Yb Substitution Research Articles

Thermoelectric properties of Pr3Rh4Sn13-type Yb3Co4Ge13 and Yb3Co4Sn13 compounds

Crystallographic data and thermoelectric properties (from 240K up to 380K) of Yb3Co4Ge13, Yb3Co4Sn13 compounds and Yb2CeCo4Ge13 and Yb2.3La0.7Co4Ge13 solid solutions are reported. The Seebeck coefficients, electric resistance and thermal conductivity increase monotonically with increasing temperature from 240 to 380K for all the compounds. The Seebeck coefficient is S=14÷27μV/K for Yb3Co4Sn13, and S=−21÷−12μV/K for Yb3Co4Ge13. The substitution of Yb for cerium or lanthanum in Yb3Co4Ge13 shifts the Seebeck coefficient to positive values. The Yb3Co4Sn13 has a maximal ZT parameter from available Pr3Rh4Sn13-type compounds. The ZT parameter of Yb3Co4Sn13 compound increases from 0.006 up to 0.017 with increasing temperature from 240 to 380K.

Enhanced High-Temperature Thermoelectric Performance of Yb14–xCaxMnSb11

The high temperature p-type thermoelectric material Yb(14)MnSb(11) has been of increasing research interest since its high temperature thermoelectric properties were first measured in 2006. Subsequent substitutions of Zn, Al, and La into the structure have shown that this material can be further optimized by altering the carrier concentration or by reduction of spin-disorder scattering. Here the properties of the Yb(14-x)Ca(x)MnSb(11) solid solution series where isovalent Ca(2+) is substituted for Yb(2+) will be presented. Crystals of the Yb(14-x)Ca(x)MnSb(11) solid solution series were made by Sn-flux (x = 2, 4, 6, 8) with the following ratio of elements: (14-x)Yb: xCa: 6 Mn: 11Sb: 86Sn, and their structures determined by single crystal X-ray diffraction. The density of the material significantly decreases by over 2 g/cm(3) as more Ca is added (from x = 1 to 8), because of the lighter mass of Ca. The resulting lower density is beneficial from a device manufacturing perspective where there is often a trade-off with the specific power per kilogram. The compounds crystallize in the Ca(14)AlSb(11) structure type. The Ca substitution contributes to systematic lengthening the Mn-Sb bond while shortening the Sb-Sb bond in the 3 atom linear unit with increasing amounts of Ca. Temperature dependent thermoelectric properties, Seebeck, electrical resistivity, and thermal conductivity were measured from room temperature to 1273 K. Substitution of Yb with Ca improves the Seebeck coefficient while decreasing the thermal conductivity, along with decreasing the carrier concentration in this p-type material resulting in an enhanced thermoelectric figure of merit, zT, compared to Yb(14)MnSb(11).

Influence of Na, Mg and Yb Substitution for Ca in Bi(Pb)-2223 Superconductor

The effect of Ca substitution by Na, Mg and Yb on the structural and transport properties of Bi1.6Pb0.4Sr2Ca2-xMxCu3Oy (M = Na, Mg and Yb) (x = 0.0 and 0.2) superconducting samples have been investigated. The samples were prepared by the coprecipitation (COP) method. The samples were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), electrical resistivity measurement and critical current density. The critical current density (Jc) and transition temperature (Tc zero) of Na, Mg and Yb substituted with x = 0.2 were found to be lower than the pure sample. Tc zero varies between 100 K and 63 K. Mg concentration was found to give the highest Tc zero of 93 K. Tc zero gradually decreased from Mg, Yb to Na corresponding to a small change in the carrier concentration. Jc decreased with Mg, Yb and Na substitution, and it was measured to be 7.4611 A/cm2, 0.0667 A/cm2, 1.4579 A/cm2 and 1.2479 A/cm2 for pure, Na, Mg and Yb substitution, respectively at 60 K. XRD analysis showed that the decrease of the volume fraction for the 2223 phase and increase of the volume fraction for the 2212 phase with substitution of Na, Mg and Yb. The proportion of Bi-2223/Bi-2212 (%) was estimated from 78.13/21.87 for pure to 51.71/48.29 for Na substitution.

Magnetic dynamics in an electron-doped YbB12 condo insulator

Neutron spectroscopy results are presented for electron-doped YbB12-based systems. Electrondoping effects were obtained through the partial substitution of Yb for four-valence Zr, and through the introduction of a small amount of carbon in the boron sublattice of a YbB12 condo insulator. The different character of the original YbB12 gap-type magnetic-excitation-spectrum changes was observed.

