Yb Atoms Research Articles

Study of the magnetic properties of YbMn2Sb2 single crystals by [formula omitted]SR

The crystal growth and the structural, transport and magnetic properties of YbMn2Sb2 single crystals are reported. The crystals show a trigonal symmetry of La2O2S-type structure (space group P3¯m1, N. 164, hP5), where corrugated honeycomb layers of MnSb are separated by Yb atoms. No structural phase transition was observed down to 22 K. The resistivity measurements show a predominantly insulating behavior. The combined resistivity, dc susceptibility and specific heat measurements confirm successive features at 40 K, 116 K and 225 K, being the phase transition at TN=116 K due to the Mn+2 lattice antiferromagnetic ordering. Muon spin rotation experiments (μSR) reveal a more complicated scenario, with temperature dependence of the magnetic volume fraction reflecting a static and strongly disordered magnetic ground state. The role of spin–lattice coupling and its relationship with exchange interactions between Mn moments is discussed as a possible cause of the magnetic behavior observed.

Complex Structural Disorder in the Zintl Phases Yb10MnSb9 and Yb21Mn4Sb18.

A systematic investigation of the ternary system Yb-Mn-Sb led to the discovery of the novel phase Yb10MnSb9. Its crystal structure was characterized by single-crystal X-ray diffraction and found to be complex and highly disordered. The average Yb10MnSb9 structure can be considered to represent a defect modification of the Ca10LiMgSb9 type and to crystallize in the tetragonal P42/mnm space group (No. 136) with four formula units per cell. The structural disorder can be associated with both occupational and positional effects on several Yb and Mn sites. Similar traits were observed for the structure of the recently reported Yb21Mn4Sb18 phase (monoclinic space group C2/c, No. 15), which was reevaluated as part of this study as well. In both structures, distorted Sb6 octahedra centered by Yb atoms and Sb4 tetrahedra centered by Mn atoms form disordered fragments, which appear as the hallmark of the structural chemistry in this system. Discussion along the lines of how difficult, and important, it is to distinguish Yb10MnSb9 from the compositionally similar binary Yb11Sb10 and ternary Yb14MnSb11 compounds is also presented. Preliminary transport measurements for polycrystalline Yb10MnSb9 indicate high values of the Seebeck coefficient, approaching 210 μV K-1 at 600 K, and a semiconducting behavior with a room-temperature resistivity of 114 mΩ cm.

Finite-range effects in the two-dimensional repulsive Fermi polaron

We study the repulsive Fermi polaron in a two-component, two-dimensional system of fermionic atoms inspired by the results of a recent experiment with $^{173}$Yb atoms [N. Darkwah Oppong \textit{et al.}, Phys. Rev. Lett. \textbf{122}, 193604 (2019)]. We use the diffusion Monte Carlo method to report properties such as the polaron energy and the quasi-particle residue that have been measured in that experiment. To provide insight on the quasi-particle character of the problem, we also report results for the effective mass. We show that the effective range, together with the scattering length, is needed in order to reproduce the experimental results. Using different model potentials for the interaction between the Fermi sea and the impurity, we show that it is possible to establish a regime of universality, in terms of these two parameters, that includes the whole experimental regime. This illustrates the relevance of quantum fluctuations and beyond mean-field effects to correctly describe the Fermi polaron problem.

INFLUENCE OF YTTERBIUM IMPURITY ON THE GENERATION CHARACTERISTICS OF MDP STRUCTURES

The influence o f ytterbium atoms on the electrophysical properties o f silicon MIS- structures is investigated by means o f CC-DLTS and high-frequency volt- faradic characteristics. It is shown that the presence o f ytterbium atoms in the volume o f the silicon substrate leads to a decrease in the density o f surface states o f MIS - structures. It is found that the presence o f Yb atoms in the substrate does not lead to noticeable changes in the density distribution o f surface states o f Nss over the width o f the band gap Eg

Effect of Yb3+ substitution on the structural and optical properties of Ba1-xYbxWO4 nanoparticles-NIR luminescence emissions for optical communication and bioanalyses

