ location at Nb 5+ sites. Low temperature absorption measurements have shown the presence of low energy phonons responsible for the intensity shape of the main Yb 3+ IR absorption line as a function of the temperature. Raman spectra confirmed the observation. We have observed several paramagnetic centers originating from both isolated Yb 3+ and Yb 3+ ion pairs. The observed spectral features indicate the Yb centers in both crystals exhibit triclinic C 1 symmetry. The temperature dependence of the EPR line intensity and inverse line intensity confirm the presence of coupled Yb 3+ ion pairs besides isolated Yb 3+ ions in both crystals. The EPR line intensity fulfils Curie–Weiss law and yields the antiferromagnetic interaction constant Θ = −0.6 ± 0.3 K and ferromagnetic interaction constant Θ = 2.4 ± 0.1 K for LiNbO 3 :Yb 3+ and LiNbO 3 :Yb 3+ , Pr 3+ samples, respectively. The presence of co-dopant significantly changes properties of LiNbO 3 :Yb 3+ single crystal. The Pr co-dopant forces the substitution of Yb 3+ ions at other possible sites in the host crystal and changes interaction between Yb ion pairs from the antiferromagnetic to ferromagnetic one.

First-Principles Study of Electronic Structure and Thermoelectric Properties for Guest Substituted Clathrate Compounds Ba<SUB>6</SUB>R<SUB>2</SUB>Au<SUB>6</SUB>Ge<SUB>40</SUB> (R=Eu or Yb)

The electronic structure and thermoelectric properties of guest substituted clathrate compounds Ba6R2Au6Ge40 (R ¼ Eu, Yb) are calculated using the full-potential linearized augmented plane wave method based on the density functional theory. The bottom of conduction band for Ba8Au6Ge40 is formed by one relativity dispersive band close to the M point. When the Ba 2a site is replaced by Eu and Yb, the lowest conduction bands at X point shift to lower energy side. The coupling between gusest atom at 2a sites and the host framework becomes weaker with decreasing ionic radii. This multivalley effect in M and X points yields the increase in the density of states near the conduction band edge, resulting in the increase in the Seebeck coefficient for n-type doping. On the other hand, the valence band edge is almost independent of the guests; the f -bands of Eu and Yb are narrow and distant from the band edge. The effect of Eu and Yb substitution on the Seebeck coefficient is small for p-type doping at higher temperature. [doi:10.2320/matertrans.E-MRA2007865]

Physical properties of Lu1− x Yb x Ni2B2C

The Lu1−x Yb x Ni2B2 system exhibits superconductivity at low Yb concentrations (0≤x≤ 0.1), Kondo behaviour at low and moderate Yb concentrations (0≤x≤ 0.34), and heavy fermion behaviour with a non-magnetic ground state at high Yb concentrations. In order to characterize the evolution of these phenomena with x, we have performed dc magnetic susceptibility, electrical resistivity, thermoelectric power, and specific heat measurements on single crystals of Lu1−x Yb x Ni2B2 with various values of x between 0 and 1. The enhanced suppression of T c by Yb substitution, compared to other rare earth substitutions, is consistent with the behaviour of superconducting Kondo systems with T K≫T c when T K decreases with increasing x. The electronic specific heat coefficient γ increases from ∼11 mJ/mol K2 for x=0 to ∼530 mJ/mol K2 for x=1. The curve of the reduced specific heat jump ΔC/ΔC 0 versus T c/T c0, where ΔC 0 and T c0 refer to the LuNi2B2C matrix, does not conform to the BCS theory, but is consistent with the magnetic pair breaking theory of Abrikosov and Gor'kov or the theory of Müller-Hartmann and Zittartz for superconductivity in the presence of the Kondo effect for . This is in agreement with the evolution of the upper critical field H c2 with x, where the slope decreases with increasing x.

Structural and superconducting properties of Bi 1.7Pb 0.4Sr 2 − xYb xCa 1.1Cu 2.1O y system

The structural, electrical and superconducting properties of Bi 1.7Pb 0.4Sr 2 − x Yb x Ca 1.1Cu 2.1O y system has been studied for different Yb concentrations. The samples are prepared by solid state synthesis in the polycrystalline bulk form. Structural analysis by X-ray diffraction, microstructural examination by SEM and measurements of electrical and superconducting properties have been conducted to study the effects of Yb substitution at Sr site. The critical temperature ( T C) and critical current density ( J C) are found to increase drastically with Yb substitution. Maximum values of T C and J C are observed for x = 0.3 and x = 0.2 respectively. The increase in T C and J C is explained due to the substitution effect of Yb 3+ in place of Sr 2+ and consequent change in the hole concentration in the CuO 2 planes. Above the optimum levels T C and J C begin to reduce due to secondary phase formation. A metal–insulator transition originating from the change of carrier concentration is found to occur at higher doping level ( x > 0.5).

