Increasing Yb Content Research Articles

Enhancement of electrical transport through the anisotropic nanostructure performance of heavily Yb-doped PbSe0.2Te0.8 thin films

Solid-state microwave-assisted plasma technique was used to synthesize high-purity Pb1−xYbxSe0.2Te0.8 from initial components to obtain polycrystalline ingots with large grains. Pb1−xYbxSe0.2Te0.8 thin films were then deposited onto glass substrates using thermal evaporation in vacuum. The films have the polycrystalline rock salt-type (NaCl) structure. The crystal lattice parameters for the powders and thin films obtained from X-ray diffraction (XRD) patterns showed that the values of the lattice parameters increased with increasing Yb content. The field emission scanning electron microscopy images reveal that the Pb1−xYbxSe0.2Te0.8 thin films have uniform crystal grain sizes and dense nanostructures. The electrical transport properties of the thin films were measured in the temperature range of 298 K–523 K. The Seebeck coefficient of the films increased with x when x was in the range of 0.015–0.045, whereas it decreased for x between the range of 0.06 and 0.105. The carrier concentration was 4.3 × 1017 cm−3 for x = 0.015, and the maximum value was 6.34 × 1017 cm−3 at x = 0.075.

Structure transformations and reducibility of nanocrystalline Ce1−xYbxO2−(x/2) mixed oxides

This work presents results of multitechnique (HRTEM, EDX, XRD, XPS, ICP, BET and EELS) studies on structure evolution of nanocrystalline ceria-based Ce1−xYbxO2−(x/2) mixed oxides with increasing Yb content. Nano-sized (∼5nm) mixed oxides were prepared by precipitation in water-in-oil (W/O) microemulsion method. No phase separation or/and segregation were observed for studied samples after heating in oxygen up to 950°C. Realistic models of the intermediate structures (defected F- and C-type) for mixed oxides and mechanism of CeO2→Ce1−xYbxO2−(x/2)→Yb2O3 structural changes have been proposed and tested (HRTEM images and diffraction patterns simulation). Reducibility of Ce1−xYbxO2−(x/2) mixed oxides and its changes with increasing of Yb content was measured and correlated with the structure features. The highest reducibility of Ce ions was observed for Ce0.5Yb0.5O1.75, which has a structure intermediate between F and C-type, with maximum number of defects and the highest average strain.

Effect of ytterbium doping on the microstructure and plastic deformation of BaCeO3 perovskite oxide

Trivalent cation-doped barium cerate perovskites are attractive materials for clean-energy applications, in particular solid oxide fuel cells, due to their singular proton conductivity in wet environments. Furthermore, these devices operate at high temperatures, where creep and other deformation processes determine the lifetime and overall performance. In this work, the structural and microstructural characteristics of undoped and ytterbium-doped (1 to 10at.%) BaCeO3 polycrystals produced by solid state reaction have been investigated. A single orthorhombic perovskite phase was found after sintering in air at 1500°C for 10h. The microstructure shows a complex evolution with doping: the average grain size firstly decreases with increasing Yb content up to 5at.%, and then increases with further Yb additions. The high-temperature mechanical properties have been studied in compression between 1100 and 1250°C in air at constant initial strain rate. The creep strength increases with increasing Yb content. Extended steady states of deformation were attained at lower strain rates and higher temperatures when increasing doping amount.

Hot Corrosion of (Sm1−xYbx)2Zr2O7 (x=0, 0.5, 1.0) Ceramics Against V2O5 Molten Salt in Air at 800°C

(Sm1−xYbx)2Zr2O7 (x=0, 0.5, 1.0) powders synthesized by chemical‐coprecipitation and calcination method were pressureless‐sintered at 1700°C for 10 h in air. Molten V2O5 reacts with (Sm1−xYbx)2Zr2O7 to form m‐ZrO2 and rare‐earth vanadates at 800°C. The thickness of corrosion scales was investigated to evaluate the hot corrosion resistance of (Sm1−xYbx)2Zr2O7. The hot corrosion resistance of (Sm1−xYbx)2Zr2O7 against molten V2O5 increases with increasing Yb content. The hot corrosion mechanisms were proposed based on phase diagrams and the difference in hot corrosion resistance was discussed on terms of basicity of (Sm1−xYbx)2Zr2O7 ceramics.

Dielectric and Piezoelectric Properties of (1-x)(0.36BiScO3-0.64 PbTiO3)-xBiYbO3 Ceramics

(1-x)(0.36BiScO3–0.64PbTiO3)-xBiYbO3 (BSYPTx) piezoelectric ceramics were synthesized by the conventional mixed oxide ceramic processing. The Curie temperature of samples was found in the range from 435°C to 454°C due to the addition of 0.02 ∼ 0.14 mol% BiYbO3. The piezoelectric coefficient d 33 of BSYPTx ceramics decreased with increasing Yb content, exhibiting good piezoelectric properties (d 33 = 443 pC/N and k p = 0.54) at x = 0.02. The coercive field (E c) for BSYPTx ceramics at x = 0.02 was 2.86 kV/mm, increasing to 3.19 kV/cm with the addition of Yb content to x = 0.14.

