Europium Atoms Research Articles

Dimorphic EuCu5Cd

Two modifications of EuCu5Cd were synthesized from the elements in sealed tantalum ampoules.The high-temperature (HT) modification was obtained from an induction-melted sample that was finally annealed at 873 K, while the low-temperature (LT) phase is formed in a muffle furnace by annealing a pre-melted sample at 673 K. DSC measurements gave a transition temperature of 823±2 K. Both structures were refined on the basis of single-crystal X-ray diffractometer data: R3̄m, a = 511:58(7), c = 3059:6(6) pm, wR2 = 0.0289, 316 F2 values, 22 variables for HTEuCu4 :85(1)Cd1:15(1) and Pnma, a = 2545:6(5), b = 511:60(1), c = 1060:3(2) pm, wR2 = 0.0386, 2044 F2 values, 121 variables for LT-EuCu4:92(1)Cd1:08(1). A small degree of Cu/Cd mixing was observed for three sites. Both structures adopt new types. The europium atoms have high coordination numbers of 18, 19 and 20 in LT- and 18 and 20 in HT- EuCu5Cd. These three types of polyhedra are the basic building units also in the closely related structures of CeCu6, CeCu5Au, CeCu4:38In1:62, and CeNi5Sn, a family of stacking variants. Temperature-dependent magnetic susceptibility measurements of a HT- EuCu5Cd sample showed an experimental magnetic moment of 7.56(1) μB per Eu atom in the paramagnetic regime, compatible with divalent europium. HT- EuCu5Cd orders antiferromagnetically at 17.7(5) K.

Microstructural and photocatatlytic properties of Eu-doped mesporous titanium dioxide nanopaticles by sol–gel method

The europium-doped mesoporous titanium dioxide nanoparticles (Eu-doped TiO2) with the different Eu/Ti rations were prepared using sol–gel method in the presence of tir-block copolymer pluronic P123. The as-prepared catalysts were characterized by low-angle and wide-angle X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), N2 absorption–desorption, ultraviolet visible light spectroscopy (UV–vis) and X-ray photoelectron spectroscopy (XPS), respectively. The XRD analysis indicated that all as-prepared TiO2 samples were mainly anatase phase and mesoporous. The crystallite sizes were in the range 6–11nm, in consistent with the results obtained form TEM images. HRTEM and XPS showed that the europium atoms were doped into the lattice of anatase TiO2. Eu doping can not only increase the stability of mesoporous TiO2, but also make the absorption edge position move toward shorter wavelength. The photodecomposition experiments showed that the photodegradation activity of Eu-doped TiO2 was higher than that of undoped TiO2.

Interaction among different Rydberg series of the europium atom

The spectra of 4f76p1/2(J = 3 or 4)8s, 4f76p1/2(J = 3 or 4)6d and 4f75dnl autoionizing states of the europium atom are investigated using the resonance-ionization spectroscopy method via the same intermediate state, 4f76s(9S4o)8s 8S7/2. The profound interaction among different Rydberg series is observed in this work. The fingerprints of the 4f75d(7D)n′l′ series are identified from the complex structures of autoionization spectra of the 4f76p1/2(J = 3 or 4)8s and 4f76p1/2(J = 3 or 4)6d states. The information of these autoionizing states, such as their level energy, line width, is also provided.

Synthesis, Crystal, and Electronic Structure of the New Ternary Zintl Phase Eu2–xMg2–yGe3 (x = 0.1; y = 0.5)

AbstractThe new ternary phase Eu2–xMg2–yGe3 (x = 0.1, y = 0.5) was obtained by solid‐state synthesis and the structure determined by means of Single Crystal X‐ray Diffraction. The compound crystallizes with the orthorhombic space group Cmcm (no. 63) having structural features of the low‐temperature modification of LaSi. The crystal structure contains two different types of germanium anions: isolated Ge4– and $\rm^{2}_{\infty}$[Ge2–x–y] chains. The cation substructure is partially disordered and is best represented assuming a split position. The chemical bonding is well represented by the Zintl‐Klemm concept. Resistivity measurements reveal that the compound is metallic. DFT band structure calculations were carried out on the ideal stoichiometric compound Eu2Mg2Ge3, showing that this model (x = 0; y = 0) would be also metallic as a consequence of the ecliptic stacking of anions. Susceptibility and specific heat measurements evidence the presence of weak, and probably frustrated, antiferromagnetic interactions between disordered europium atoms.

