Ba Atoms Research Articles

Self‐Assembled Composite Cathodes with TEC Gradient for Proton‐Conducting Solid Oxide Fuel Cells

AbstractOne of the key challenges for high‐performance proton‐conducting solid oxide fuel cells (H‐SOFCs) is the mismatch in thermal expansion coefficients (TEC) between the cathode and electrolyte. While incorporating negative thermal expansion (NTE) materials can mitigate this issue, mechanical mixing often weakens cathode strength. To address this, a TEC gradient cathode is proposed and successfully implemented by co‐sintering PrBa(Co0.7Fe0.3)2O5‐δ(PBCF) with Y2W3O12 (YWO) in this work. In this work, Ba atoms at the A‐site of PBCF migrated from the lattice, generating A‐site defects. The resulting BaWO4 and Y10W8O21 phases, which have low TEC, are uniformly distributed between PBCF and YWO, forming a TEC gradient composite cathode. In addition, the transition phase captures the A‐site element Ba in the electrolyte layer, optimizing the electrolyte‐cathode interface. The composite cathode exhibits a reduced TEC, closely matching that of the electrolyte, significantly enhancing interface bonding, thereby providing a lower ohmic resistance of 0.051 Ω cm2 and a higher power density of 1.88 W cm−2 at 700 °C. Remarkably, thermal cycling tests conducted under temperature switching conditions demonstrate the composite cathode's long‐term thermal and chemical stability.

Magnetocrystalline anisotropy energy of AYbO3 (A= Sr, Ba and Ca) perovskite oxides

First-principles calculations and Monte Carlo simulations were employed to explore the effect of magnetic anisotropy on magnetocaloric properties and the magnetocrystalline anisotropy energy (MAE) of AYbO3 (A = Sr, Ba and Ca) perovskite oxides. The equilibrium lattice constant a0 is calculated AYbO3 (A = Sr, Ba and Ca). The elastic constants and related mechanical quantities such as bulk modulus B, Zener anisotropy factor A and Cauchy pressure Cp were calculated. CaYbO3 and SrYbO3 exhibit the half-metallic characteristic. While BaYbO3 exhibits semiconductor character. Sr, Ba and Ca atoms located in the A site affected the values of magnetocrystalline anisotropy energy (MAE) so changing the sign of the magnetic anisotropy constant in SrYbO3. The magnetic anisotropy shows that the easy axis is along the axis [100] for SrYbO3, CaYbO3 and BaYbO3 respectively. The critical temperature around Tc = 65 K using the MCS method. The isothermal magnetic entropy change was calculated for BaYbO3 under different magnetic fields and magnetic anisotropy. The highest isothermal entropy change obtained at H = 5T and D = 0 is 5.51 J/kg.K. While it’s equal to 8.10 J/kg.T at H = 5T and D =5.

Optical and electronic properties of RENiO3 doped with alkali earth metals (Be, Mg, Ca, Sr and Ba): Combining first principles calculations and machine learning

The perovskite rare earth nickelate (RENiO3) has attracted significant attention owing to its peculiar physical properties and promising potential for diverse applications. It is reported that introducing H or Li might change the electronic and optical properties of RENiO3. However, little is known about multi-electrons doping in RENiO3. In this study, the bandgaps, optical and electronic properties were investigated in RENiO3 with alkaline earth metal (AEM) elements (Be, Mg, Ca, Sr and Ba) doping. For the atomic configurations of doped RENiO3, the interstitial sites of RENiO3 are more likely to be occupied by Be, Mg and Ca atoms, whereas Sr and Ba atoms tend to replace RE atoms in RENiO3. The band gap of RENiO3 decreases after AEM doping. Moreover, the machine learning results found that the formation energy of the AEM, the relative atomic mass of the AEM, and the doping position significantly influence the band gap. Furthermore, the infrared light blocking capability, the visible light transmission, and the electronic conductivity are enhanced in AEM doped RENiO3. This study may contribute to the experimental modulation of the optical and electronic properties of RENiO3 through AEM doping.

Global Optimization of Cation Ordering in Perovskites by Recommendation-Based Basin-Hopping.