Terahertz optical constants of ytterbium-doped yttrium aluminum garnet crystals

Terahertz time-domain spectroscopy has been employed to measure the optical constants of ytterbium-doped yttrium aluminum garnet (YbxY1−x)3Al5O12 (Yb:YAG) crystals for nominal x values of 0.0, 0.1, 0.2, 0.5, 0.8, and 1.0 in the frequency range from 0.2to1.8THz. The real refractive indices for Yb:YAG crystals increase linearly with the concentration of Yb3+. The experimental results can be fitted by the Sellmeier equation. The results imply that the phonon modes of the Yb:YAG crystals shift to lower frequencies with substitution of Yb for Y. The extinction coefficients of the Yb:YAG crystals are smaller than 0.05.

Thermoelectric properties of Na xCo 2O 4 with rare-earth metals doping prepared by polymerized complex method

Polycrystalline (Na 1− y M y ) x Co 2O 4 (M = Dy and Yb; y = 0.01–0.05) samples were synthesized by the polymerized complex method. The effects of partial substitution of rare-earth metals for a Na-site on the thermoelectric properties of Na x Co 2O 4 were investigated. Dy-substituted samples with y = 0.03 and 0.05 showed the decrease in the electrical resistivity compared to the non-substituted sample because of the enhanced c-axis orientation. The power factors of the Dy-substituted samples were higher than that of the non-substituted sample over the entire temperature range investigated (400–1073 K), and the maximum power factor, 1.5 × 10 −3 W/m/K 2, was obtained at 1073 K for the sample with y = 0.05. The Yb-substitution caused the increase in the electrical resistivity and the Seebeck coefficient compared to the non-substituted sample over the entire temperature range, which is considered to be due to the reduction in the carrier density resulted from the Yb substitution for Na-site. The power factor of the sample with y = 0.03 was enhanced over the entire temperature range and the maximum power factor, 1.5 × 10 −3 W/m/K 2 was obtained at 1073 K.

CHARACTERISTIC ASPECTS OF CERAMIC COMPOUNDS CONTAINING YTTERBIUM

This paper presents experimental data obtained by its author on superconductive ceramics of type 1-2-3, with ytterbium as the element of rare earth. Thermal, electric and magnetic analyses are presented. The aim of the paper is to put in evidence the effect of the substitution of Yb or Cu with Ga in the compound YbBa 2 Cu 3 O 7-δ, in order to compare these properties of this compound with other compounds from the same class having Y or Eu as rare earth ions.

Chemical heterogeneity of a crystal built of nanoscale coherently twinned Yb(2-x)(Fe,Ga)(17+2x) polytypes.

An X-ray study of single crystals extracted from an arc-melted Yb-Fe-Ga alloy showed that the diffraction pattern can be modeled by an intergrown crystal that has three sorts of domains: one hexagonal (1, LuFe(9.5) type) and two rhombohedral (2 a and 2 b, PrFe(7) type), the last two twinned by reticular merohedry. Crystals 1 and 2 are essentially polytypes with maximum degree of order (MDO polytypes), built up of nearly identical slabs that are stacked along [001] in ABAB em leader (1). and ABCABC em leader (2). sequences. Structure refinement was performed by a newly developed program that allowed us to refine several structures on a single data set. We found that the hexagonal and rhombohedral domains differ in chemical composition: while 1 shows a higher rate of Yb substitution by Fe(2) dumbbells, 2 shows partial substitution of Fe by Ga. Our observation of the nanoscale phase segregation is supported by latest finding of nonrandom distribution of stacking faults in a similar 2:17 alloy. An unequal distribution of chemical substitutions in 1 and 2 apparently compensates the inherent mismatch of basal plane dimensions of the individual MDO polytypes and thus constrains their cell parameters within the syntaxy. According to our knowledge this is the first example of two chemically distinct polytypes constituting a single crystal, refined on a single set of diffraction data.

