Solubility Of Yb Research Articles

Electronic Structure and Phase Stability of Yb-Filled CoSb3 Skutterudite Thermoelectrics from First-Principles

Filling the large voids in the crystal structure of the skutterudite CoSb$_3$ with rattler atoms $R$ provides an avenue for both increasing carrier concentration and disrupting lattice heat transport, leading to impressive thermoelectric performance. While the influence of $R$ on the lattice dynamics of skutterudite materials has been well studied, the phase stability of $R$-filled skutterudite materials and the influence of the presence and ordering of $R$ on the electronic structure remain unclear. Here, focusing on the Yb-filled skutterudite Yb$_x$Co$_4$Sb$_{12}$, we employ first-principles methods to compute the phase stability and electronic structure. Yb-filled CoSb$_3$ exhibits (1) a mild tendency for phase separation into Yb-rich and Yb-poor regions and (2) a strong tendency for chemical decomposition into Co--Sb and Yb--Sb binaries (i.e., CoSb$_3$, CoSb$_2$, and YbSb$_2$). We find that, at reasonable synthesis temperatures, configurational entropy stabilizes single-phase solid solutions with limited Yb solubility, in agreement with experiments. Filling CoSb$_3$ with Yb increases the band gap, enhances the carrier effective masses, and generates new low-energy ``emergent'' conduction band minima, which is distinct from the traditional band convergence picture of aligning the energies of existing band extrema. The explicit presence of $R$ is necessary to achieve the emergent conduction band minima, though the rattler ordering does not strongly influence the electronic structure. The emergent conduction bands are spatially localized in the Yb-rich regions, unlike the delocalized electronic states at the Brillouin zone center that form the unfilled skutterudite band edges.

PHASE EQUILIBRIA IN THE ZrO2–Yb2O3 SYSTEM AT 1100 °С

Phase equilibria in the binary ZrO 2 – Yb 2 O 3 system at 1100°C were studied by X-ray diffraction and petrography in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcinations at 1100oC. To study phase relationships at 1100°C the as-prepared samples were thermally treated in the furnace with heating elements based on Fecral (H23U5T) at 1100°C (for 12415 in air). The heating rate was 3.5°C/min. It was established that in the ZrO 2 –Yb 2 O 3 system there exist fields of solid solutions based on cubic (C) modifi cation of Yb 2 O 3 , tetragonal (T) crystal modifications of ZrO2, cubic modifi cation of ZrO 2 with fluorite-type structure (F) and δ-phase of Yb 4 Zr 3 O 12 which are separated by wide two phase fields (F + T) and (F + δ) and (δ+C). The boundaries of the homogeneity fi eld for C-Yb 2 O 3 solid solutions were determined from samples containing 80-100 mol % Yb 2 O 3 at heat treatment 1100°C (12415 h). The lattice parameter of the unit cell decreased from а = 1.043 nm in pure Yb 2 O 3 to а = 1.0402 nm for sample containing 25 mol % ZrO 2 - 75 mol % Yb 2 O 3 . The solubility of Yb 2 O 3 in the T-ZrO 2 is low and amounts to 0.5 mol%, as evidenced by XRD analysis results. It is the solid solutions based on tetragonal modification of zirconia cannot be quenched from high temperatures due to low stability of T-ZrO 2 under cooling with furnace conditions. The diffraction patterns recorded at room temperatures included the peaks of monoclinic phase M-ZrO 2 was found. The homogeneity fi eld of F-ZrO 2 in the concentration range of 85-75 mol % ZrO 2 at 1100 °C was established. The lattice parameters of the unit cell increased from а = 0.5124 nm for sample containing 85 mol % ZrО 2 -15 mol % Yb 2 O 3 to а = 0.5152 nm the two-phase (F+δ) sample containing 75 mol % ZrО 2 -25 mol % Yb 2 O 3