Exploring the Borders of the Zintl‐Klemm Concept: On the Isopunctual Phases Eu5+xMg18–xGe13(x = 0.1) and Eu8Mg16Ge12

AbstractTwo new ternary compounds Eu5+xMg18–xGe13 (x = 0.1) and Eu8Mg16Ge12 were obtained by solid state synthesis and their crystal structures determined by single crystal X‐ray diffraction. The two compounds crystallize in the hexagonal crystal system (space group P$\bar{6}$2m). Eu5+xMg18–xGe13 (x = 0.1) is a Zintl phase with nine isolated Ge4– ions and a [Ge4]10– star, which is isoelectronic with PF3 but surprisingly almost planar. Eu8Mg16Ge12 contains a [MGe3] (M = Eu, Mg) unit, instead of the [Ge4]10–, and can be described as a salt‐like compound, containing 12 “isolated” Ge4– anions. The structural similarity of these two compounds allows to analyze the chemical bonding of different Zintl anions, which belong to a structural greater isosteric unit. The metallic conductivity of Eu8Mg16Ge12 originates from the ecliptic stacking of the “so‐called isolated” anions along the c direction. In Eu5+xMg18–xGe13 the deviation of the Zintl anion from the planarity causes a semi‐metallic behavior. In both cases, the magnetic response is dominated by the local moments of the europium atoms, which are all found in a 2+ oxidation state. Deviations from the Curie–Weiss law are observed for T < 20 K in the cation‐richer compound and at lower temperatures in the other. The behavior in the low‐temperature range changes with the replacement of the [Ge4]10– star by the MGe3 unit. These studies show that metallic behavior through ecliptic stacking of planar anions can be achieved even with monatomic anions, up to 4.4 Å with germanium at least, and can be destroyed by small deviations from planarity in an extended anion.

Segregation of Cd2 Pairs in CaCu9Cd2 and EuCu9Cd2

AbstractThe copper‐rich intermetallics CaCu9Cd2 and EuCu9Cd2 were synthesized from the elements in sealed tantalum tubes in a high‐frequency furnace. Both compounds were characterized by X‐ray powder and single crystal diffraction: Ce(Mn0.55Ni0.45)11 type, P4/mbm, a = 844.2(1), c = 504.72(8) pm, wR2 = 0.0216, 345 F2 values, 23 variables for CaCu9Cd2 and a = 844.1(2), c = 505.5(1) pm, wR2 = 0.0200, 331 F2 values, 24 variables for EuCu9.14Cd1.86. The europium‐based crystal showed a small mixed Cu/Cd occupancy on the 4g site. The calcium (europium) atoms have the high coordination number 20 (16Cu + 4Cd). These polyhedra are condensed via common Cu4 squares along the c axis. Other striking structural motifs are segregated Cd2 pairs (291 pm in CaCu9Cd2) in copper coordination and slightly distorted Cu2@Cu8Cd4 icosahedra. The latter are connected via common Cd2 pairs along c and form the motif of tetragonal rod packing. EuCu9Cd2 shows paramagnetic behavior above 100 K with an experimental magnetic moment of 7.82(1) μB/Eu atom, indicating purely divalent europium.

Experiment study of ionization limit shift of europium atoms in electric fields

In this paper, we present a new method to determine the first ionization limit of europium atom. Firstly, time delayed field ionization is used to detect highly excited Rydberg states of europium atom. Secondly, reversed static electric field is used to exclude ion signal from photoionization, autoionization and other path. The law of first ionization limit shift of europium atom in electric field is studied. First ionization limit in zero electric field is deduced from data of first ionization limit shift in electric field. This value is well coincident with the reported values deduced by other methods.