Electronic structure andf-orbital occupancy in Yb-substituted CeCoIn5

The local structure and 4$f$ orbital occupancy have been investigated in Ce${}_{1\ensuremath{-}x}$Yb${}_{x}$CoIn${}_{5}$ via Yb ${L}_{\mathrm{III}}$-edge extended x-ray absorption fine structure (EXAFS), Ce and Yb ${L}_{\mathrm{III}}$-edge x-ray absorption near-edge structure (XANES), and angle-resolved photoemission spectroscopy (ARPES) measurements. Yb(III) (4${f}^{13}$) is the hole analog of Ce(III) (4${f}^{1}$). Yb is found to be strongly intermediate-valent in Ce${}_{1\ensuremath{-}x}$Yb${}_{x}$CoIn${}_{5}$ throughout the entire doping range, including pure YbCoIn${}_{5}$, with an $f$-hole occupancy for Yb of ${n}_{f}\ensuremath{\simeq}0.3$ (i.e., Yb${}^{2.3+}$), independent of Yb concentration and independent of temperature down to $T=20$ K. In contrast, the $f$-electron orbital occupancy for Ce remains close to 1 for all Yb concentrations, suggesting that there is no mutual influence on ${n}_{f}$ between neighboring Ce and Yb sites. Likewise, ARPES measurements at 12 K have found that the electronic structure along $\ensuremath{\Gamma}\ensuremath{-}X$ is not sensitive to the Yb substitution, suggesting that the Kondo hybridization of Ce $f$ electrons with the conduction band is not affected by the presence of Yb impurities in the lattice. The emerging picture is that in Ce${}_{1\ensuremath{-}x}$Yb${}_{x}$CoIn${}_{5}$ there are two networks, interlaced but independent, that couple to the conduction band: one network of Ce ions in the heavy-fermion limit, and one network of Yb ions in the strongly intermediate-valent limit. The robustness of the local and electronic structure to doping suggests the absence of charge transfer between the Ce and Yb ions, and may explain the relative robustness of superconductivity for this Ce-site substitution as compared to the In-site substitution.

Synthesis and Properties of BaZr0.1Ce0.7Y02-xMxO3-δ (x = 0, 0.1; M = Dy, Yb) Compounds

The following barium cerate zirconate compounds were prepared by the solid state route: BaZr0.1Ce0.7Y0.2O3-δ, BaZr0.1Ce0.7Dy0.2O3-δ, BaZr0.1Ce0.7Y0.1Dy0.1O3-δ, The powders were attrition milled, pressed and sintered at 1550 °/4 h. X-ray diffraction data of all compositions show the perovskite orthorhombic phase (powders) and the perovskite cubic phase (pellets). Impedance spectroscopy measurements in the 5 Hz-13 MHz frequency range show that Dy may substitute total or partially for Y without noticeable change in the electrical conductivity, whereas the Yb substitution leads to a decrease in the electrical conductivity. The bulk electrical resistivity follows the trend: Yb- < Dy- < Dy-Y- < Yb-Y- < Y-doped barium cerate zirconate sintered ceramics. A detailed scanning probe microscopy analysis of the polished and thermally etched surfaces of the sintered pellets show images of sub-intergranular regions, which are further evidences of the large grain boundary electrical resistivity of barium cerate compounds.

Transport properties of Zintl phase Yb 1– xCa xCd 2Sb 2 at low temperature

We investigated the transport properties of isoelectronic substitution of Yb by Ca for Zintl phase YbCd 2Sb 2 below 300 K. The p-type Yb 1– x Ca x Cd 2Sb 2 (0.2≤ x≤0.8) samples were synthesized via a solid-state reaction followed by suitable cooling, annealing, grinding, and spark plasma sintering (SPS) densification processes. For samples with x=0.2, 0.4, 0.5, 0.6, 0.8, the electrical conductivity, Seebeck coefficient, thermal conductivity, heat capacity and Hall effect measurements were carried out in the temperature range from 1.9 to 300 K. It was found that the Ca substitution effectively lowered the thermal conductivity at low temperature, while the electrical resistivity and the Seebeck coefficient in the compounds were found to increase with increasing Ca concentration. As a result, the dimensionless figure of merit ZT of 0.18 was attained at 300 K for sample with x=0.2.

Optimizing Thermoelectric Efficiency in La3−xTe4 via Yb Substitution

A low temperature, solid state synthesis technique has enabled the production of homogeneous samples of La3−x−yYbyTe4. This allows the substitution of divalent Yb to be utilized to optimize the thermoelectric performance in lanthanum telluride. The addition of Yb2+ changes the electrical transport properties in a manner that can be well understood using valence counting rules and a corresponding change in the Fermi energy. The substitution of Yb2+ for La3+ results in a threefold finer control over the carrier density n, thus allowing the optimum n ∼ 0.3 × 1021 cm−3 to be both predicted and prepared. The net result is an improvement in thermoelectric efficiency, with zT reaching ∼1.2 at 1273 K.

