Barium Atoms Research Articles

Magic wavelengths of the optical clock transition at 877 nm of barium

Magic wavelengths for laser trapping of barium atoms in the optical lattices are investigated while considering the optical clock transition at 877 nm between the 6s21S0 state and 6s5d 1D2 state. Theoretical calculation shows that there are several magic wavelengths with the linearly polarized trapping laser. The trap depths of the optical lattice and the slope of light shift difference with different magic wavelengths are also discussed and analyzed. Some of these magic wavelengths are selected and recommended for the optical lattice trapping laser.

Extreme ultraviolet spectra and analysis of Δn = 0 transitions in highly charged barium

Extreme ultraviolet spectra of highly charged barium atoms were produced with an electron beam ion trap (EBIT) and recorded with a flat-field grazing-incidence spectrometer. The spectra were measured in the wavelength range 4 nm–24 nm with the beam energies varying from 700 eV to 30 000 eV. The line identifications were performed with collisional-radiative modeling of the EBIT plasma that provided good quantitative agreement between simulated and measured spectra. In the energy range 700 eV–1750 eV, fifty three n = 4–n = 4 transitions in Se-like (Ba22+) to Cu-like (Ba27+) ions were identified, with forty seven corresponding to new lines. Almost all lines are due to electric-dipole transitions. For the beam energies of 3945 eV–7530 eV, we identified eight new n = 3–n = 3 transitions in Ba42+ (Si-like), Ba43+ (Al-like), and Ba44+ (Mg-like). At the highest beam energy, 30 000 eV, three new n = 2–n = 2 transitions of Ba51+ (B-like), Ba52+ (Be-like), and Ba53+ (Li-like) were identified. The measured wavelengths are compared with recent ab initio theoretical calculations. An improved ionization energy for Ba26+ (Zn-like), IE = 937.2 ± 0.8 eV, was determined by comparing theoretical values with measurements along the Zn isoelectronic sequence.

New Intermetallic Zinc Compounds with Ordering Variants of the KHg2 and LT-SrZn5 Type

The intermetallic zinc compounds CaAuZn, SrPdZn, SrPtZn, SrAuZn, BaPd1.57 Zn3.43, and BaAu1.41Zn3.59 were synthesized from the elements in sealed niobium ampoules in an induction furnace. The equiatomic compounds crystallize with the orthorhombic TiNiSi-type structure, space group Pnma. Single-crystal X-ray data exhibited small degrees of Au=Zn mixing within the three-dimensional [AuZn] networks and resulted in the compositions CaAu1.02Zn0.98 and SrAu1.03Zn0.97 for two investigated single crystals. BaPd1.57 Zn3.43 and BaAu1.41 Zn3.59 adopt partially ordered versions of the LT-SrZn5 type, space group Pnma. Both structures were refined on the basis of X-ray single-crystal diffractometer data. a=1331.13(6), b=531.45(3), c=682.20(4) pm, wR=0.0245, 1138 F2 values, 39 variables for BaPd1.57Zn3.43 and a=1344.35(2), b=537.47(2), c=691.22(4) pm, wR=0.0441, 931 F2 values, 37 refined variables for BaAu1.41Zn3.59. The transition metal and zinc atoms form a complex three-dimensional network of (T, Zn)4 tetrahedra which are condensed via common corners and T/Zn-T/Zn bonds. Large cavities within these networks are filled by the barium atoms which have coordination number 19, i. e. Ba@(T, Zn)17Ba2.

Ba@Sn10 and Ru@Sn7/Rh@Sn7 polyhedra as basic building units in the stannides BaT 5–x Sn9 (T = Ru, Rh)

The tin-rich stannides BaRh5–x Sn9 and BaRu5–x Sn9 were synthesized by direct reactions of the elements in sealed niobium or tantalum tubes in muffle furnaces. Their structures were refined from X-ray single-crystal diffractometer data: BaCo4.7Ge9 type, Pnma, Z = 4, a = 1,553.44(8) pm, b = 438.38(2) pm, c = 1,861.5(1) pm, wR = 0.0558, 2,787 F 2 values for BaRh4.43Sn9, a = 1,554.09(6) pm, b = 438.44(1) pm, c = 1,873.44(5) pm, wR = 0.0589, 2,184 F 2 values for BaRh4.68Sn9, and a = 1,560.7(2) pm, b = 440.24(4) pm, c = 1,869.0(3) pm, wR = 0.0674, 2,197 F 2 values for BaRu4.57Sn9 with 93 variables per refinement. The Rh5 and Ru5 sites show small defects. The shortest interatomic distances occur for Ru–Sn and Rh–Sn, leading to Ru@Sn7 and Rh@Sn7 building units that derive from an octahedron by replacing one apex by a pair of tin atoms. These units condense by common triangular and rectangular faces forming a three-dimensional network in which the barium atoms fill slightly distorted pentagonal prismatic voids.