Effect of Partial Substitutions of Rare-earth Metals for Na-site on the Thermoelectric Properties of Na<SUB><i>x</i></SUB>Co<SUB>2</SUB>O<SUB>4</SUB> Prepared by the Polymerized Complex Method

Polycrystalline (Na 1 - y M y ) x Co 2 O 4 (M=Nd, Sm, Dy and Yb; y = 0.01 ∼ 0.05) samples were synthesized by a polymerized complex method. The effects of partial substitution of rare-earth metals for a Na-site on the thermoelectric properties of Na x Co 2 O 4 were investigated, and their differences with the sample prepared by a conventional solid-state reaction (SSR) method were evaluated. In case of the Nd, Sm and Dy-substituted samples, each rare-earth metal content in the matrix phase was slightly higher than that of the sample prepared by the SSR method, resulting in the slight increase in the thermoelectric power. Dy-substituted samples with y = 0.03 and 0.05 showed the decrease in the electrical resistivity compared to the non-substituted sample because of the enhanced c-axis orientation. The power factors of the Dy-substituted samples were higher than that of the non-substituted sample over the entire temperature range, and the sample with y = 0.05 showed the maximum power factor value of 1.5 x 10 - 3 Wm - 1 K - 2 at 1073 K. On the other hand, Yb-substituted samples with y ≤ 0.03 were almost single Na x Co 2 O 4 phase. The maximum Yb content in the matrix phase corresponded to y . = . 0.03 from the EDX analysis. The value was remarkably higher than that of the sample prepared by the SSR method. For the Yb-substituted samples with y < 0.03, the c-axis orientation was enhanced with increasing the nominal Yb composition in conjunction with the rise in the lattice parameter, c. The Yb substitution caused the increase in the electrical resistivity and thermoelectric power compared to the non-substituted sample over the entire temperature range, which is considered to be due to the reduction in the carrier density resulted from the Yb substitution for Na-site. The power factor of the sample with y = 0.03 was enhanced over the entire temperature range, and the maximum power factor, 1.5 × 10 - 3 Wm - 1 K - 2 was obtained at 1073 K.

Effects of rare-earth element substitution on magnetostrictive properties of polycrystalline Tb-Dy-Fe alloys

Magnetostrictive properties of (Tb/sub 0.5/Dy/sub 0.5/)/sub 1-x/RE/sub x/Fe/sub 1.9/ (x=0-0.05, RE=Y, Ce, Sm, Gd, Ho, Yb) polycrystalline compounds were studied. Each rare-earth element formed a RE-Fe/sub 2/ Laves compound with a different lattice spacing. Corresponding to this difference, (Tb/sub 0.5/Dy/sub 0.5/)/sub 0.95/RE/sub 0.05/Fe/sub 1.9/ alloys showed a variation in lattice spacing as a result of the substitution of rare-earth elements and the prestress dependence of magnetostriction changed noticeably. In the case of Y, Sm, and Gd substitution, which showed greater lattice spacing than that of the Tb/sub 0.5/Dy/sub 0.5/Fe/sub 1.9/ alloy, the prestress dependence and maximum magnetostriction decreased. On the other hand, in the case of Ce, Ho, and Yb substitution, which showed a decrease in lattice spacing, the conspicuous prestress dependence was the same as that of the Tb/sub 0.5/Dy/sub 0.5/Fe/sub 1.9/ alloy and the maximum magnetostriction was greater than that of the latter alloy.

Derivation of structural restraints using a thiol-reactive chelator

Recognition and identification of protein folds is a prerequisite for high-throughput structural genomics. Here we demonstrate a simple protocol for covalent attachment of a short and more rigid metal-chelating tag, thiol-reactive EDTA, by chemical modification of the single cysteine residue in barnase(H102C). Conjugation of the metal-chelating tag provides the advantage of allowing a greater range of paramagnetic metal substitutions. Substitution of Yb 3+, Mn 2+, and Co 2+ permitted measurement of metal–amide proton distances, dipolar shifts, and residual dipolar couplings. Paramagnetic-derived restraints are advantageous in the NMR structure elucidation of large protein complexes and are shown sufficient for validation of homology-based fold predictions.