Cation ordering in multication perovskites is related to many important material properties and performances, but computational determination of the cation ordering remains a major challenge. Here, we propose a new computational approach by introducing a machine learning recommender system into the basin-hopping framework (RBH) for optimizing cation ordering. Taking the electrocatalyst Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF5582) as a showcase example, we found that the efficiency of RBH in identifying low-energy configurations outperforms the methods of cluster expansion and conventional basin-hopping. The RBH results revealed that the BSCF5582 catalyst tended to have a layered ordering of A-site cations and disordered B-site cations both in bulk and on the surfaces. Further, on the A-site-terminated surface, we found the segregation of large Ba atoms. Similarly, on the A-site- terminated surface of the recently developed Cs0.2Sr0.8Co0.4Fe0.6O3 (CSCF2846) catalyst, layered ordering at the A-site and surface enrichment of large Cs atoms were also found. The layered ordering was robust against thermal effects, as found from molecular dynamics simulations at 800 K. This work provides a new approach for thermodynamic global optimization of chemical ordering in multicomponent materials.

Ring Structures of Metal Atom Doped C9, C11, and C13 Clusters from Ab Initio Calculations-The Finding of a Gd@C13 Magnetic Superatom Ring.

Pure C9 clusters have a linear chain structure. However, here, we report using ab initio calculations the transformation of a chain into a cyclic ring structure with the capping of Ca, Sr, and Ba atoms. Further calculations on neutral and charged clusters doped with Sc, Y, and La atoms show stabilization of a cation C9 isoelectronic cyclic ring capped with the metal (M) atom, but anion clusters doped with these trivalent atoms form a C10 like MC9 ring, which deforms to a necklace structure. Both the ring structures correspond to electronic shell closing with 20 delocalized valence electrons in a disk jellium model and have a large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap. Calculations of IR and Raman spectra show no imaginary frequency, suggesting that the structures are stable. Addition of two C atoms to the ring structure of LaC9 leads to a capped ring structure of the cation LaC11 and an open ring structure of the LaC11 anion. Further addition of two C atoms leads to a La@C13 cation as well as Ca@C13 and Sr@C13 neutral wheel-shaped rings with endohedral doping of the M atom. These novel ring structures have a large HOMO-LUMO gap of more than 4 eV and are magic with electronic shell closing corresponding to 28 delocalized valence electrons in a disk jellium model. There is π aromaticity in this ring satisfying 4n+2 (n = 3) Hückel's rule with 14 valence electrons. Interestingly, when the dopant is a Gd atom, there is a formation of a magnetic superatom ring Gd@C13 + with 7 μB magnetic moments due to seven 4f up-spin states of Gd being fully occupied. Bonding in these novel ring structures is discussed.

Excitation Dynamics of the 5p^6 Auger Spectra in Ba + e^– Collisions

The ionization of the 5p6 subshell in Ba atoms has been studied in an electron-impact energy range 23–105 eV by measuring the Auger spectra arising from the decay of the 5p5nln′l′ states. The energy dependences of the ionization cross-section have been obtained for nine states in the 5p55d2, 5p55d6s and 5p56s2 configurations. The analysis of the behavior of the cross-sections made it possible to determine the role of direct and indirect ionization processes involved in the 5p6 ionization of the Ba atom.

Precision Atomistic Structures of Actinium-/Radium-/Barium-Doped Lanthanide Nanoconstructs for Radiotherapeutic Applications.