Production of Ba Metastable State via Superradiance

We describe in this paper a fast and efficient method of producing a high density of barium (Ba) atoms in the 1D2 metastable state, which is a candidate initial state for a new class of cooperative...

Atomic resolution imaging and spectroscopy of barium atoms and functional groups on graphene oxide.

We present an atomic resolution transmission electron microscopy (TEM) and scanning TEM (STEM) study of the local structure and composition of graphene oxide modified with Ba(2+). In our experiments, which are carried out at 80kV, the acquisition of contamination-free high-resolution STEM images is only possible while heating the sample above 400°C using a highly stable heating holder. Ba atoms are identified spectroscopically in electron energy-loss spectrum images taken at 800°C and are associated with bright contrast in high-angle annular dark-field STEM images. The spectrum images also show that Ca and O occur together and that Ba is not associated with a significant concentration of O. The electron dose used for spectrum imaging results in beam damage to the specimen, even at elevated temperature. It is also possible to identify Ba atoms in high-resolution TEM images acquired using shorter exposure times at room temperature, thereby allowing the structure of graphene oxide to be studied using complementary TEM and STEM techniques over a wide range of temperatures.

Electrical properties of Ba3C60 collapsed under high-pressure and high-temperature conditions

The barium doped fulleride Ba3C60 was treated under high-pressure and high-temperature conditions of 5–15GPa and temperatures up to 1150°C. Amorphous solids stable in air were obtained. The high micro Vickers hardness and the Raman spectra of the solids suggest that the C60 molecules are collapsed to form amorphous three-dimensional (3D) polymer encapsulating Ba atoms. The solids show a semi-metallic conductivity with a positive Hall coefficient. It is likely that barium atoms are trapped in the carbon network, replacing carbon atoms as clusters, and act as dopants for holes. The low electrical mobility of the solid is attributable to the lack of 3D periodicity of the polymer.

Synthesis, crystal structure and electronic properties of the new iron selenide Ba9Fe4Se16

The new ternary selenide Ba9Fe4Se16 has been synthesized from the reaction of appropriate amounts of elements at high temperature in a silica sealed tube. The compound crystallizes in the tetragonal space group I41/a with a=10.0068(3)Å and c=35.6415(9)Å, Z=4. It is an isostructural compound to the sulfide α-Ba9Fe4S15, which is a high temperature polymorph of β-Ba9Fe4Se15 that belongs to the indefinitely adaptive phases series Ba3Fe1+xS5, 0≤x≤1. X-ray powder diffraction and TEM analyses of the synthesized compound were used to determine the phase composition and the structure. The crystal structure can be viewed as overlapping sections along the c axis. Those sections are formed by the coordination polyhedra around barium atoms which can be described as trigonal prisms and bidisphenoids. Within the sections formed by barium polyhedra, isolated pairs of edge sharing FeSe4 tetrahedra are found. Magnetic measurements performed on Ba9Fe4Se16 indicate an antiferromagnetic behavior with Néel temperature of ~13K. Possible influence of air exposure on the magnetic properties is also discussed here. The electric measurements show an insulating behavior below 160K and the dielectric permittivity and loss tangent at the lowest frequency measured reveal a change of slope very close to TN. However no magneto dielectric effect was evidenced for magnetic fields of up to 3T. Activation energy, EA=0.18eV, was extracted from the AC conductivity plot in the temperature range of 160–300K.