Effect of partial substitution of Yb on valence transition of YbInCu 4

Pure and Yb-site partially substituted by Y, Lu and Zr samples of YbInCu 4 were synthesized. Temperature dependence of magnetic susceptibility from 2 to 300 K under 0.5 T and high field magnetization up to 41 T at 4.2 K were measured. We found that both transition temperature ( T v) and transition magnetic field ( H v) of YbInCu 4 are shifted to lower temperatures and lower magnetic fields by Y or Lu substitution, while they are increased by Zr substitution. The chemical pressure effect and dense Kondo interaction are discussed as factors to influence the valence transition of YbInCu 4.

Thermal Expansion and Electroabsorption in the TlInS2–TlYbS2 System

The thermal expansion and electroabsorption of TlIn1 – xYbx S2 solid solutions were measured as a function of temperature. The introduction of Yb into TlInS2 was found to fully suppress the phase transition. It is shown that there is a perfect correlation between the band gap and thermal expansion of the TlIn1 – xYbx S2 solid solutions: both decrease with increasing Yb content. This finding is interpreted in terms of the effect of Yb substitution on bond strength.

Defects and protons in the CaZrO 3 perovskite and Ba 2In 2O 5 brownmillerite: computer modelling and EXAFS studies

Atomistic computer modelling techniques are used to investigate the substitution of dopants in the CaZrO 3 perovskite and the incorporation of protons in the Ba 2In 2O 5 brownmillerite. The defect calculations on CaZrO 3 predict that small trivalent cations show Zr-site selectivity with oxygen vacancy compensation, while larger cations show Ca-site selectivity with Ca vacancy compensation. EXAFS experiments on doped CaZrO 3 demonstrate Yb and Nd substitution at Zr and Ca sites, respectively, in agreement with the simulations. Finally, several water incorporation reactions in Ba 2In 2O 5 have been examined, including mechanisms involving oxygen interstitial sites.

Magnetostriction enhancement in Laves compounds (Sm,Yb)Fe 2

The magnetic and magnetostrictive properties of compounds (Sm 1− x Yb x )Fe 2 (0⩽ x⩽0.3) have been studied. When x<0.15, the compounds crystallize in the cubic structure of a C15 MgCu 2-type Laves phase. For x>0.15 a small amount of (Sm,Yb)Fe 3 compound with a PuNi 3-type structure appears and its amount increases with increasing Yb content. The magnetic ordering of 1 : 2 compounds is slightly strengthened by the substitution of Yb for Sm. Lattice parameters for Laves phase compounds keep almost unchanged for the whole range investigated, indicating the deviation from Vegard's law linear variation with composition. A magnetostriction enhancement of about 15% when x=0.05% both in spontaneous and polycrystalline magnetostrictions in Sm 0.95Yb 0.05Fe 2 has been observed, which can be ascribed to the anisotropy compensation effect.

Stabilization of high temperature tysonite type compounds in the Sr-Yb-F system-synthesis and Rietveld refinement

Several compositions of the type Sr xYb 1-xF 3-x (x = 0.20, 0.25, 0.30. 0.33) were prepared by heating the well ground mixtures of appropriate amounts of SrF 2 and YbF 3 at 1100°C. The substitution of Yb 3+ in YbF 3 by Sr 2+ for x = 0.25 and 0.3 leads to new single phasic fluorides with tysonite type structure. Quenching was shown to be essential to stabilize these phases. The XRD pattern of Sr 0.25Yb 0.75F 2.75, i.e., SrYb 3F 11 was fitted on a hexagonal unit cell with space group P6 3/mmc with a = 3.9606(4) and c = 6.9731(5) Å. According to Rietveld refinements the as prepared SrYb 3F 11 crystallizes in the disordered HT-form of the tysonite type structure. The magnetic measurements of Sr 0.25Yb 0.75F 2.75 show paramagnetic behaviour with a magnetic moment of 4.6 μ B which corresponds to the f 13 configuration of Yb 3+.

希土類元素置換されたＴｂ‐Ｄｙ‐ＲＥ‐Ｆｅ系ラーベス相化合物の構造と磁歪特性

The structures and magnetostrictive properties of (Tb0.5Dy0.5)1-xRExFe2 compounds (x = 0-0.05, RE = Y, Ce, Sm, Gd, Ho, Yb) were investigated. Each rare earth element was present as a solid solution in Laves phase and caused changes in the lattice spacing. In the cases of Y, Sm, and Gd substitution, which resulted in a wider lattice spacing than that of Tb0.5Dy0.5Fe2 compounds, the prestress dependence and maximum magnetostriction decreased. On the other hand, in the cases of Ho and Yb substitution, which decreased the lattice spacing, a conspicuous prestress dependence existed in the same way as for Tb0.5Dy0.5Fe2 compounds, and the maximum magnetostriction was greater than for those compounds.