Lanthanide vanadate (LnVO4) nanoconstructs have generated considerable interest in radiotherapeutic applications as a medium for nanoscale-targeted drug delivery. For cancer treatment, LnVO4 nanoconstructs have shown promise in encapsulating and retaining radionuclides that emit alpha-particles. In this work, we examined the structure formation of LnVO4 nanoconstructs doped with actinium (Ac) and radium (Ra), both experimentally and using large-scale atomistic molecular dynamics simulations. LnVO4 nanoconstructs were synthesized via a precipitation method in aqueous media. The reaction conditions and elemental compositions were varied to control the structure, fluorescence properties, and size distribution of the LnVO4 nanoconstructs. LnVO4 nanoconstructs were characterized by X-ray diffraction, Raman spectroscopy, and fluorescence spectroscopy. Molecular dynamics simulations were performed to obtain a fundamental understanding of the structure-property relationship between radionuclides and LnVO4 nanoconstructs at the atomic length scale. Molecular dynamics simulations with well-established force field (FF) parameters show that Ra atoms tend to distribute across the nanoconstructs' surface in a broader coordination shell, while the Ac atoms are arranged inside a smaller coordination shell within the nanocluster. The Ba atoms prefer to self-assemble around the surface. These theoretical/simulation predictions of the atomistic structures and an understanding of the relationship between radionuclides and LnVO4 nanoconstructs at the atomic scale are important because they provide design principles for the future development of nanoconstructs for targeted radionuclide delivery.

BaCu, a Two-Dimensional Electride with Cu Anions.

The electron-rich characteristic and low work function endow electrides with excellent performance in (opto)electronics and catalytic applications; these two features are closely related to the structural topology, constituents, and valence electron concentration of electrides. However, the synthesized electrides, especially two-dimensional (2D) electrides, are limited to specific structural prototypes and anionic p-block elements. Here we synthesize and identify a distinct 2D electride of BaCu with delocalized anionic electrons confined to the interlayer spaces of the BaCu framework. The bonding between Cu and Ba atoms exhibits ionic characteristics, and the adjacent Cu anions form a planar honeycomb structure with metallic Cu-Cu bonding. The negatively charged Cu ions are revealed by the theoretical calculations and experimental X-ray absorption near-edge structure. Physical property measurements reveal that BaCu electride has a high electronic conductivity (ρ = 3.20 μΩ cm) and a low work function (2.5 eV), attributed to the metallic Cu-Cu bonding and delocalized anionic electrons. In contrast to typical ionic 2D electrides with p-block anions, density functional theory calculations find that the orbital hybridization between the delocalized anionic electrons and BaCu framework leads to unique isotropic physical properties, such as mechanical properties, and work function. The freestanding BaCu monolayer with half-metal conductivity exhibits low exfoliation energy (0.84 J/m2) and high mechanical/thermal stability, suggesting the potential to achieve low-dimensional BaCu from the bulk. Our results expand the space for the structure and attributes of 2D electrides, facilitating the discovery and potential application of novel 2D electrides with transition metal anions.

Structural Interaction between BaO and Al2O3 in Aluminosilicate Slags

The effect of BaO and Al2O3 on the viscosity of SiO2–CaO–MgO–Al2O3–BaO slag from 1673 to 1873 K is studied by the rotating cylinder method. The structure of slag is examined by Raman spectroscopy and molecular dynamics simulation. In this study of viscosity, Al2O3 shows amphoteric oxide characteristics and BaO shows characteristics different from the basic oxide. The viscosity increases as the BaO increases from 2 to 4 wt% in the slag with CaO/SiO2 = 1.07. However, the viscosity decreases when the BaO content increases from 6 to 8 wt%. From molecular dynamics simulations and Raman analysis, the increase in BaO content leads to a greater aggregation of Al around Ba atoms and increases the number of Al–O bonds. This indicates that higher BaO content promotes the polymerization of the [AlO4] tetrahedral structure. Furthermore, a good quantitative relationship between viscosity and the ratio of Q3/Q2 of the Raman spectrum of the slag is observed.

Towards highly-selective H2O2 photosynthesis: In-plane highly ordered carbon nitride nanorods with Ba atoms implantation