Effect of Yb, Gd, and Nd Substitution at the Sr Site on the Metal–Insulator Transition of the (Bi,Pb)‐2212 System

Resistivity measurements in the temperature range (64–300 K) were used to study the metal–insulator transition (MIT) driven by a change in the carrier concentration of the Bi1.7Pb0.4Sr2Ca1.1Cu2.1Oy [(Bi,Pb)‐2212] system. The carrier‐concentration is changed by substituting rare‐earth (RE) elements (Nd, Gd, and Yb) at the Sr site of (Bi,Pb)‐2212. Results show that at higher levels of RE substitution, MIT occurs in (Bi,Pb)‐2212, during which the resistivity becomes minimum at a particular temperature(Tmin) for a particular doping level. Below this temperature, resistivity increases with a decrease in the temperature and vice versa, showing an insulating and a metallic nature, respectively. This Tmin and the carrier concentration at which MIT occurs depend on the substituted RE.

Zintl phase Yb1−xCaxCd2Sb2 with tunable thermoelectric properties induced by cation substitution

It has been shown previously that the thermoelectric properties of the Zintl phase compound YbCd2Sb2 can be finely tuned via Zn substitution at the Cd-site in the anionic (Cd2Sb2)2− framework. Here we report the results of the investigation of isoelectronic substitution of Yb by Ca. The p-type Yb1−xCaxCd2Sb2 (0.2≤x≤0.8) samples have been synthesized via a solid-state reaction followed by suitable cooling, annealing, grinding, and spark plasma sintering densification processes. In samples with x=0.2, 0.4, 0.5, 0.6, 0.8, the electrical conductivity, Seebeck coefficient, and thermal conductivity measurements have been carried out in the temperature range from 300 to 650 K. It is found that the Ca substitution effectively lowers the thermal conductivity for all samples at high temperature, while it significantly increases the Seebeck coefficient. As a result, the dimensionless figure of merit ZT of 0.96 has been attained at 650 K for samples with x=0.4, while the value is 0.78 for the unsubstituted YbCd2Sb2

Electrical transport and low-field magnetoresistance properties of (La1–xYbx)2/3Ca1/3MnO3 (x=0 to 0·12) ceramics

Colossal magnetoresistance ceramics with the nominal composition of (La1–xYbx)2/3Ca1/3MnO3(x=0 to 0·12) were synthesised, and their electrical transport and magnetoresistance behaviours were investigated. Experimental results showed that the metal–insulator transition temperature TMI of the ceramic is largely dependent on Yb substitution. Electrical resistivity as a function of temperature in zero field, ρ(0,T) gradually increased with Yb content up to x=0·1 but drastically decreased at x=0·12. The metallic region of the ρ(0,T) curve (T<TMI) of all Yb substituted samples was fitted to the model for electron–electron and electron–magnon scatterings while the insulating region was fitted to a model of polaron hopping with lowest activation energy Ea observed at x=0·10. The largest MR effect of 47% was observed at 0·4 T external field for x=0·10. It is suggested that the increase in ρ(0,T) is related to enhanced Jahn–Teller effect while the MR response is due to magnetic changes as a result of the introduction of Yb3+ magnetic ions.

Controllable thermal expansion and phase transition in Yb 2− xCr xMo 3O 12

The thermal expansion and phase transition of solid solutions Yb 2− x Cr x Mo 3O 12 have been investigated by X-ray powder diffraction and differential thermal analysis. The XRD patterns and the results of Rietveld refinement of Yb 2− x Cr x Mo 3O 12 indicate that the solid solution limit was in the composition range of 0.0 ≤ x ≤ 0.4 and 1.7 ≤ x ≤ 2.0. Yb 2− x Cr x Mo 3O 12 (0.0 ≤ x ≤ 0.4) has an orthorhombic structure and exhibits negative thermal expansion between 200 °C and 800 °C. Yb 2− x Cr x Mo 3O 12 (1.7 ≤ x ≤ 2.0) crystallizes in monoclinic below the phase transition and above, transforms to orthorhombic. Both monoclinic and orthorhombic compounds Yb 2− x Cr x Mo 3O 12 (1.7 ≤ x ≤ 2.0) present positive thermal expansion. Orthorhombic Yb 2− x Cr x Mo 3O 12 exhibit anisotropic thermal expansion with the contraction of a and c axes, and the linear thermal expansion coefficients range from negative to positive with increasing chromium content. Partial substitution of Yb 3+ for Cr 3+ exhibits depressed monoclinic to orthorhombic phase transition.