Studies on Nano Crystalline Ceramic Superconductor LaZrYBaCa<sub>2</sub>Cu<sub>3</sub>O<sub>11</sub> at Three Different Temperatures

The high temperature superconductors are ceramic materials with layers of Copper-oxide spaced by layers containing Barium and other atoms. The Yttrium compound is somewhat unique in that it has a regular crystal structure while the Lanthanum version is classified as a solid solution. The Yttrium compound is often called the 1-2-3 superconductor because of the ratios of its constituents. Lanthanum Zirconium Yttrium Barium Calcium Copper Oxide (LaZrYBaCaCuO) was prepared by the usual solid state reaction method. In order to show the viability of the proposed method, super-conducting powder was prepared in special furnace. The sample was analyzed by X-ray Diffraction (XRD), Particle size determination, SEM and EDX. The comparison of XRD results with JCPDS files confirmed the orthorhombic structure of the sample with a ≠ b ≠ c and α = β = γ = 90°. Scanning Electron Microscopy (SEM) studies revealed that its particle size is in the nanometer range. It also confirmed the calculated value of particle size from Debye Scherrer’s formula. EDX spectrum shows the elements of the sample. X-ray instrumental peak broadening analysis was used to evaluate the size and lattice strain by the Williamson-Hall Plot method.

Superconductivity in Ba1−xKxTi2Sb2O (0 ≤ x ≤ 1) controlled by the layer charge

The solid solution of antimonide-oxides Ba1−xKxTi2Sb2O (0 ≤ x ≤ 1) has been synthesized by solid-state reactions and characterized by X-ray powder diffraction (CeCr2Si2C-type structure; P4/mmm, Z = 1). The crystal structure consists of Ti2Sb2O-layers that are stacked with layers of barium atoms along the c-axis. BaTi2Sb2O is a known superconductor with a critical temperature (Tc) of 1.2 K. Substitution of barium through potassium raises Tc up to 6.1 K at 12% potassium, while no superconductivity emerges with concentrations higher than 20%. Anomalies in electrical transport and magnetic susceptibility indicate charge density wave (CDW) instabilities. The CDW transition temperatures (Ta) decrease from 50 K in the parent compound to 28 K at 10% potassium substitution. No CDW transition was detected at higher concentrations, and no evidence for a reduction of the lattice symmetry below Ta was found. The lattice parameters vary linearly while the unit cell volume increases with higher potassium concentrations. The phase diagrams Tc(x) and Ta(x) of Ba1−xKxTi2Sb2O are remarkably similar to the known series Ba1−xNaxTi2Sb2O (0 ≤ x ≤ 0.33) in spite of the reverse volume effect. From this we conclude that the charge and not the volume determines the phase diagrams of these superconducting antimonide-oxides.

Local Structure of Ba1–xSrxTiO3 and BaTi1–yZryO3 Nanocrystals Probed by X-ray Absorption and X-ray Total Scattering

The effect of isovalent chemical substitution on the magnitude and coherence length of local ferroelectric distortions present in sub-20 nm Ba(1-x)Sr(x)TiO3 (x = 0.0, 0.30, 0.50, 1.0) and BaTi(1-y)Zr(y)O3 (y = 0.0, 0.15, 0.50, 1.0) nanocrystals synthesized at room temperature is investigated using X-ray absorption near edge structure (XANES) and pair distribution function analysis of X-ray total scattering data (PDF). Although the average crystal structure of the nanocrystals is adequately described by a centrosymmetric, cubic Pm3m space group, local ferroelectric distortions due to the displacement of the titanium atom from the center of the perovskite lattice are observed for all compositions, except BaZrO3. The symmetry of the ferroelectric distortions is adequately described by a tetragonal P4mm space group. The magnitude of the local displacements of the titanium atom in BaTiO3 nanocrystals is comparable to that observed in single crystals and bulk ceramics, but the coherence length of their ferroelectric coupling is much shorter (≤20 Å). Substitution of Sr(2+) for Ba(2+) and of Zr(4+) for Ti(4+) induces a tetragonal-to-cubic transition of the room temperature local crystal structure, analogous to that observed for single crystals and bulk ceramics at similar compositions. This transition is driven by a reduction of the magnitude of the local displacements of the titanium atom and/or of the coherence length of their ferroelectric coupling. Replacing 50% of Ba(2+) with Sr(2+) slightly reduces the magnitude of the titanium displacement, but the coherence length is not affected. In contrast, replacing 15% of the ferroelectrically active Ti(4+) with Zr(4+) leads to a significant reduction of the coherence length. Deviations from the ideal solid solution behavior are observed in BaTi(1-y)Zr(y)O3 nanocrystals and are attributed to an inhomogeneous distribution of the barium atoms in the nanocrystal. Composition-structure relationships derived for Ba(1-x)Sr(x)TiO3 and BaTi(1-y)Zr(y)O3 nanocrystals demonstrate that the evolution of the room temperature local crystal structure with chemical composition parallels that of single crystals and bulk ceramics, and that chemical control over ferroelectric distortions is possible in the sub-20 nm size range. In addition, the potential of PDF analysis of total scattering data to probe compositional fluctuations in nanocrystals is demonstrated.