Graphitic carbon nitride (g-C3N4) shows great potential in photocatalytic H2O2 production. However, challenges arise from its low in-plane crystallinity and selectivity in two-electron oxygen reduction reaction (2e−-ORR), greatly limiting its H2O2 photosynthesis efficiency. Herein, we develop an ingenious strategy to simultaneously increase the in-plane crystallinity and induce the highly-selective 2e−-ORR by rationally designing barium (Ba) atom-implanted in-plane highly ordered g-C3N4 nanorods. The approach involves controllable synthesis of in-plane high crystallinity g-C3N4 nanorods with Ba implantation (BI-CN) using a BaCl2-mediated in-plane polymerization strategy. The unique Ba-N interaction induces the oriented polymerization of 3-s-triazine units to form well-arranged in-plane structures. Experimental and theoretical calculations clarify that the implanted Ba atoms function as positive charge centers, resulting in a Pauling-type O2 adsorption configuration. This minimizes O–O bond breaking energy, thus suppressing the four-electron oxygen reduction reaction (4e−-ORR) and facilitating a highly-selective 2e−-ORR pathway for efficient photocatalytic H2O2 production. Consequently, the optimized BI-CN3 photocatalyst exhibits an outstanding H2O2 production rate of as high as 353 μmol L−1 h−1, surpassing the pristine g-C3N4 by 6.1 times. This study concurrently optimizes the in-plane crystallinity and O2 adsorption sites of g-C3N4 photocatalysts for highly-selective H2O2 production, providing innovative insights for designing efficient photocatalysts with diverse applications.

Physical adsorption of the Ba atom on Arn surfaces: spectroscopic and geometric properties

Barium atoms cause several environmental and ecological dangers. Numerous techniques are employed to remove the Ba atom such as physisorption and solvation methods. In this work, we are interested in investigating and exploring the Ba atom’s physical adsorption on argon surfaces. We have tested several optimizations and we have found that the first range of Ar atoms (n = 1–12) presents more than 90% of the energy interaction between Ba and the adsorbent surface. Therefore, we started by computing and analyzing the potential energy surfaces (PESs) of BaArn molecules. Large basis sets and full Configurations Interaction (full-CI) with the pseudo-potential approach were used to perform the PES, the spectroscopic parameters, vibrational energy levels, and electric dipole moment (EDM) for the selected states. The structural properties and relative stability of Ba (6s2 1S)Arn (n = 1–13, 30, 44, and 54) clusters are determined using Monte Carlo simulation based on the Potential Model method (MC-PM). Several clusters (n > 4) were demonstrated to be stable using MC simulations, and the Ba atom is always present on the surface of the remaining Arn cluster. We have found a good concordance between our results and the available theoretical and experimental data. The spectroscopic information of these complexes can be used by experimental researchers for the investigation of optical mechanisms collision, especially the deformation of the Ba spectrum by collision with the argon surface.

Ba-leaching-initiated structural destabilization of perovskite Ruthenates during the oxygen evolution reaction

The destabilization of a lattice structure during the oxygen evolution reaction (OER) is one of the most essential aspects for designing and realizing highly efficient electrocatalysts. However, the underlying mechanism of structural evolution or degradation at the microscopic scale on the electrocatalyst surface during the OER has not been elucidated because of the sluggish yet dynamic character of the reaction. To address this issue, the direct observation of the unstable electrocatalytic activity is necessary. In this study, we demonstrate that the structural destabilization of epitaxial cubic perovskite BaRuO3 thin films during the OER originates from Ba leaching, Ru dissolution, and oxygen vacancy. A thin film geometry is adopted to selectively visualize the structural decomposition at the well-defined sample surface. The cubic BaRuO3 thin film initially exhibits high OER activity, which drastically decreases even during the first cyclic voltammetry cycle and is completely lost after the first cycle. The OER activity loss is closely related to the generation of structural defects on the surface, indicating the absence of the Ba and Ru atoms. This study proposes the mechanism underlying the OER activity that can be extended to elucidate the structural destabilization in various Ru- and Ir-based oxide catalysts.

Single crystal synthesis and physical property of Ba8Cu1·0Ni2.5Ga10Si33.5 clathrate

This study reports the synthesis of type-I Ba8CuNi2.5Ga10Si33.5 clathrate as a single crystal by the flux method and physical properties investigations such as structural, chemical, magnetic, and thermal properties. Structural refinements indicate Ba atoms are situated at 2a and 6d positions with mixed occupancy across framework sites. Raman spectroscopy assessed host-guest interactions, while the compound's morphology and composition were investigated by the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) analyses. Magnetic properties revealed ferromagnetic interactions characterized by a positive Weiss constant and weak ferromagnetic hysteresis. The compound's metallic nature is evidenced by increased resistivity with temperature. The Sommerfeld coefficient, estimated at 12.59 mJ mol−1 K−2 from heat capacity data, alongside a pronounced peak around 15 K in the Cp/T3 vs T plot, suggests an Einstein contribution in heat capacity.