Ternary Indides Eu2Pd2In and Eu2Pt2In

AbstractThe indides Eu2Pd2In and Eu2Pt2In were synthesized from the elements in sealed tantalum tubes in an induction furnace. The samples were characterized by powder X‐ray diffraction. The structures were refined on the basis of single‐crystal X‐ray diffractometer data: HT‐Pr2Co2Al type, C2/c, a = 1035.7(2), b = 592.9(1), c = 823.6(2) pm, β = 104.26(1) °, wR2 = 0.026, 1075 F2 values, 25 variables for Eu2Pd2In and a = 1017.2(2), b = 588.7(1), c = 826.5(1) pm, β = 103.76(1) °, wR2 = 0.062, 706 F2 values, 25 variables for Eu2Pt2In. The indium atoms have four platinum (palladium) neighbors in strongly distorted tetrahedral coordination at Pt–In and Pd–In distances ranging from 273 to 275 pm. These InPd4/2 and InPt4/2 units are condensed via common edges to infinite InPd2 and InPt2 chains, which are surrounded by the europium atoms. The chains form the motif of hexagonal rod packing.

Isotope shift and hyperfine structure in even configurations of neutral europium

Results of the measurements of the isotope shifts, as well as the hyperfine structure constants, are presented concerning electronic levels belonging to the even configurations in a europium atom with energies within the range 28 000–43 000 cm−1. The data were obtained with the method of laser-induced fluorescence in a hollow-cathode discharge. On the basis of the measurements of 137 spectral lines, the values of isotope shifts and hyperfine structure constants A and B for 69 levels were determined; in the case of 44 levels, these values were obtained for the first time. Relying on the experimental results, the parameters describing the isotope shifts for individual configurations and the crossed second-order effects were calculated. The results obtained were compared to the ab initio estimations.

Site-selected luminescence of atomic europium in the solid rare gases

Site-selective excitation has been used to simplify complex emission recorded in the visible spectral region for atomic europium isolated in the solid rare gases. In addition to y(8)P resonance fluorescence, excitation of the y(8)P state produces emission from the z(6)P state and the metastable a(10)D state. Very weak emission at 690 nm is tentatively assigned to the J = 9/2 level of the z(10)P state. Eu atoms isolated in the red and blue sites exhibit very different temperature dependence both spectrally and temporally. For the y(8)P state emission the red site atoms exhibit small Stokes shifts and yield radiative lifetimes while the emission from the blue site loses intensity and the temporal profiles shorten dramatically between 10 and 16 K indicating very efficient non-radiative relaxation in this site. An analysis of the Stokes shifts exhibited for the y(8)P state in each site supports the attributions made in a previous publication [O. Byrne and J.G. McCaffrey, J. Chem. Phys. 134, 124501 (2011)] that the smaller blue tetravacancy site has a greater repulsive interaction with the guest. With the exception of the y(8)P state resonance fluorescence, the recorded decay profiles of all the other emissions exhibit multiple components. This behaviour has been attributed to the existence of multiple crystal field levels arising from the splitting of the distinct spin-orbit levels from which emission occurs.

A 121Sb and 151Eu Mössbauer Spectroscopic Investigation of EuCd2X2 (X = P, As, Sb) and YbCd2Sb2

AbstractThe pnictides EuCd2X2 (X = P, As, Sb) and YbCd2Sb2 were synthesized from the elements or a EuCd2 precursor in tantalum tubes. The samples were characterized by powder X‐ray diffraction. The structure of EuCd2As2 was refined on the basis of single‐crystal X‐ray diffractometer data: CaAl2Si2 type, P$\bar{3}$m1, a = 444.99(9), c = 735.0(1) pm, wR2 = 0.0372, 200 F2 values and 10 variables. The two‐dimensional [Cd2X2] networks consist of edge‐sharing CdX4/4 tetrahedra. The networks are separated and charge‐balanced by the europium and ytterbium atoms. Redetermination of the magnetic properties revealed divalent europium and ytterbium. YbCd2Sb2 is diamagnetic. For the europium compounds only one magnetic phase transition is evident, i.e. TC = 11.6 K for EuCd2P2, TN = 9.5 K for EuCd2As2, and TN = 7.4 K for EuCd2Sb2. 151Eu Mössbauer spectra show full magnetic hyperfine field splitting at 4.2 K. A transferred hyperfine field of 7.1 T is evident in the 4.2 K 121Sb spectrum of EuCd2Sb2.