Local structure investigation of Ga and Yb dopants in Co4Sb12 skutterudites

We report comprehensive x-ray absorption spectroscopy studies at both the Ga $K$ edge and Yb ${L}_{2}$ edge to elucidate the local structure of Ga and Yb dopants in ${\mathrm{Yb}}_{x}{\mathrm{Ga}}_{y}{\mathrm{Co}}_{4}{\mathrm{Sb}}_{12}$. Our extended x-ray absorption fine structure (EXAFS) data confirm that Ga atoms occupy two crystallographic sites: one is the $24g$ site replacing Sb, and the other is the $2a$ site in the off-center void position. We find that the occupancy ratio of these two sites varies significantly as a function of the filling fraction of additional Yb, which exclusively occupies the $2a$ on-center site. At low concentrations of Yb, ${\mathrm{Ga}}_{24g}$ and ${\mathrm{Ga}}_{2a}$ dopants coexist and they form a charge-compensated compound defect proposed by Qiu et al. [Adv. Funct. Mater. 23, 3194 (2013)]. The ${\mathrm{Ga}}_{24g}$ occupancy increases gradually with increasing Yb concentration, and almost all Ga occupies the $24g$ site for the highest Yb concentration studied ($x=0.4$). In addition to the local structural evidence provided by our EXAFS data, we also present x-ray absorption near-edge structure (XANES) spectra, which show a small Ga $K$-edge energy shift as a function of Yb concentration consistent with the change from predominantly ${\mathrm{Ga}}_{2a}$ to ${\mathrm{Ga}}_{24g}$ states. Our result suggests that the increased solubility of Yb in Yb-Ga co-doped ${\mathrm{Co}}_{4}{\mathrm{Sb}}_{12}$ skutterudites is due to the increased ${\mathrm{Ga}}_{24g}$ electron acceptor, and thus provides an important strategy to optimize the carrier concentration in partially filled skutterudites.

Yb3+-Activated inorganic aprotic liquids for diode-pumped lasers

This paper presents experimental data on the solubility of Yb(III) compounds in POCl3–MCl x , SOCl2–MCl x , and SO2Cl2–GaCl3 binary aprotic solvents (where MClx is a Lewis acid). We have measured the absorption and luminescence spectra of Yb3+ in the solutions thus prepared. Liquid POCl3–MCl4–Yb3+ (M = Zr or Sn), SOCl2–GaCl3–Yb3+, and SO2Cl2–GaCl3–Yb3+ gain media with [Yb3+] > 0.2 mol/L and an Yb3+ luminescence quantum yield η > 0.5 for diode-pumped lasers have been prepared for the first time.

On the boron rich phases in the Yb-B system

Two boron rich phases were successfully synthesized by borothermal reduction of Yb oxide under vacuum. For the new boron-poorer phase, the single phase was established at around [B]/[Yb] = 43.3 at 1500°C (Pbam space group; YB50-type; a = 16.5811(5)Å, b = 17.5950(5)Å, c = 9.4647(3)Å; powder X-ray diffraction; Rietveld refinement). The crystal structure of the boron-richer phase ([B]/[Yb] = 56.7) has been elucidated by single crystal X-ray diffraction (Fm3¯c space group; YB66-type; a = 23.3587(6)Å). Powder X-ray diffraction data of the alloy YbB~70 annealed at 1825°C yielded, along with the YB66-type compound (a = 23.3691(2)Å), β-rh B as a secondary phase (R3¯m space group, a = 10.9298(3)Å, c = 23.875(1)Å), for which the solubility of Yb was found to be below 1at%. The Yb atoms in β-rh B occupy the D and E voids. Both YbB43.3 (YB50-type) and YbB56.7 (YB66-type) feature complicated boron atom frameworks which exhibit shorter B-B separations both within and between boron clusters as compared to those observed for prototype structures.