A DFT study of (La2O3)n clusters and effect of Ba, Y and Hf doping for their optoelectronic applications

( La 2 O 3 ) n (n=1-5) clusters have been computationally studied using DFT and TDDFT with B3LYP functional under hybrid GGA approximation and LANL2DZ basis set. The doping effect of various elements like Ba, Y and Hf on the structural, electronic and non-linear optical (NLO) properties of ( La 2 O 3 ) n clusters has been studied for finding their optoelectronic applications. Different optimised geometries of ( La 2 O 3 ) n and Ba, Y and Hf doped ( La 2 O 3 ) n clusters have been obtained. HOMO-LUMO gap ( Δ E ) and chemical hardness (τ) of ( La 2 O 3 ) n clusters decreases significantly with doping of Ba, Y and Hf atoms making these clusters very reactive. Refractive index and the absorption in UV–VIS region of electromagnetic spectra of Ba, Y and Hf doped ( La 2 O 3 ) n clusters increases as compared to ( La 2 O 3 ) n clusters making these clusters suitable to be used as additives in the manufacturing of various types of glasses. Also, dielectric constant (ϵ) of Ba, Y and Hf doped ( La 2 O 3 ) n clusters increases finding their applications to be used in the oxide layer of MOSFETs.

Direct Imaging of Atomic Rattling Motion in a Clathrate Compound

Controlling nanoscale heat generation, dissipation, and transport is crucial for miniaturizing electronic devices and for designing highly efficient thermoelectric materials. However, it has been challenging to directly measure thermal properties at individual atom level. Herein, direct atomic‐resolution column‐by‐column imaging of the rattling motion of Ba atoms in a clathrate compound Ba8Ga16Ge30 using atomic‐resolution scanning transmission electron microscopy with a segmented detector is shown. The directional anisotropy of the rattling motion is clearly visualized in real space and its amplitude and anisotropy are quantitatively evaluated by Bayesian analysis of the thermal diffuse scattering distribution. These results open a new possibility for directly characterizing nanoscale thermal properties in materials and devices, even those containing heavy elements such as thermoelectric materials.

First Principles Study of Electron Structure of La x Ba1- x MnO3 Crystals

In the framework of the density functional theory electronic band structure and density of states of LaxBa1-xMnO3 solid solutions containing different concentrations of La and Ba atoms, were studied using different exchange correlation functionals. Our calculation show that the band gap, which characterizes the properties of semiconductors, varies depending on the concentration of La and Ba atoms in the compounds. Using such a dependence, it is possible to make changes in physical properties depending on the concentration of cations.

Synthesis ranges for YBaFe4O7 and its topotactic oxidation in ambient air to YBaFeIII4O8.5

Conditions for YBaFe4O7 synthesis from oxide/carbonate amorphous precursors are investigated versus temperature and partial pressure of oxygen at high-temperature equilibrium with the sample in flowing atmosphere of humidified Ar and H2 gas mixtures. Upon topotactic oxidation in ambient air of the cooled-down product, YBaFeIII4O8.5 forms in a couple of minutes. Neutron powder diffraction suggests that added oxygens enter octahedral holes in the cubic closest packing of O and Ba atoms of YBaFe4O7. Up to two oxygen atoms add to some Fe coordination tetrahedra in the kagome-like layer of YBaFe4O7 in a disordered distribution described as partially occupied crystal-structure sites. The oxidized YBaFeIII4O8.5 is metastable and decomposes at high temperatures into FeIII oxides of barium or yttrium. The synthesized YBaFe4O7 is a powerful room-temperature O2 getter that can be reverted by annealing in the above gas mixture.