The synthesis and thermoelectric properties of Yb/Sr double-atom-filled YbxSr8－xGa16Ge30 type-I clathrates

n-type Yb/Sr double-atom-filled YbxSr8-xGa16Ge30 (x=0, 05, 10, 15) clathrates have been synthesized by combining melting reaction with the spark plasma sintering (SPS) method. The effects of double-atom filling on thermoelectric properties have been investigated. The results show that the solubility limit of Yb in the Sr-Ga-Ge system is between 10 and 15 when it is expressed by the formula of YbxSr8-xGa16Ge30. With increasing Yb content x, the room-temperature carrier concentration of the YbxSr8-xGa16Ge30 samples increases, while the room-temperature carrier mobility decreases. For the double-atom-filled samples, the electrical conductivity raises with increasing x, while the Seebeck coefficient reduces, and in which the x=05 sample has a comparable electrical conductivity and a remarkably higher Seebeck coefficient compared with the single-atom-filled Sr8Ga16Ge30 sample in the temperature range of 300—800 K. The double-atom filling of Yb/Sr has significant influence on the lattice thermal conductivity of the YbxSr8-xGa16Ge30 samples and the lattice thermal conductivity decreases gradually with increasing x. Of all the YbxSr8-xGa16Ge30 samples, the maximum dimensionless figure of merit ZT of 081 is obtained at 800 K for the Yb10Sr70Ga16Ge30 sample. Compared with that of single-atom-filled Sr8Ga6Ge30 sample, it is 35% higher at the same temperature.

Electrical Properties of Yb-Doped BaTiO3

The equilibrium electrical conductivity of Yb-doped BaTiO3 was studied as a function of oxygen partial pressure P(O2) and Yb content. The conductivity minimum shifted to lower oxygen partial pressure as the Yb content increased. XRD analysis revealed that the solid solution of Ba(Ti1-xYbx)O3-x/2 was formed without any extra phases (x≤5 mol %). The tetragonality of Ba(Ti1-xYbx)O3-x/2 decreased with increasing Yb content and completely switched to a cubic structure at ≥3 mol %. Lattice constants of Ba(Ti1-xYbx)O3-x/2 increase with increasing Yb content. The Curie point (Tc) shifted to lower temperatures with increasing Yb content. Dielectric constants near the Curie temperature (Tc) were markedly suppressed in the specimens with ≥3 mol % Yb, where the crystal structure was confirmed to be cubic.

High temperature thermoelectric transport properties of double-atom-filled clathrate compounds YbxBa8−xGa16Ge30

Type-I clathrates YbxBa8−xGa16Ge30 (x=0–1.3) filled by ytterbium and barium were synthesized by melting reaction method combined with spark plasma sintering method. The structure and thermoelectric properties of double-atoms-filled clathrate compounds are investigated. X-ray diffraction patterns and Rietveld analysis reveal that the compounds prepared by this method are type-I clathrates. The filling atoms exhibit atomic displacement parameters that are larger than that of framework atoms. All specimens show n-type conduction and the room temperature carrier concentration (Np) increases with the increasing Yb content. The electrical conductivity of the compounds increases at first and then decreases with the increasing Yb content. When x=0.7, it reaches the maximum. The Seebeck coefficient decreases gradually with the increasing x. The substituting of Yb atoms for Ba leads to significant influence on the lattice thermal conductivity of the compounds. The lattice thermal conductivity decreases gradually with the increasing x. Of all the YbxBa8−xGa16Ge30 compounds, Yb0.5Ba7.5Ga16Ge30 compound has the greatest ZT value and its maximal ZT value reaches 1.1 at about 950K. Compared with the Ba8Ga16Ge30 sample, it increases by 90% at the same temperature.

Effect of rare earth Yb addition on mechanical properties of Al–5·3Cu–0·8Mg–0·6Ag alloy

The precipitation hardening response, microstructure and mechanical properties of three Al–5·3Cu–0·8Mg–0·6Ag based alloys containing 0, 0·15 and 0·25 wt-%Yb were investigated using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. It is shown that increasing Yb content from 0 to 0·25 wt-% increased the tensile strength at all test temperatures up to 300 °C. The high strength of the alloys with Yb is attributed to the high density and high thermal stability of fine Ω precipitates.