Mechanism of cluster dissolution of Yb-doped high-silica lanthanum aluminosilicate glass: Investigation by spectroscopic and structural characterization

To investigate clusters of Yb ions and the effectiveness of lanthanum co-doping in dispersing and isolating Yb ions in silica glass, Yb-doped high-silica lanthanum aluminosilicate (LAS) glass with compositions Yb2O3Al2O3La2O3SiO2 was prepared by the sol–gel method combined with high temperature sintering. The glass structure and spectroscopic properties of Yb-doped high-silica LAS glass were studied in detail to explore the mechanism of cluster dissolution. 27Al and 29Si solid-state nuclear magnetic resonance (SSNMR) spectra were introduced to study the spatial distribution of the Yb ions in the glass. The spinning sideband patterns of the 27Al and 29Si NMR spectra showed that part of the Yb3+ ions in the vicinity of aluminium atoms transferred to Si ions with increasing La2O3 concentration. The results of two-dimensional hyperfine sublevel correlation (2D-HYSCORE) electron paramagnetic resonance (EPR) spectroscopy led to the conclusion that the vicinity of Yb3+ ions are mostly aluminum atoms for glass doped with Al and aluminum and silicon atoms for glass co-doped with Al and La. It was also found that Yb clusters exist in the form of YbOYb bonds in high-concentration Yb-doped silica glass and that co-doping with La can replace these bonds with YbOLa linkages to reduce the number of Yb3+ pairs. The fluorescence intensity and fluorescence lifetime of Yb increase steadily with increasing La2O3 concentration, which also indicates that the addition of La in silica glass can dissolve the Yb clusters. The results show that co-doping high-silica LAS glasses with La3+ ions is an ideal way to increase Yb solubility and decrease clustering.

Hydrothermal controls on the genesis of REE deposits: Insights from an in situ XAS study of Yb solubility and speciation in high temperature fluids (T < 400 °C)

High pressure-high temperature experiments are used to investigate the effect of temperature, pH and fluid composition on the transport and deposition of REE and provide constraints on the role of hydrothermal fluids in the formation of rare metal deposits. In situ X-ray absorption (XAS) measurements were conducted at 50MPa to determine simultaneously the solubility of Yb compounds (Yb2O3, Yb2Si2O7 and YbPO4) and Yb speciation from 200 to 350–400°C in fluids involving Cl, F and P ligands. Yb concentrations were monitored down to tens of ppm from the height of the absorption edge while XANES and EXAFS analyses were used to refine the aqueous speciation of Yb in the high temperature fluids. The XAS analysis suggests that Yb solubility is retrograde from 200°C and that 10 to 100ppm Yb can be dissolved in acidic fluids (pH<2) at T<400°C, most probably as Yb[(H2O)7,8]3+ species. Increasing pH and adding phosphorus trigger the precipitation of Yb compounds from 200 to 400°C. Hence buffering of acid orthomagmatic fluids and leaching of P from host rocks could be major mechanisms in the development of (H)REE enrichments in magmatic-hydrothermal systems.

Temperature dependent solubility of Yb in Yb–CoSb3 skutterudite and its effect on preparation, optimization and lifetime of thermoelectrics

Although filled skutterudites are actively being developed for automotive waste heat recovery the compositions considered available are limited. Typically synthesis conditions are chosen with slight excess filling element to produce filled skutterudites at the ‘filling fraction limit’, traditionally considered to be a single value that depends only on the elements involved (e.g. filling element, Co/Fe ratio). The filling fraction limit is often debated and thought perhaps to vary with processing method. This work opens up a new dimension of available compositions by showing that the ‘filling fraction limit’ is a thermodynamic quantity that for Yb varies by a factor of 5 depending on annealing temperature and nominal composition. As the filling element controls the electronic doping in these semiconductors this study not only enables optimization of thermoelectric properties using thermodynamic control rather than non-equilibrium processing conditions (reaching zT = 1.3 at 850 K without nanostructures) but it also predicts dopant precipitation effects after extended use. The novel phase diagram approach used here should be easily applied to other ternary thermoelectric materials to uncover similar phenomena. Thus skutterudite material with the optimized thermoelectric composition can be produced from a range of nominal compositions with appropriate annealing.