Ba1-xYbxWO4 nanoparticles were synthesized by chemical precipitation route and the effect of Yb3+ substitution on their materials properties were investigated using various characterization tools. The structural properties of the Ba1-xYbxWO4 samples were characterized by X-ray diffraction, Fourier transformed infrared spectroscopy and Raman spectroscopy. Optical properties of the synthesized Ba1-xYbxWO4 nanoparticles were studied using UV–Visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. The structural studies show that Ba1-xYbxWO4 samples have tetragonal scheelite structure. Transmission electron microscopy and scanning electron microscopy analyses confirm that the size and shape of the Ba1-xYbxWO4 nanoparticles changes upon Yb3+ substitution. The optical bandgap of the samples decreases with an increase in the amount of Yb atoms in the Ba1-xYbxWO4 sample, which confirms the formation of intermediate energy levels. Photoluminescence spectra exhibit near infrared emission for the Ba1-xYbxWO4 samples, which proposes their uses in optical fiber communication, efficient solar cells, and bioanalyses and imaging.

Geometric phase of Wannier–Stark ladders in alkaline-earth(-like) atoms

We discuss the geometric phase of Wanner-Stark ladders generated by periodically driven clock states in alkaline-earth(-like) atoms. Using $^{171}$Yb atoms as a concrete example, we show that clock states driven by two detuned clock lasers can be mapped to two-band Wannier-Stark ladders, where dynamics of the system along the ladder is mapped to Bloch oscillations in a one-dimensional topological lattice. When the adiabatic condition is satisfied, the geometric phase accumulated in one period of the oscillation is quantized, and reveals the change of band topology as the laser parameters are tuned. We show how the geometric phase can be experimentally detected through interference between different nuclear spin states. Our study sheds light on the engineering of exotic band structures in Floquet dynamics.

Laser stabilization to neutral Yb in a discharge with polarization-enhanced frequency modulation spectroscopy

Isotope selective optical excitation of atoms is important for experiments with neutral atoms, metrology, and work with trapped ions, including quantum information processing. Polarization-enhanced absorption spectroscopy is used to frequency stabilize a tunable external cavity laser diode system at 398.9 nm for isotope selective photoionization of neutral Yb atoms. This spectroscopy technique is used to measure isotope resolved dispersive features from transitions within a see-through configuration ytterbium hollow-cathode discharge lamp. This Doppler-free dichroic polarization spectroscopy is realized by retro-reflecting a laser beam through the discharge and analyzing the polarization dependent absorption with balanced detection. The spectroscopy signal is recovered using lock-in detection of frequency modulation induced by current modulation of the external cavity laser diode. Here, we show an order of magnitude improvement in the long-term stability using polarization-enhanced absorption spectroscopy of Yb compared to polarization spectroscopy.

Phonons, Q -dependent Kondo spin fluctuations, and 4f phonon resonance in YbAl3

The intermediate valence (IV) compound YbAl$_3$ exhibits nonintegral valence (Yb 4$f^{14-n_f}$ (5d6s)$^z$ where z = 2+n$_f$ = 2.75) in a moderately heavy (m* = 20-30me) ground state with a large Kondo temperature (T$_K$ ~ 500-600K). We have measured the magnetic fluctuations and the phonon spectra on single crystals of this material by time-of-flight inelastic neutron scattering (INS) and inelastic x-ray scattering (IXS). We find that at low temperature, the Kondo-scale spin fluctuations have a momentum (Q) dependence similar to that seen recently in the IV compound CePd$_3$ and which can be attributed to particle-hole excitations in a coherent itinerant 4$f$ correlated ground state. The Q-dependence disappears as the temperature is raised towards room temperature and the 4$f$ electron band states become increasingly incoherent. The measured phonons can be described adequately by a calculation based on standard DFT+$U$ density functional theory, without recourse to considering 4$f$ correlations dynamically. A low temperature magnetic peak observed in the neutron scattering at ~ 30meV shows dispersion identical to an optic phonon branch. This 4$f$/phonon resonance disappears for T > 150K. The phonons appear to remain unaffected by the resonance. We discuss several possibilities for the origin of this unusual excitation, including the idea that it arises from the large amplitude beating of the light Al atoms against the heavy Yb atoms, resulting in a dynamic 4$f$/3$p$ hybridization.