Effect of rare-earth (Eu, Yb and Ag) substitutions on superconducting properties of the Bi1.7Pb0.3 Sr2Ca2-xRx(R = Eu, Yb, and Ag)Cu3OY system

The superconducting properties of Bi1.7Pb0.3Sr2Ca2−xRx(R = Eu, Yb and Ag)Cu3OY have been investigated by X-ray diffraction, electrical resistance and the peritectic transition of these superconductors was studied kinetically under different atmospheres and temperature gradients. X-ray diffraction results show that the volume fraction of the high-Tc (2 2 2 3) phase decreases and that of the low-Tc (2 2 1 2) phase increases as Eu, Yb and Ag concentrations increase. The resistivity measurements reveal that the Tc onset decreases down to 100 K for Eu, 85 K for Yb and 106 K for Ag concentrations. These results are explained on the basis of possible variations of hole concentration with trivalent rare earth ion substitutions. Activation energies and frequency factors for crystallisation were determined by non-isothermal differential thermal analysis (DTA), employing different models. It was found that both peritectic transition and reaction rate were dependent on the ambient atmosphere. Kinetic studies under different atmospheres revealed that the thermal stability of Bi-2 2 1 2 phase was greatly enhanced under oxygen atmosphere.

Improved second-harmonic generation by selective Yb ion doping in a new nonlinear optical crystal YCa/sub 4/O(BO/sub 3/)/sub 3/

We describe experiments characterizing a new nonlinear optical crystal, YCa/sub 4/O(BO/sub 3/)/sub 3/ (YCOB). This crystal has a number of advantages over other commonly available nonlinear optical crystals. It has a higher nonlinear coefficient than KDP, can be fabricated to large sizes (/spl sim/3-in diameter, 8-in length), and has a high damage threshold. Moreover, this new nonlinear optical crystal is nonhygroscopic, has good optical quality and mechanical properties, allowing easy optical polishing. This crystal, YCa/sub 4/O(BO/sub 3/)/sub 3/, commonly termed YCOB, is one of a family of new nonlinear crystals, the oxyborates, that include RECa/sub 4/O(BO/sub 3/)/sub 3/ (RE=La/sup 3+/, La/sup 3+/, Y/sup 3+/, Sm/sup 3+/, Gd/sup 3+/, Er/sup 3+/, and Nd/sup 3+/). In this paper, we also successfully demonstrate a technique for improving the nonlinear optical properties of this crystal. This technique, ion substitution, has previously had limited success with other crystal hosts. However, the inclusion of yttrium in YCOB provides the opportunity to exploit this technique. Yb/sup 3+/, which has larger mass, but approximately the same atomic size as Y/sup 3+/ can be substituted into the crystal structure without introducing stress and nonuniformities. A systematic investigation of the linear and nonlinear characteristics of several crystals doped with various levels of Yb demonstrate that selective substitution of Yb in YCa/sub 4/O(BO/sub 3/)/sub 3/ improves the second-harmonic conversion efficiency by increasing the optical nonlinearity.

Suppression of Tc in YbNi 2B 2C and Y 0.9Yb 0.1Ni 2B 2C

Our recent studies have shown that Yb ions are in anomalous magnetic state in YbNi 2B 2C. Though, on the basis of systematic of T c's of superconducting members of RNi 2B 2C (R = rare earth) series, superconductivity is expected to occur in YbNi 2B 2C around 12 K, no superconductivity is found down to 2 K. As superconducting properties of some of the borocarbides are sample dependent, we have investigated off-stoichiometric YbNi 2B 2C with compositions, Yb 1.1Ni 2B 2C, YbNi 1.8B 2C, YbNi 2B 2.2C. We do not find signature of superconductivity down to 2 K in any of these samples. We show here that T c of YNi 2B 2C (∼ 15.5 K) is drastically reduced even at low concentration of Yb; T c of Y 0.9Yb 0.1Ni 2B 2C is ∼ 2.5 K. This depression of T c is anomalously large compared to that expected on the basis of AG theory, perhaps the largest suppression observed on substitution of Yb in any superconductor, and implies strong 4f-conduction electron hybridization.