Microstructures and mechanical properties of extruded Mg–2Sn–xYb (x=0, 0.1, 0.5 at.%) sheets

Abstract Microstructures and mechanical properties of extruded Mg–2Sn–xYb (x = 0, 0.1, 0.5 at.%) sheets were investigated. The grain size of as-cast Mg–2Sn alloy is significantly reduced with increasing Yb concentration. In addition to α-Mg and Mg2Sn phase, some fine Mg2(Sn,Yb) particles are observed in as-cast Mg–2Sn–0.5Yb alloy, but these fine particles are not observed in as-cast Mg–2Sn–0.1Yb alloy due to a high solubility of Yb in Mg matrix. Tensile tests demonstrated that extruded Mg–2Sn–0.5Yb sheet exhibited the highest tensile strength and available elongation to failure at room temperature, while extruded Mg–2Sn–0.1Yb alloy exhibited the highest tensile properties at 100 °C and 200 °C. The difference in the tensile properties of extruded sheets mainly arises from the different strengthening roles of grain refinement, solid solution strengthening and precipitation strengthening of particles.

Electrical and microstructural properties of Yb-doped CeO2

Nanopowdered Ce1−xYbxO2−δ solid solutions (0 ≤ x ≤ 0.2) were synthesized by a self-propagating room temperature synthesis. XRD and SEM were used to study the properties of these materials as well as the Yb solubility in CeO2 lattice. Results showed that all the obtained powders were solid solutions with a fluorite-type crystal structure and with nanometric particle size. The average size of Ce1−xYbxO2−δ particles was approximately 3 nm. Electrochemical impedance spectroscopy for the sintered pellets depicted that it was possible to separate Rbulk and Rgb in the temperature interval of 550–800 °C. The activation energy for the bulk conduction was 1.03 eV and for grain boundary conduction was 1.14 eV. Grain boundary resistivity dominates over the other resistivities. These measurements confirmed that Yb3+-doped CeO2 material had a potential as electrolyte for intermediate-temperature solid oxide fuel cell applications.

Synthesis and thermoelectric properties of rare earth Yb-doped Ba8−xYbxSi30Ga16 clathrates

The potential thermoelectric and magnetic application of clathrate materials with rare-earth doping is the focus of much of the recent research activity in the synthetic material physics and chemistry. A series of clathrate samples with the chemical formula Ba8−xYbxSi30Ga16 (x=0, 0.5, 0.7, 1 and 1.5) were prepared by combining arc melting, ball milling and spark plasma sintering (SPS) techniques. X-ray diffraction and scanning electronic microscopy combined with energy-dispersive X-ray spectroscopy (EDS) analysis showed the dominant phase to be the type-I clathrate. Whereas, X-ray structural refinement and EDS analysis indicated that some Yb atoms enter the clathrate lattice to replace Ba at 2a sites, while other Yb atoms are oxidized as Yb2O3 precipitated around grain boundaries. The solid solubility of Yb into clathrate lattice yielded x∼0.3. Comparative analysis between Yb-doped and Yb-free clathrates showed that the thermal conductivity decreases with Yb-doping. Consequently, thermoelectric figure of merit ZT significantly increased.

Influence of Yb-doping on optoelectrical properties of CdO nanocrystalline films

Yb-doped CdO thin films with different Yb contents were prepared on glass and silicon substrates by vacuum evaporation technique. The effects of Yb-doping on the structural and optoelectrical properties of the host CdO films were systematically studied. The X-ray diffraction study shows that some of Yb3+ ions substituted for Cd2+ and the solubility of Yb in CdO is very limited and may be around ~0.2 at.%. The Yb-doping influences all the optoelectrical properties of CdO. The bandgap of Yb-doped CdO suffers narrowing by about 20% with a very small (0.03 at.%) doping level. The electrical behaviours show that all the prepared Yb-doped CdO films are degenerate semiconductors. Their dc-conductivity, carrier concentration, and mobility increase compared with undoped CdO film. The largest mobility of about 87 cm2/V s was measured for 0.13 at.% Yb-doped CdO film. From transparent-conducting-oxide point of view, Yb is sufficiently effective for CdO-doping.