Microstructural and superconducting properties of Yb-substituted (Bi,Pb)-2212 superconductor sintered at different temperatures

The influence of sintering temperature on the microstructure and superconducting properties of Bi 1.7Pb 0.4Sr 1.8Yb 0.2Ca 1.1Cu 2.1O 8+ δ has been investigated. Yb-free (Bi 1.7Pb 0.4Sr 2.0Ca 1.1Cu 2.1O 8+ δ ) and Yb-substituted (Bi 1.7Pb 0.4Sr 1.8Yb 0.2Ca 1.1Cu 2.1O 8+ δ ) superconducting samples are prepared by solid-state synthesis in bulk form. Significant variations in microstructure, critical current density ( J C) and flux pinning properties have been observed for Yb-substituted samples, sintered at different temperatures in the range 846–852 °C. The flux pinning force ( F P) calculated from the field dependant J C values show that the irreversibility lines (ILs) of Yb-substituted samples shift towards higher fields to different extents depending on the sintering temperature. The samples sintered at 846 °C show maximum flux pinning force of 896 kN m −3 and the peak position of F P shifts to higher fields (0.92 T) as against 16 kN m −3 and 0.12 T for the undoped sample sintered at 848 °C. But the self-field J C value of the samples sintered at 846 °C is lower than that of the samples sintered at 852 °C, which show the maximum self-field J C due to improved microstructure. The variation in microstructure followed by very high enhancement of self-field J C, J C– B characteristic and pinning force density due to Yb substitution within a narrow temperature range is of great technological relevance.

Effect of Yb substitution on microstructure, physical and mechanical properties of negative thermal expansion Zr1−xYbxWMoO8−x/2 (x=0–0.05) ceramic

Cubic Zr1-xYbxWMoO8-x/2 (x = 0-0.05) ceramic was first fabricated by a polymorphous precursor transition method. X-ray diffraction experiment indicates that samples with x <= 0.05 are single phase solid solution. The measured bulk density, microstructure, maximal compression strength and Young's modulus are obviously sensitive to Yb substitution level, while none of such sensitivity was found for the lattice parameters, negative thermal expansion coefficients and Vickers hardness. Drilling tests on Zr(0.96)yb(0.04)WMoO(7.98) ceramic indicate good machinability, which is often required for quality and shape control in engineering applications. (C) 2008 Elsevier B.V. All rights reserved.

Kondo effect in the charge-density-wave state ofLu5−xYbxIr4Si10

${\mathrm{Lu}}_{5}{\mathrm{Ir}}_{4}{\mathrm{Si}}_{10}$ is an established charge-density-wave (CDW) compound $({T}_{\mathit{CDW}}=83\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ which undergoes superconducting transition (SC) at low temperatures $({T}_{C}=3.9\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, leading to the coexistence of CDW and SC. On the other hand, ${\mathrm{Yb}}_{5}{\mathrm{Ir}}_{4}{\mathrm{Si}}_{10}$ is a Kondo lattice compound that shows possible CDW transition below $48\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In this study, we explore the influence of small Yb substitution for Lu in the series ${\mathrm{Lu}}_{5\ensuremath{-}x}{\mathrm{Yb}}_{x}{\mathrm{Ir}}_{4}{\mathrm{Si}}_{10}$. Our observations indicate a decrease of both ${T}_{\mathit{CDW}}$ and ${T}_{C}$ with the increase of Yb content, with the evidence of a Kondo-like response below the CDW transition at low temperatures. Thus, one has a unique opportunity to study the Kondo effect in a CDW lattice in this system.