Eu/RG absorption and excitation spectroscopy in the solid rare gases: State dependence of crystal field splitting and Jahn–Teller coupling

Absorption spectroscopy recorded for annealed samples of matrix-isolated atomic europium reveals a pair of thermally stable sites in Ar and Kr while a single site exists in Xe. Plots of the matrix shifts of the visible s → p bands versus host polarizability, allowed the association of the single site in Xe and the blue sites in Ar and Kr. On the basis of the similar ground state bond lengths expected for the Eu-rare gas (RG) diatomics and the known Na-RG molecules, the blue sites are attributed to Eu occupancy in the smaller tetra-vacancy while the red sites are proposed to arise from hexa-vacancy sites. Both sites are of cubic symmetry, consistent with the pronounced Jahn-Teller structure present on the y(8)P ← a(8)S(7/2) transition for these bands in the three hosts studied. Site-selective excitation spectroscopy has been used to reanalyze complex absorption spectra previously published by Jakob et al. [Phys. Lett. A 57, 67 (1976)] for the near-UV f → d transitions. On the basis that a pair of thermally stable sites exist in solid argon, the occurrence of crystal field splitting has been identified to occur for the J ≥ 5/2 level of the (8)P state when isolated in these two sites with cubic symmetry. From a detailed lineshape analysis, the magnitude of the crystal field splittings on the J = 5/2 level in Ar is found to be 105 and 123 cm(-1) for the red and blue sites, respectively.

Study of even-parity highly excited states of Eu I with a three-colour stepwise resonant excitation

Even-parity highly excited states of an europium (Eu) atom have been investigated by employing the three-colour stepwise resonant excitation technique. Seventy-eight even-parity states of the Eu atom have been detected in the energy region between 43 500 and 45 200 cm−1 with two different excitation schemes. With a detailed analysis of the experimental data, this work not only confirms or improves the previous results by determining their level energy, J assignment, but also reports 21 new states of the Eu atom with a unique J assignment. In addition, the information about relative line intensities of these 78 related transitions are also provided for the first time.

Structure and properties of the 5.5 K antiferromagnet EuAu2Ge2

Abstract A well crystallized sample of EuAu2Ge2 was synthesized by arc-melting of the elements. The structure was refined on the basis of single crystal X-ray diffracto meter data: ThCr2Si2 type, I4/mmm, a = 447.3(1), c = 1034.0(4) pm, wR2 = 0.0575, 148 F 2 values and 9 variables. The gold atoms have tetrahedral germanium coordination (261 pm Au—Ge). These AuGe4/4 tetrahedra share four common edges, leading to layers which are connected via Ge—Ge bonds (247 pm). The europium atoms fill cages of coordination number 16 within the [Au2Ge2] δ– polyanion. Temperature dependent susceptibility measurements show a magnetic moment of 7.79(1)μ B/formula unit. Together with the 151 Eu Mössbauer spectroscopic data (isomer shift of –11.43 mm/s at 77 K), the magnetic data point to stable divalent europium. EuAu2Ge2 orders antiferromagnetically at T N1 = 5.5(1) K, followed by a spin-reorientation at T N2 = 3.5 K. A metamagnetic step occurs around 20 kOe in the 4 K magnetization isotherm.