Mechanical and tribological properties of Nd- and Yb-SiAlON composites sintered by hot isostatic pressing

Single phase α-, β- and two phases α/β-sialon composites were sintered with both Nd 2O 3 and Yb 2O 3 by hot isostatic pressing (HIP). The mechanical and tribological properties of these composite ceramics have been investigated with respect to their application in direct fuel injection pumps for gasoline engines. Scanning electron microscopy (SEM) was used to analyse the fracture surfaces of sialons following sintering and their worn surfaces after the tribological tests. Microstructural evolution and its change with composition as well as the influence of the microstructural changes on the mechanical and tribological properties have been reported. It has been found that increasing α-sialon phase fraction of the Nd-sialons increases the hardness due to the harder nature of this phase, whereas no significant change in the indentation fracture toughness was observed. Increasing Nd content in these sialons resulted in no significant change in both of the hardness and fracture toughness values. On the other hand, single phase Yb-α-sialons showed a slight decrease in the hardness and a gradual increase in the fracture toughness with increasing Yb content. In a comparative way, it can be seen that Yb-doping gives slightly higher hardness and toughness than Nd-doping. This has been explained by the difference between the cationic radii of Nd 3+ and Yb 3+ and the corresponding ionic field strength. Increased ionic field strength of the Yb 3+ in Yb-sialons resulted in an improvement in their mechanical properties. Tribological tests were performed using a laboratory tribometer with ball-on-plate geometry in reciprocating sliding contact under lubrication with isooctane. Based on the friction and wear data, a relative ranking of the different wear pairs of Nd- and Yb-sialon plates together with a commercial Si 3N 4 plate (used as a reference material) against Si 3N 4 ball was established. Sliding pairs of Yb-doped α-sialon ceramics showed higher friction coefficient and lower wear resistance compared to Nd-doped β- and α/β-sialon composites and the commercial Si 3N 4 ceramic. The lowest friction and the highest wear resistance were measured for the Nd-doped sialon with an α:β-ratio of 88:12. SEM micrographs of the worn surfaces revealed that the main wear mechanisms were microabrasion and tribochemical reactions that resulted in the formation of a thin tribolayer composed of compact wear debris in the tribocontact.

Ionic and electronic conductivity of Yb 2+ xTi 2− xO 7− x/2 materials

Bulk and grain boundary conductivities of Yb 2+ x Ti 2− x O 7− x/2 ( x = 0, 0.1, 0.18 and 0.29) materials were studied by impedance spectroscopy in the range 300–900 °C in air. Ionic and electronic conductivities were separated by both ion blocking Hebb–Wagner measurements and total conductivity measurements as a function of oxygen partial pressure in the temperature range 700–1000 °C. The oxygen partial pressure dependence of the total conductivity shows that these materials are nearly pure ionic conductors in air and that the ionic conductivity decreases for Yb-rich compositions. This was interpreted as a predominant effect of a decrease in mobility of ionic charge carriers, opposing the expected increase in concentration of oxygen vacancies with increasing Yb content. The studied materials become mixed conductors under typical fuel conditions, except possibly at temperatures below about 700 °C. Yb-excess slightly suppresses the electronic conductivity.

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.

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.

Preparation and characterization of n- and p-type ytterbium doped InP epitaxial layers

In this paper we pursue the effect of ytterbium (Yb) addition on the physical properties of liquid phase epitaxially (LPE) grown thin InP layers. A series of InP layer samples were prepared by LPE from melts containing 0–0.4 wt% of Yb. The grown layers were examined by Hall effect and C-V measurements, photoluminescence (PL) spectroscopy, and Rutherford backscattering spectrometry (RBS). We have found that Yb impurity was incorporated into the lattice of InP layer. With increasing Yb content in the growth melt the layer’s conductivity smoothly changed from n- to p-type when the Yb admixture exceeded a certain limit. On the basis of these results we prepared p-n junctions in the InP layers directly doped by Yb, and tested them by C-V measurements.

Preparation and properties of Er and Yb doped InP-based semiconductor compounds

In this paper we pursue the effect of the erbium and ytterium addition during the liquid phase epitaxial (LPE) growth on physical properties of thin InP layers. Series of InP layer samples were prepared by LPE from the melts containing 0–0.3 wt.% of Er and Yb. The grown layers were examined by the Hall effect andC-V measurements, photoluminescence spectroscopy and Rutherford backscattering spectrometry (RBS). We have found that only Yb impurity was incorporated into the lattice of InP layer. With increasing Yb content in the growth melt the layer’s conductivity smoothly changed from n to p type when Yb admixture exceeded certain limit. On the basis of these results we prepared p-n junctions in the InP layers directly doped by Yb, and tested then byC-V measurements.

Semiconducting Molybdenum Pyrochlores for high Temperature Applications

ABSTRACTThe solid solutions (Y1-xYbx)2Mo2O7 were prepared and the systematic changes in the electrical resistivity (ρ=l/σ), thermopower (S) and power factor (S2σ) have been studied in the temperature range 300–900 K. The lattice parameters ‘a’ and ‘c’ are smaller for higher Yb3+ content phases due to smaller Yb3+ radius and a small tetragonality is observed for all the phases. Semiconducting behaviour is seen for all compositions with systematic increase in activation energy with increasing Yb content. All compositions show negative thermopower indicating electrons are the majority charge carriers in the temperature range of measurements. The calculated power factor values S2σ increase with increasing temperature in the low temperature region and a maximum power factor of ∼0.76×10−7 Wcm−1K−2 is observed at 650K.