Mixed Yb Research Articles

Thermal air-oxidized coating on Yb14−xRExMnSb11 ceramics

A high sublimation rate of Yb14MnSb11 as a promising thermoelectric material at working temperatures is a critical factor for its space power application. In search of a way to suppress the sublimation, an isothermal thermogravimetric procedure under controlled conditions was developed and ability of Yb14MnSb11 doped by trivalent rare-earth elements to form the protective air-oxidized scale was studied. A series of ceramic rods Yb14−xRExMnSb11 with RE = La–Lu (except Ce and Eu) and x = 0.1, 0.3 and 0.4 that is close to the solubility limit was examined. Thermogravimetric curves as a time function of a progressively increasing mass of the rods in dry air at temperatures 773, 873, 973 K were recorded, and the kinetic and energetic characteristics of the oxidation process were calculated for the whole series of the isostructural Yb14−xRExMnSb11 solid solutions. Changes of the oxidation curves were considered in the context of the classic Wagner’s theory, and the general kinetic description of the process was made based on the parabolic model. This thermoanalytical investigation for the row of the isostructural Yb14−xRExMnSb11 compounds provided new vision of the oxidation mechanism and the role of the RE additions in the scale formation. For all these compounds, the oxidation kinetics followed the parabolic rate law and solid-state diffusion was the rate-limiting step for the reaction of a dense scale formation from the mixed Yb–RE oxides.

Fully Efficient Direct Yb-to-Er Energy Transfer at Molecular Level in a Near-Infrared Emitting Heterometallic Trinuclear Quinolinolato Complex

Combined chemical/photophysical studies on the mixed Yb–Er trinuclear lanthanide quinolinolato compound Yb2ErQ9 and on the corresponding Yb3Q9 analogue have been performed. In the mixed-metal molecular species, the ligands, acting as a bridge, allow the two metals to lie at optimal distance for direct Yb-to-Er resonance energy transfer, which reaches nearly unitary efficiency. The obtained results show that polynuclear lanthanide complexes provide a suitable strategy for achieving effective erbium sensitization in solution-processable molecular materials.

Growth and laser operation of Yb-doped mixed vanadate crystals

Abstract Three mixed Yb t Y x Lu 1− t − x VO 4 crystals, with x =0.923, 0.848 and 0.708, were grown by the Czochralski method. Polarized absorption spectra and fluorescence spectra were studied at room temperature. The absorption cross sections at 985 nm are 5.46×10 −20 cm 2 , 5.70×10 −20 cm 2 , and 5.97×10 −20 cm 2 , respectively, for π polarization. The broadest bandwidth of the absorption spectrum reaches up to 38.22 nm for σ polarization. Fluorescence lifetimes are almost the same (0.331 ms, 0.327 ms and 0.329 ms). CW laser operation was achieved at room temperature with a maximum output power of 1.19 W at a pump power of 8.8 W.

Determination of Hf isotope ratios in zircon using multiple collector-inductively coupled plasma mass spectrometry equipped with laser ablation and desolvating nebulizer dual sample introduction system

Copyright © 2012 by The Geochemical Society of Japan. tained from Hf, e.g., using 179Hf/177Hf, is not applicable to Yb. Therefore, the use of 171Yb/173Yb is strongly encouraged to estimate the 176Yb intensity (Iizuka and Hirata, 2005; Kemp et al., 2009; Woodhead et al., 2004). However, since the reported isotope ratios for 171Yb, 173Yb, and 176Yb varied between reports, the “appropriate” isotope ratios were rigorously discussed and a consensus was reached (Iizuka and Hirata, 2005; Kemp et al., 2009). Even so, there seems no consensus on how to correct for the interference of 176Yb. The means of 176Yb correction used in recent studies are classified into three types: (1) using a modified 176Yb/172Yb, which yields the correct 176Hf/177Hf for mixed Yb–Hf standard solution using solution MC-ICPMS without obtaining mass bias factor β(Yb) (Griffin et al., 2006); (2) using β(Yb) obtained with reported 173Yb/171Yb and 176Yb/173Yb (Iizuka and Hirata, 2005; Iizuka et al., 2010; Kemp et al., 2009; Thirlwall and Anczkiewicz, 2004); and (3) using β(Yb) and slightly modified 176Yb/172Yb to reproduce accurate values for 91500 and TEMORA zircon standards (Wu et al., 2006). Determination of Hf isotope ratios in zircon using multiple collector-inductively coupled plasma mass spectrometry equipped with laser ablation and desolvating nebulizer dual sample introduction system