Crystal structure of barium germanide, BaGe1.51

Abstract BaGe1.51, hexagonal, P6/mmm (no. 191), a = 4.458(2) Å, c = 4.867(3) Å, V = 83.78(6) Å3, Z = 1, Rgt(F) = 0.0132, wRref(F2) = 0.0292, T = 293 K.

Thermal stability of YBa2Cu3O7−δ films deposited on Ni-W textured substrates by laser ablation

The degradation processes of YBa2Cu3O6.77(3) films 600 nm thick deposited on substrates from a textured (100) foil of the Ni-W alloy with the YSZ (Y2O3 + ZrO2) (100 nm) and CeO2 (50 nm) buffer layers at 200°C in air have been investigated. It has been shown that the degradation proceeds in the same manner as in the bulk ceramic materials with the same oxygen content, namely, initially the single-phase material with the orthorhombic structure laminates into the fractions depleted (the main fraction) and enriched with oxygen. After holding for more than 20 h, the oxygen-depleted fraction is first subjected to the structural phase transformation with the transition of the orthorhombic structure into the cubic one, which is associated with the redistribution of barium and yttrium atoms over their sites in the presence of water vapors.

Probability of the two-electron mechanism of the formation of doubly charged barium ions as a function of laser radiation intensity

The formation of singly and doubly charged ions upon nonlinear ionization of barium atoms is studied as a function of the frequency and intensity of a 8800-8920-cm−1 IR color center laser. Barium atoms are ionized via the four-photon resonance with the strongly perturbed bound 6p21D2 state. Doubly charged barium ions are produced by a two-electron mechanism. It is found that the probability of the formation of doubly charged ions under these conditions linearly depends on the laser radiation intensity.

A1 EFFECTS OF AQUATIC THERAPY ON PAIN OF NEWBORNS UNDER MECHANICAL VENTILATION IN A NEONATAL INTENSIVE CARE UNIT

The new barium β-diketonate complexes with 18-crown-6 [Ba(adtfa)2(18-crown-6)] (1) and [Ba(adtfa)2(18-crown-6)](CDCl3)2 (2) (adtfa = 1,1,1-trifluoro-4-(1-adamantyl)-2,4-butanedionato, 18-crown-6 = 1,4,7,10,13,16-hexaoxacycloocta-decane) were synthesized and characterized by elemental analysis, IR-, 1H NMR-spectroscopy and X-ray diffraction analysis. The mutual arrangement of the β-diketonate ligands relative to the barium atoms in 1 and 2 was found to be different. The nature of chemical interactions and charges distribution in 1 and 2 was investigated using an experimental-theoretical approach based on crystal (asymmetric unit–cell aspherical scattering factor) and molecular (whole–molecule aspherical scattering factor) invarioms within the framework of Bader theory. It was shown that the less favorable conformation of complex 2 is stabilized in the crystal by the higher energy of intermolecular interactions as compared to 1. The energy of intermolecular interactions (94.3 kJ/mol) in 1 was estimated by electron density topological analysis and agrees well with the experimentally obtained sublimation enthalpy (83.2 ± 1.1 kJ/mol).

Structure and thermodynamic properties of positive and negative cluster ions in saturated vapour over barium dichloride

Geometrical structure, vibration spectra, and enthalpies of dissociation have been investigated for the ions BaCl3−, Ba2Cl3+, Ba3Cl5+, and Ba4Cl7+ which were detected earlier in the saturated vapour over BaCl2. Quantum chemical methods of density functional theory, the second and the fourth order Møller–Plesset perturbation theory have been applied. The effective core potential with cc-pVTZ basis set for barium atom and two full-electron basis sets including the diffuse and polarised basis functions for chlorine atom were used. The effect of the basis set size and the computation method on the results was analysed. According to the results, all the ions possess the compact shaped structure. The equilibrium geometrical structures were found as follows: the planar D3h for BaCl3−, triple bridged bipyramidal D3h for Ba2Cl3+, hexabridged D3h for Ba3Cl5+, and septuple bridged C2v for Ba4Cl7+. For positive ions, the different isomeric structures were considered, but no isomers for these ions have been found. The geometrical parameters and vibration frequencies were utilised for computing of thermodynamic functions of the ions, and then the thermodynamic functions were used for the treatment of the experimental mass spectrometric data. The enthalpies of formation ΔfH°(0 K) of the ions were determined (in kJ/mol): −994 ± 6 (BaCl3−), −481 ± 10 (Ba2Cl3+), −1276 ± 14 (Ba3Cl5+), −2048 ± 35 (Ba4Cl7+).