Indium Flux-Growth of Eu2AuGe3: A New Germanide with an AlB2 Superstructure

The germanide Eu(2)AuGe(3) was obtained as large single crystals in high yield from a reaction of the elements in liquid indium. At room temperature Eu(2)AuGe(3) crystallizes with the Ca(2)AgSi(3) type, space group Fmmm, an ordered variant of the AlB(2) type: a = 857.7(4), b = 1485.5(10), c = 900.2(4) pm. The gold and germanium atoms build up slightly distorted graphite-like layers which consist of Ge(6) and Au(2)Ge(4) hexagons, leading to two different hexagonal-prismatic coordination environments for the europium atoms. Magnetic susceptibility data showed Curie-Weiss law behavior above 50 K and antiferromagnetic ordering at 11 K. The experimentally measured magnetic moment indicates divalent europium. The compound exhibits a distinct magnetic anisotropy based on single crystal measurements and at 5 K it shows a metamagnetic transition at ∼10 kOe. Electrical conductivity measurements show metallic behavior. The structural transition at 130 K observed in the single crystal data was very well supported by the conductivity measurements. (151)Eu Mössbauer spectroscopic data show an isomer shift of -11.24 mm/s at 77 K, supporting the divalent character of europium. In the magnetically ordered regime one observes superposition of two signals with hyperfine fields of 26.0 (89%) and 3.5 (11%) T, respectively, indicating differently ordered domains.

Experimental study of bound and autoionizing Rydberg states of the europium atom

An isolated-core-excitation (ICE) scheme and stepwise excitation are employed to study the highly excited states of the europium atom. The bound europium spectrum with odd parity in a region of 42400–43500 cm−1 is measured, from which spectral information on 38 transitions, such as level position and relative intensity, can be deduced. Combined with information about excitation calibration and the error estimation process, the selection rules enable us to determine the possible values of total angular momentum J for the observed states. The autoionization spectra of atomic europium, belonging to the 4f76pnl (l = 0, 2) configurations, are systematically investigated by using the three-step laser resonance ionization spectroscopy (RIS) approach. With the ICE scheme, all the experimental spectra of the autoionizing states have nearly symmetric profiles whose peak positions and widths can be easily obtained. A comparison between our results and those from the relevant literature shows that our work not only confirms many reported states, but also discovers 14 bound states and 16 autoionizing states.

Synthesis, structure, luminescence and magnetic properties of the coordination polymer {[Eu(H2O)5][Mo(CN)8]}∞ containing bridging cyanide ligands

The reaction of [Eu(H2O)6](NO3)3 and [N(C4H9)4]3[Mo(CN)8]·2H2O afforded a new two-dimensional coordination polymer {[Eu(H2O)5[Mo(CN)8]}∞ (1) in which the europium and molybdenum atoms are bound through the bridging CN groups. The luminescence and magnetic properties of complex 1 were studied in a wide temperature range.

Magnetic silicon fullerene

A metal-encapsulating silicon fullerene, Eu@Si(20), has been predicted by density functional theory to be by far the most stable fullerene-like silicon structure. The Eu@Si(20) structure is a dodecahedron with D(2h) symmetry in which the europium atom occupies the center site. The calculated results show that the europium atom has a large magnetic moment of nearly 7.0 Bohr magnetons. In addition, it was found that a stable "pearl necklace" nanowire, constructed by concatenating a series of Eu@Si(20) units, with the central europium atom, retains the high spin moment. The magnetic structure of the nanowire indicates potential applications in the fields of spintronics and high-density magnetic storage.

151Eu Mössbauer Spectroscopic Characterization of EuRu4B4 and the New Boride EuRuB4

Samples of EuRu4B4 and of the new boride EuRuB4 were prepared from europium, RuB, and RuB4 precursor alloys, respectively, in sealed tantalum tubes in an induction furnace. EuRu4B4 crystallizes with the LuRu4B4 structure, a = 748.1(1), c = 1502.3(4) pm. The structure of EuRuB4 was refined on the basis of X-ray diffractometer data: Pbam, a = 599.7(1), b = 1160.7(3), c = 358.06(7) pm, wR2 = 0.0691, 474 F2 values, and 38 variables. The four crystallographically independent boron sites build up layers which consist of almost regular pentagons and heptagons which sandwich the ruthenium and europium atoms, respectively. Within the two-dimensional [B4] networks each boron atom has a slightly distorted trigonal-planar boron coordination with B-B distances in the range 172 - 186 pm. Temperature-dependent 151Eu Mössbauer spectra show stable trivalent europium for EuRu4B4 and EuRuB4

铕原子双色三光子共振电离光谱的研究

铕原子双色三光子共振电离光谱的研究