Yb Valence States in YbC2: A HERFD-XANES Spectroscopic Investigation

The valence state of Yb in YbC(2) was analyzed using high-energy-resolution fluorescence detection (HERFD) X-ray absorption near-edge structure (XANES) spectroscopy and time-of-flight neutron powder diffraction to clarify a controversy in the literature. The unit cell volume of YbC(2) suggests a mixed Yb valence, which was formerly determined to be 2.8 by magnetization measurements and paramagnetic neutron scattering techniques. However, the nature of the intermediate valence was not clearly established. Both homogeneous and heterogeneous mixed valences were assumed in different publications. The temperature-dependent behavior of the valence state was only predicted, albeit not explicitly studied. In this work, the valence state of Yb in YbC(2) is, therefore, investigated thoroughly by HERFD-XANES spectroscopy at low and high temperatures. Our measurements result in an average Yb valence of 2.81 that is temperature-independent from 15 to 1123 K. These findings are confirmed by neutron powder diffraction experiments, which reveal a constant C-C distance of 128.7(9) pm in a temperature range from 5 to 100 K. A significant temperature dependence of the Yb valence state in YbC(2) can, therefore, be excluded by our experimental results.

Photoelectron spectra of Yb-Si(100) heterointerfaces formed at room temperature

The laws of formation of the heterointerfaces formed upon ytterbium (Yb) deposition at room temperature (T=300 K) onto a (2×1)-reconstructed Si(100) surface were studied by methods of photoelectron spectroscopy (PES) with excitation by synchrotron radiation and low-energy electron diffraction (LEED). In the range of submonolayer surface coverages θ, the adsorption of Yb atoms leads to destruction of the surface dimers. This is accompanied by the formation of an amorphous film consisting of mixed Yb and Si atoms. For θ>1.5, a partly ordered metallic ytterbium film containing dissolved Si atoms is formed on the substrate surface. In all stages of deposition, there is charge transfer from Yb to Si atoms, which is manifested by a shift of the Si 2p core level. This shift is especially pronounced (reaching 1.5 eV) for silicon atoms dissolved in the metallic film.

Pyrochlores. III. X-Ray, neutron, infrared, and dielectric studies of A2Sn2O7 stannates

A number of compositions [Formula: see text] and of related mixed phases were prepared and investigated. For the trivalent lanthanons from La to Lu, and for Y, the homogeneous A2Sn2O7 phases were of the cubic pyrochlore type (space group Fd3m, No. 227). Their lattice parameters gave a very good linear relationship when plotted against the Templeton–Dauben radii of A3+. The applicability of other sets of ionic radii was also tested. The lower limit of the r(A3+):r(Sn4+) ratio for cubic pyrochlore stannates is about 1.19 (Ahrens radii), while the upper limit is at least 1.60. Attempts to extend the lower limit by preparing mixed Yb + Sc stannates were only partially successful. Bi2Sn2O7 is not a cubic pyrochlore.The structures of Y2Sn2O7 and Sm2Sn2O7 were refined from X-ray powder data, and that of La2Sn2O7, from neutron powder data. The positional parameter of the majority oxygen atom, x(O2), has been found to increase with the size of A3+. The distortion of the SnO6 octahedra in the pyrochlore structure thus decreases with increasing r(A3+).From a systematic study of the infrared spectra of the stannates it appears that it is the size of the Y3+ ion rather than its chemistry (as distinct from the Ln3+ ions) that determines its place among the 3–4 pyrochlores. No evidence of ferroelectricity was found in Pr, Er, and Lu stannates between room temperature and 4.2 °K.