Solubility study of Yb inn-type skutteruditesYbxCo4Sb12and their enhanced thermoelectric properties

The solubility of Yb in ${\text{Yb}}_{x}{\text{Co}}_{4}{\text{Sb}}_{12}$ was reported to be 0.19 in bulk skutterudites made by melting and slow cooling method. Surprisingly we increased $x$ close to 0.5 by a special sample preparation method: ball mill and hot press. We show that a higher Yb concentration not only increases the power factor due to a higher electron concentration but also reduces the thermal conductivity $k$ because of stronger phonon scattering. In this way, we have achieved a dimensionless thermoelectric figure of merit ZT of about 1.2 at $550\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ in ${\text{Yb}}_{0.35}{\text{Co}}_{4}{\text{Sb}}_{12}$.

The ternary system Yb–Cu–Mg: Isothermal section at 400 °C in the range from 0 to 67 at.% Cu

Phase relations in the ternary system Yb–Cu–Mg have been established for the isothermal section at 400 °C based on X-ray powder diffraction, metallography, SEM and EPMA techniques on about 30 alloys, which were prepared in sealed Ta-crucibles followed by a homogenisation treatment. Phase equilibria in Yb–Cu–Mg are characterized by the absence of Yb solubility in CuMg 2 and of Mg solubility in YbCu 2. In the compositional range 0–67 at.% Cu five ternary compounds were observed in addition to the Cu-rich ternary phase that is already reported in the literature (τ 1-YbCu 9Mg 2). The section Cu 2Mg–YbCu 2 shows an extended homogeneity range for binary Cu 2Mg up to 8 at.% Yb where Mg atoms are substituted by Yb. At increasing Yb-content τ 2-(Yb 1− x Mg x )Cu 2 (ordered variant of the Cu 2Mg-type) forms with a homogeneity region extending from x = 0.45 to x = 0.63. A ternary phase of stoichiometry Yb 2Cu 2Mg (τ 3) was detected, whose crystal structure is still unknown. Three compounds were found to form near the concentration line with 66.7 at.% Yb: τ 4-Yb 4Cu 1− x Mg 1+ x (0 ≤ x ≤ 0.25, Gd 4RhIn-type), τ 5-Yb 23Cu 7Mg 4 (almost stoichiometric, with a unique structure type) and τ 6-Yb 2Cu x Mg 1− x ( x = 0.2, structure still unknown). Atom order in the crystal structures of YbMg 2 and τ 5-Yb 23Cu 7Mg 4 (Yb 23Cu 7Mg 4-type; P6 3/ mmc; a = 1.1866(2); c = 2.34371(5) nm) was determined by direct methods from X-ray single crystal counter data.

Growth and characterization of CdTe:Ge:Yb

Abstract Cadmium telluride (CdTe) crystals and epitaxial layers were grown by the vertical Bridgman method and vapor-phase epitaxy, respectively, to obtain the high-resistive material suitable for X- and gamma-ray detectors. The crystals and layers were doped with Ge at the concentration of 5×10 17 cm −3 and co-doped with the rare element Yb at the concentration range from 1×10 17 to 1×10 19 cm −3 . The CdTe:Ge:Yb samples were studied by the structural and electrical characterization techniques, low-temperature photoluminescence (PL) and cathodoluminescence (CL) spectroscopy and CL imaging. Experimental findings testify that homogeneous crystals and layers of reasonably good structural quality can be grown with the Yb concentration below the value of 5×10 18 cm −3 that is estimated to be the limit for Yb solubility in CdTe:Ge:Yb. These findings seem to be related with the purification effect caused by the interaction of the Yb dopant with the group I residual impurities.