Controlling reaction process to realize high thermoelectric performance in filled skutterudites

Filling Yb atoms into the nanovoid of skutterudites has been long the main strategy to achieve high thermoelectric performance. However, both the ZT and the Yb actual total filling fraction (ATFF) show great discrepancies among the literature. The underlying mechanisms behind such discrepancy still keep mysterious. Here, we theoretically and experimentally study the solid solution and phase transformation in the un-filled, single-filled, and multiple-filled skutterudites from a kinetics perspective. The ZT and ATFF discrepancies are thus explained by the complex reaction process. Our density functional theory calculations indicate that an extraordinarily large energy barrier exists in the solid solution process of Yb atoms in CoSb3.The introduction of other filling atoms can further reduce the Yb diffusion rate, putting off the overall reaction process. As the reaction progresses, the ATFF first increases sharply and finally keeps constant, representing the complex phase transition behaviors from non-equilibrium microstructures to equilibrium microstructures. Through optimizing the synthesis route, we successfully promote the reaction process to the ultimate limit in the Yb0.3Ca0.1Al0.1Ga0.1In0.1Co3.75Fe0.25Sb12 sample. A remarkable theoretical conversion efficiency of 14.12% is achieved, exhibiting excellent stability and reproducibility as expected. Our results provide an intrinsic understanding of chemical doping from materials science essentials, which is applicable for designing other high-performance functional materials.

Superstructure formation in a ternary Yb-Cd-Mg 1/1 quasicrystal approximant

ABSTRACT The superstructure and basic structure of ternary Yb-Cd-Mg 1/1 quasicrystal approximants with the compositions YbCdMg and YbCdMg were investigated using X-ray structural analysis. The former was determined to have a face-centred packing structure comprising two distinguishable Tsai-type rhombic triacontahedron clusters (space group , Å), while the latter was found to have a body-centred packing structure made of identical Tsai-type rhombic triacontahedron clusters (space group , Å). The distinction between the two types of clusters in the superstructure is based on the positional disorder of the first tetrahedron shell and the relative Cd/Mg occupancy at M5 sites in the fourth icosidodecahedron shell. In both the superstructure and basic structure, sites preferentially occupied by Mg typically have two Yb atoms among the atoms to which they are coordinated. Finally, a six-dimensional structural model of the primitive Tsai-type icosahedral quasicrystals was modified so as to incorporate the selective Cd/Mg occupation found in the 1/1 approximants.

Phase development and pore stability of yttria‐ and ytterbia‐stabilized zirconia aerogels

AbstractHigh‐porosity yttria‐ and ytterbia‐stabilized zirconia aerogels offer the potential of extremely low thermal conductivity materials for high‐temperature applications. Yttria‐ and ytterbia‐doped zirconia aerogels were synthesized using a sol‐gel approach over the dopant range of 0‐20 atomic percent. Surface area, pore volume, and morphology of the as‐dried aerogels and materials thermally exposed for short periods of time to temperatures up to 1200°C were characterized by nitrogen physisorption, scanning and transmission electron microscopy, and X‐ray diffraction. The aerogels as supercritically dried all were X‐ray amorphous. At a 5% dopant level, a tetragonal structure with a smaller monoclinic phase developed on thermal exposure. Mixed tetragonal and cubic phases or predominantly cubic materials were observed at higher dopant levels, depending on the dopant level, temperature and exposure time. The formation of crystalline phases was accompanied by loss of surface area and pore volume, although some mesoporous structure was maintained on short‐term exposure to 1000°C. Incorporation of the smaller Yb atom into the lattice structure resulted in smaller lattice dimensions on crystallization than was seen with Y doping and favored a more highly equiaxed structure. Aerogels synthesized with 15% Y maintained the smallest particle size without evidence of sintering at 1100°C. Largest shrinkage and loss of pore volume occurred on crystallization from the amorphous phase, with further loss of pores at temperatures above 1000°C attributable to changes in lattice parameters.

Extended combination rule for like-atom dipole dispersion coefficients.

An extended combination rule is proposed to relate the dipole-dipole dispersion coefficient for the interaction of the like target species to the same coefficients for the interactions between the target and a set of partner species. The rule can be derived either by uniform discretization of the Casimir-Polder integral on a quadrature or by relating the dynamic dipole polarizabilities of the target species and the partner species. Both methods result in the same system of linear equations, whose solution also requires the knowledge of the dispersion coefficients for interaction between the partner species. The test examples indicate a high accuracy of the proposed rule for dispersion coefficients (better than 1% in the stringent test for the Yb atom interacting with a rare gas and alkaline-earth metal atoms). However, the combination rule does not warrant correct approximation of the dynamic polarizability of the target species.