Effect of Ca substitution on crystal structure and band gap of solar cell material BaSi2

To ameliorate the potential of a promising solar cell material BaSi2, the effects of substituting Ba with Ca atoms on the crystal structure and band gap Eg of BaSi2, were investigated both experimentally and computationally. The solid-solution limit of the Ca atoms in BaSi2 was approximately 2.3 at.%. Single-crystal X-ray diffraction analysis of Ba1−xCaxSi2 (0.025 ≤ x ≤ 0.072) revealed that the unit cell volume decreases with Ca content x, and the Ba atoms at the A1 crystallographic site are preferentially substituted by Ca atoms. Diffuse reflectance measurements indicated that Eg decreases with x (1.24 eV at x = 0 and 1.17 eV at x = 0.07). The density functional theory calculations demonstrate that the experimentally observed decrease in Eg by Ca substitution can be explained qualitatively by the combination of the substitution of Ca atoms in the unit cell volume of BaSi2 and the volume reduction.

Synthesis and crystal structure of Ba2Y0.87(1)Mn1.71(1)Te5.

We report the structural characterization of a new quaternary telluride, Ba2Y0.87(1)Mn1.71(1)Te5, which was synthesized by the direct reaction of the elements inside a vacuum-sealed fused-silica tube. The quaternary phase is the first member of the Ba-M-Mn-Te system (M= Sc and Y). The composition and structure of the phase were elucidated using SEM-EDX (scanning electron microscopy-energy dispersive X-ray spectrometry) and single-crystal X-ray diffraction (SCXRD) studies. The title phase is nonstoichiometric and crystallizes in the monoclinic system (space group C2/m) having the refined unit-cell parameters a= 15.1466 (8), b= 4.5782 (3), c= 10.6060 (7) Å and β= 116.956 (2)°, with two formula units (Z= 2). The pseudo-two-dimensional crystal structure of Ba2Y0.87(1)Mn1.71(1)Te5 consists of distorted YTe6 octahedra and MnTe4 tetrahedra as the building blocks of the structure. The YTe6 octahedra are arranged to form infinite one-dimensional chains by sharing edges along the [010] direction. These chains are further connected to the MnTe4 tetrahedra along the c axis to create layered two-dimensional polyanionic [Y0.87(1)Mn1.71(1)Te5]4- units. The stuffing of Ba2+ cations in between the layers of [Y0.87(1)Mn1.71(1)Te5]4- anions brings the charge neutrality of the structure. Each Ba atom in the structure sits at the centre of a distorted monocapped trigonal prism-like polyhedron of seven Te atoms.

Color-tunable luminescence and temperature sensing properties of Bi3+/Sm3+ or Bi3+/Eu3+ codoped Ba2Gd2Ge4O13 phosphors.

Novel temperature-sensitive luminescent materials, Ba2Gd2Ge4O13 doped with Bi3+, Bi3+/Sm3+ or Bi3+/Eu3+ ions, have been prepared using a conventional solid-state reaction technique. The XRPD study has verified that all the synthesized germanates crystallize in the monoclinic system (space group C2/c, Z = 4). The crystal lattice of the compounds consists of zigzag chains of edge-sharing Me2O7 (Me = Bi3+, Eu3+ or Sm3+) dimers, [Ge4O13] units, and ten-coordinated Ba atoms. Under UV excitation the powders exhibit the luminescence corresponding to the 3P1 → 1S0 (310-550 nm) transition in Bi3+ and 4G5/2 → 6HJ (550-730 nm) in Sm3+ or 5D0 → 7FJ (570-720 nm) transitions in Eu3+ ions. Heating of Ba2Gd1.94Bi0.01Sm0.05Ge4O13 and Ba2Gd1.89Bi0.01Eu0.1Ge4O13 phosphors leads to an irregular decrease in the intensity of the main emission lines. It has been found that the fluorescence intensity ratio between a wide band in the 310-530 nm region and peaks at longer wavelengths may be successfully used as a temperature-dependent characteristic. Absolute/relative sensitivity values for Ba2Gd1.94Bi0.01Sm0.05Ge4O13 and Ba2Gd1.89Bi0.01Eu0.1Ge4O13 germanates reach 0.19% K-1/0.80% K-1 and 2.21% K-1/0.58% K-1, respectively. The above parameters indicate that Ba2Gd2Ge4O13:Bi3+/Sm3+ or Bi3+/Eu3+ samples can be used as potential luminescent materials for non-contact temperature measurement.