SrCo2Sn8 and BaCo2Sn8: Tin-rich Stannides with Distorted SnSn6 Octahedra within Three-dimensional [Co2Sn8] Networks

Abstract The tin-rich stannides SrCo2Sn8 and BaCo2Sn8 were synthesized from the elements in sealed tantalum tubes. They crystallize with a new structure type, space group Cccm with a=1006.0(3), b=1514.4(6), c=1385.0(6) pm for SrCo2Sn8 and a=1032.8(2), b=1516.8(3), c=1405.1(3) pm for BaCo2Sn8. The structure of the barium compound was refined on the basis of single-crystal Xray diffractometer data: wR2=0.0450, 1715 F2 values, 57 variables. The cobalt atoms have seven nearest tin neighbors with Co-Sn distances ranging from 257 to 273 pm. These CoSn7 units are condensed via common rectangular faces to [Co2Sn10] double units which build up a covalently bonded three-dimensional network through Sn-Co-Sn bridges. Larger voids left by this network are filled by the barium and the Sn2 atoms. The latter have distorted octahedral tin coordination with Sn2- Sn distances of 311 - 315 pm. The barium atoms have 13 nearest tin neighbors (352 - 399 pm Ba-Sn). Temperature-dependent magnetic susceptibility data of BaCo2Sn8 show Pauli paramagnetism.

Stark spectrum of barium in highly excited Rydberg states

We present observations of Stark spectra of barium in highly excited Rydberg states in the energy region around n = 35. The one-photon excitation concerns the π transition. The observed Stark spectra at electric fields ranging from 0 to 60 V·cm−1 are well explained by the diagonalization of the Hamiltonian incorporating the core effects. From the Stark maps, the anti-crossings between energy levels are identified experimentally and theoretically. The time of flight spectra at the specified Stark states are recorded, where the deceleration and acceleration of barium atoms are observed. This is very consistent with the prediction derived from the Stark maps from the point of view of energy conservation.

An effective quantum defect theory for the diamagnetic spectrum of a barium Rydberg atom

A theoretical calculation is carried out to investigate the spectrum of a barium Rydberg atom in an external magnetic field. Using an effective approach incorporating quantum defect into the centrifugal term in the Hamiltonian, we reexamine the reported spectrum of the barium Rydberg atom in a magnetic field of 2.89 T [J. Phys. B 28 L537 (1995)]. Our calculation employs B-spline basis expansion and complex coordinate rotation techniques. For single photon absorption from the ground 6s2 to 6snp Rydberg states, the spectrum is not influenced by quantum defects of channels ns and nd. The calculation is in agreement with the experimental observations until the energy reaches E = −60 cm−1. Beyond this energy, closer to the threshold, the calculated and experimental results do not agree with each other. Possible reasons for their discrepancies are discussed. Our study affirms an energy range where the diamagnetic spectrum of the barium atom can be explained thoroughly using a hydrogen model potential.

Multiphoton laser ionization for energy conversion in barium vapor

We have studied the ion detection of barium atoms in special heated ovens with a tungsten rod in the middle of the stainless steel tube. The tungsten rod was heated indirectly by the oven body heaters. A bias voltage between the cell body and the tungsten rod of 9V was used to collect electrons, after the barium ions had been created. However, we could collect the electrons even without the bias voltage, although with ten times less efficiency. We studied the conditions for the successful bias-less thermionic signal detection using excimer/dye laser two-photon excitation of Rydberg states below and above the first ionization limit (two-photon wavelength at 475.79nm). We employed a hot-pipe oven and heat-pipe oven (with inserted mesh) in order to generate different barium vapor distributions inside the oven. The thermionic signal increased by a factor of two under heat-pipe oven conditions.