Trapping Yb171 atoms into a one-dimensional optical lattice with a small waist

In most experiments with atoms trapped in optical lattices, the transverse size of the optical lattice beams is on the order of tens of micrometers, and loading many atoms into smaller optical lattices has not been carefully investigated. We report trapping 1500 $^{171}$Yb atoms in a one-dimensional optical lattice generated by a narrow cavity mode at a distance of 0.14 mm from a mirror surface. The simplest approach of loading atoms from a mirror magneto-optical trap overlapped with the cavity mode allows the adjustment of the loading position by tuning a uniform bias magnetic field. The number of atoms trapped in the optical lattice exhibits two local maxima for different lattice depths, with a global maximum in the deeper lattice. These results open a way to quantum mechanical manipulation of atoms based on strong interaction with a tightly focused light field.

Effects of lanthanides doping on the optical properties of graphene/WSe2 heterostructure based on ab-initio calculations

Based on the density functional theory, we discussed the electronic and optical properties of graphene/ WSe2 (GW) heterostructure after lanthanides doping. Red shift appears and the optical parameter values are improved in the low energy region after the lanthanides are doped. Different doping types are also discussed. In the case of single doping, substitute Yb atom on W site will improve the peak values of the optical parameters greatly. In the case of co-doping, it is found that the effect will be more obvious when the two doped lanthanide atoms are located in the second neighboring positons. These results suggest that lanthanides doping does adjust the electronic structure and improve the optical properties of GW heterostructures, which providing useful guidance for the design of novel optical nanodevices based on two-dimensional materials.

Orbital ordering of ultracold alkaline-earth atoms in optical lattices

We report on a dynamical mean-field theoretical analysis of emerging low-temperature phases in multicomponent gases of fermionic alkaline-earth(-like) atoms in state-dependent optical lattices. Using the example of $^{173}$Yb atoms, we show that a two-orbital mixture with two nuclear spin components is a promising candidate for studies of not only magnetic but also staggered orbital ordering peculiar to certain solid-state materials. We calculate and study the phase diagram of the full Hamiltonian with parameters similar to existing experiments and reveal an antiferroorbital phase. This long-range-ordered phase is inherently stable, and we analyze the change of local and global observables across the corresponding transition lines, paving the way for experimental observations. Furthermore, we suggest a realistic extension of the system to include and probe a Jahn-Teller source field playing one of the key roles in real crystals.

HPHT Synthesis: Effects of the Synergy of Pressure Regulation and Atom Filling on the Microstructure and Thermoelectric Properties of Yb x Ba8-x Ga16Ge30.

Type-I clathrate compounds YbxBa8–xGa16Ge30 have been synthesized by the high-pressure and high-temperature (HPHT) method rapidly. The effects of the synergy of atom filling and pressure regulation on the microstructure and thermal and electrical properties have been investigated. With the content of Yb atom increasing, the carrier concentration is improved, the electrical resistivity and the absolute Seebeck coefficient are decreased, while the thermal conductivity is reduced significantly. A series of extremely low lattice thermal conductivities are achieved, attributed to the enhancement of multiscale phonon scattering for the “rattling” of the filled guest atoms, the heterogeneous distribution of nano- and microstructures, grain boundaries, abundant lattice distortions, lattice deformations, and dislocations. As a result, a maximum ZT of about 1.07 at 873 K has achieved for the Yb0.5Ba7.5Ga16Ge30 sample.

Low-Energy Electron Elastic Total Cross Sections for Ho, Er, Tm, Yb, Lu, and Hf Atoms

The robust Regge-pole methodology wherein is fully embedded the essential electron-electron correlation effects and the vital core polarization interaction has been used to explore negative ion formation in the large lanthanide Ho, Er, Tm, Yb, Lu, and Hf atoms through the electron elastic total cross sections (TCSs) calculations. These TCSs are characterized generally by dramatically sharp resonances manifesting ground, metastable, and excited negative ion formation during the collisions, Ramsauer-Townsend minima, and shape resonances. The novelty and generality of the Regge-pole approach is in the extraction of the negative ion binding energies (BEs) of complex heavy systems from the calculated electron TCSs. The extracted anionic BEs from the ground state TCSs for Ho, Er, Tm, Yb, Lu, and Hf atoms are 3.51 eV, 3.53 eV, 3.36 eV, 3.49 eV, 4.09 eV and 1.68 eV, respectively. The TCSs are presented and the extracted from the ground; metastable and excited anionic states BEs are compared with the available measured and/or calculated electron affinities. We conclude with a remark on the existing inconsistencies in the meaning of the electron affinity among the various measurements and/or calculations in the investigated atoms and make a recommendation to resolve the ambiguity.