Electronic structure of MBE grown CdYbTe: photoemission studies

The aim of the work is to present the XPS and UPS studies of a new kind of material MBE grown -CdYbTe thin layers. The analysis of the valence band electron states was performed for three samples (with different Yb contents and different crystallographic quality) by means of resonant photoemission based on the electronic transition between Yb 4d–4f shells. Analysis of Cd 3d, Te 3d and Yb 4d core levels made by XPS gave the qualitative information about the samples before and after Argon ion sputtering. The photoemission spectra for the CdYbTe sample containing 5% Yb, which corresponds to the limit of Yb solubility, were compared with the spectra of the CdYbTe sample with 1% Yb. By means of resonant photoemission Ytterbium was found in two charge states Yb(+2) and Yb(+3).

Lattice location and optical activity of Yb in III–V semiconducting compounds

The location of Yb atoms in indium (InP, Ga0.51In0.49P) and gallium (GaAs, Al0.35Ga0.65As, GaAs0.6P0.4) III–V semiconducting compounds was investigated. It has been shown that Yb atoms occupy substitutional lattice positions only in indium compounds. Solid solubility of Yb in InP is of the order of 1020 cm−3, as estimated from Rutherford backscattering spectroscopy (RBS) measurements and is high by a factor of 2.5 than in 50% GaInP alloy. In gallium compounds the substitutional fraction of Yb is much below the detection limit of the RBS method, even in the case of elevated temperature (250 °C) implantation. It is suggested that optical activity of Yb is related to its substitutional location in the lattices and/or to the character of the YbP bond. The reasons for the material dependent behavior of Yb atoms in III–V crystal hosts are discussed.

The ytterbium-gallium system

The ytterbium-gallium system has been investigated by differential thermal analysis, X-ray diffraction and metallographic analysis. Four intermediate phases have been found to exist in this system, namely Yb 2Ga, YbGa, YbGa 2 and YbGa 4. Yb 2Ga and YbGa were not previously known and their crystal structures have been completely determined. The structure of YbGa 2 has been confirmed while for YbGa 4 a slightly different structure, probably derived from the BaAl 4 type, was found in this work. Eutectic points occur at 21.5 at.% Ga (605°C), 53.5 at.% Ga (880°C) and about 99.0 at.% Ga (27°C). No appreciable solid solubility of Yb in Ga or of Ga in Yb has been observed and the four intermediate phases appear to be line compounds.

The Gd-Yb and Lu-Yb phase systems

The Gd-Yb and Lu-Yb phase systems were established by thermal analysis, X-ray diffrac-tion, metallography, electron microprobe and chemical analyses. The solubility of Yb in α-Gd ranges from 6.5 at. pct at 500°C to 19.0 at. pct at 1161°C. The addition of Yb to Gd lowers theβ (bec) to α (hcp) transformation temperature to an inverse peritectic reaction at 20.0 at. pct Yb and 1161°C. The addition of Yb to Gd lowers the melting point of Gd to a monotectic horizontal at 1183°C which extends from 21.0 to 71.0 at. pct Yb. The monotec-tic composition is 49.0 at. pct Yb. The solid solubility of Gd in Yb ranges from 0.2 at. pct at 500°C to 2.3 at. pct at 819°C. The melting point of Yb is raised from 816°C to 819°C by the addition of Gd while the γ (bee) toβ (fee) transformation temperature of Yb is lowered from 796°C to 780°C by the addition of Gd. The solubility of Yb in solid Lu ranges from 6.0 at. pct at 800°C to 15 at. pct at 1530°C. The addition of Yb to Lu lowers the melting point of Lu to a monotectic horizontal at 1530°C which extends from 15 to 90 at. pct Yb. The monotectic composition is approximately 30 at. pct Yb. The solid solubility of Lu in Yb ranges from less than 0.1 at. pct at 500°C to 0.3 at. pct at 817°C. The addition of Lu raises the melting point of Yb to 817°C and also raises theβ (fee) to y (bec) transformation temperature to 798°C.