Defect chemistry and dielectric properties of Yb3+:CaTiO3 perovskite

The defect chemistry of Yb3+:CaTiO3 solid solutions has been investigated both theoretically and experimentally. Three different incorporation mechanisms with similar solution energy were predicted for Yb3+ by atomistic simulation: (i) Ca site substitution with Ca vacancy compensation; (ii) Ti site substitution with O vacancy compensation; (iii) simultaneous substitution at both Ca and Ti sites with self-compensation. X-ray diffraction and scanning electron microscopy results strongly support the possibility to realize the above defect chemistries in CaTiO3 by changing the Ca∕Ti ratio to force Yb3+ on the Ca site (Ca∕Ti&amp;lt;1), on Ti site (Ca∕Ti&amp;gt;1), or on both sites (Ca∕Ti=1) according to the calculations. The temperature dependence of the relative dielectric constant (102–105Hz) of ceramics corresponding to predominant Yb substitution either at the Ca site or the Ti site is qualitatively similar to that of undoped CaTiO3. The Curie-Weiss temperature is shifted to more negative values in comparison to CaTiO3, suggesting that the compositions Ca1−3∕2xYbxTiO3 and CaYbxTi1−xO3 are further driven away from the ferroelectric instability. In contrast, the dielectric properties (102–105Hz) of ceramics corresponding to Ca1−x∕2YbxTi1−x∕2O3 are radically different. The relative dielectric constant is increased of about one order of magnitude (2200 at 30K), is almost independent of temperature, with a maximum variation of 20% in range of 20–300K, and shows frequency dispersion above 150K. The loss tangent at 20–300K is &amp;lt;5% for frequencies ⩾1kHz. The possible mechanism for the observed dielectric behavior is discussed.

Phase stability of thermal barrier oxides: A comparative study of Y and Yb additions

Abstract The maximum operating temperature of conventional thermal barrier coatings based on yttria-stabilized zirconia is ultimately limited by de-stabilization of the “non-transformable” t phase, rendering it susceptible to the monoclinic transformation upon cooling. Investigations into alternative thermal barrier oxide compositions suggest that Yb offers superior t stability compared with Y, Sc and larger rare earth cations at the same concentration. The present study sheds light on this behavior by comparing the microstructure evolution of specimens with 7.6 and 11.4 % MO1.5 (M = Y or Yb) heat treated at 1450 °C for times up to 512 h. X-ray diffractometry and transmission electron microscopy revealed that the onset of partitioning occurs at short times but then the compositions of the phases evolve slowly over time until sufficient stabilizer is depleted from the t phase to render it transformable. Substitution of Yb for Y delays the onset of monoclinic formation. Differences in the transformation behavior of the Y and Yb rich phases on cooling provide new insight and suggest refinements to the current thermodynamic models for the binary ZrO2 – MO1.5 systems are needed.

Effects of Zr on the Microstructure and Mechanical Properties of Al-Sc-Yb Alloys

Cast, coarse-grained Al-Sc alloys are interesting candidates for high temperature, creepresistant applications due to the formation of a high number density of nanometer sized Al3Sc precipitates [1]. Upon addition of Yb to Al-Sc alloys, Yb replaces the Sc forming Al3(Sc1-xYbx) precipitates (L12 structure) [2]. The resulting alloys have higher creep resistance due to the larger lattice parameter mismatch between the matrix and precipitate phases as a result of the substitution of Yb for Sc. The precipitates in Al-Sc-Yb alloys form rapidly at 300 C and the coarsening kinetics are not slowed when compared with binary Al-Sc alloys [3]. Additions of Zr to Al-Sc alloys do, however, retard the coarsening kinetics of the Al3(Sc1-xZrx) precipitates [4]. In the present study, Zr is added to an Al-Sc-Yb alloy. The compositions of the alloys studied are Al-0.06Sc-0.02Yb0.02Zr (at.%) and Al-0.06Sc-0.02Yb-0.005Zr (at.%).

Changes in doping state of (Tl, Pb)Sr1212 superconductors with Yb substitution at Sr site

Samples with nominal starting compositions of Tl0.5Pb0.5Sr2−yYbyCaCu2O7 (y=0–0.6) were synthesized using conventional solid-state synthesis method. Temperature dependent electrical resistance measurements on the series showed that the normal state behavior and superconducting properties can be controlled by adjusting Yb concentration to achieve maximum critical temperature (Tc). The best superconducting behavior for the series was observed for Tl0.5Pb0.5Sr1.8Yb0.2CaCu2O7 with onset critical temperature (Tconset) of 105K. Results of critical temperature (Tc) measurements, microstructure investigation using scanning electron microscope (SEM) and powder X-ray diffraction (XRD) analysis are presented. The effects of Yb substitutions are discussed in terms of Tc, Tl1212 phase formation and the concept of average Cu valence.

Refinement of the α‐Phase Area in the Yb‐SiAlON System

The composition and lattice parameters of several Yb‐SiAlON materials are reported. Electron microprobe analysis was used to measure the compositions of each phase, as this technique avoided the peak overlap problems encountered when using energy‐dispersive spectroscopy. A refined set of equations relating the composition of Yb‐α‐SiAlON to its lattice parameters is presented. The amount of oxygen substitution (n value) in α‐SiAlON has an effect on lattice parameters that is almost as strong as the amount of Al and Yb substitution (m value). The α‐SiAlON phase stability region is shown to extend much closer to the Si3N4‐4/3(AlN:Al2O3) line than reported previously.