In situ XAFS study of highly reducible mixed oxide catalysts Ce0.9Pd0.1O2-δ and Ce0.7Yb0.2Pd0.1O2-δ

Abstract Within this paper the simultaneous local structural analysis of the highly reducible mixed oxides catalysts Ce0.9Pd0.1O2-δ and Ce0.7Yb0.2Pd0.1O2-δ is presented under reduction and oxidation conditions at elevated temperatures up to 500 °C. In situ X-ray Absorption Fine Structure characterization shows that during the reduction up to 80 °C no changes are observed in both of the exemplarily studied samples. The oxidation of the Ce1-xPdxO2-δ sample continuously introduces changes in the structure over the whole temperature range while for the Ce0.7Yb0.2Pd0.1O2-δ sample oxidation is completed already at 200 °C. The metallic palladium cluster formation in both studied samples was followed by Extended X-ray Absorption Fine Structure (EXAFS) studies. The presence of the Yb atoms affects the formation time and the Pd cluster size. It was found that during the reduction process the palladium cluster creation is initiated at higher temperatures for the Ce0.9Pd0.1O2-δ sample than for the Ce0.7Yb0.2Pd0.1O2-δ sample. The higher percentage of Pd atoms creates metallic palladium clusters in the Ce0.9Pd0.1O2-δ sample.

Magnetic Properties of theRE2Pt6X15(RE= Y, La–Nd, Sm, Gd–Lu;X= Al, Ga) Series

The members of theRE2Pt6Al15(RE= Ce–Nd, Sm, Gd–Yb) andRE2Pt6Ga15(RE= Y, La–Nd, Sm, Gd–Lu) series have been synthesized from the elements via arc‐melting followed by annealing in an induction furnace. Isotypism of Ho2Pt6Al15with orthorhombic (3+1)D commensurately modulated Sc2Pt6Al15[Cmcm(α,0,0)0s0,α= 2/3] was observed from single‐crystal diffraction data. The diffraction pattern shows the same satellite reflections pattern as the prototype, therefore the same modulated superstructure was refined. Full ordering of the Pt and Al atoms within the [Pt6Al15]δ–polyanion was observed. The lattice parameters of the averaged hexagonal structure were refined from powder X‐ray diffraction experiments and agree well with previous reports on these compounds. The X‐ray pure polycrystalline samples of both series were studied with respect to their magnetic properties. The susceptibility data of all investigated compounds show experimental magnetic moments close to the free ion values of theRE3+cations and antiferro‐/ferrimagnetic ordering at low temperatures with Curie temperatures up toTC= 16.8(1) K for Gd2Pt6Ga15. Both, Sm2Pt6Al15and Sm2Pt6Ga15show the typicalvan Vlecktype behavior along with antiferromagnetic ordering at a Néel temperature ofTN= 4.5(1) K (Al) and ferrimagnetic ordering atTC= 6.5(1) K (Ga). Yb2Pt6Al15exhibits ytterbium in the trivalent oxidation state, while for Yb2Pt6Ga15a divalent state of the Yb atoms was observed.

Preparation and synthesis mechanism of ytterbium monosilicate nano-powders by a cocurrent coprecipitation method

In this study, nano-sized Yb2SiO5 powders were prepared by a cocurrent coprecipitation method. The influence of Si/Yb molar ratio and calcination temperature on the phase composition and structure of Yb2SiO5 were investigated, and the synthesis mechanism of Yb2SiO5 was also discussed. Results indicated that the Si/Yb molar ratio has a significant influence on the phase composition of Yb2SiO5 powders. Under nonstoichiometric conditions, trace of Yb2O3 and Yb2Si2O7 will be formed as impurities in the as-prepared Yb2SiO5 powders. In addition, the elevated calcination temperature can promote the formation of stable X2-Yb2SiO5. During the synthesis process, a -[Si-O-Yb]- network structure was formed in the Yb2SiO5 precursors, which resulted from the in-situ replacement of Si by Yb atoms. The -[Si-O-Yb]- network will transformed to a X1-Yb2SiO5 firstly during the calcination process. With the calcination temperature increased, the metastable X1-Yb2SiO5 can convert to a stable X2-Yb2SiO5 gradually through a reconstructive process. Yb2O3 and Yb2Si2O7 may also be formed during the reconstructive process of X1-Yb2SiO5.