Ba 3d Research Articles

Exploring the physical properties of pristine γ-In2S3 and its influence on Ba doping for photocatalytic degradation of 2,4-D herbicide

In this work, pristine γ-In2S3 nanoribbons were synthesized using a facile solution process and uniquely doped with Ba for the first time. XRD and Raman spectroscopy confirmed the formation of pure-phase γ-In2S3 and successful Ba doping. XPS further validated the presence of Ba 3d core level with In 3d and S 2p after the inclusion of Ba. FESEM and HRTEM images showed the formation of nanoribbons, with the width increasing from 60 to 100 nm after doping. The anticipated stoichiometry of In and S, with approximately 2 atomic % of Ba, was confirmed by EDS. After Ba-doping, the bandgap was narrowed from 3.66 eV to 3.03 eV, and the charge carrier recombination was substantially reduced, as witnessed by PL and EIS. The potential of pristine γ-In2S3 and Ba-doped γ-In2S3 as new photocatalysts was highlighted in this study, exploring their applicability for the photodegradation of the stubborn herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The materials demonstrated impressive performances, achieving degradation efficiencies of 77.08 % and 94.15 % before and after doping, respectively, within 210 min. The scavenging tests revealed a significant contribution of O2•− and •OH for 2,4-D degradation using Ba-doped γ-In2S3 photocatalyst. Besides photocatalysts used in this study demonstrated excellent stability after four cycles. These findings suggest a promising approach for developing cost-effective semiconductors to remove persistent herbicides.

Exceptional behavior of a high-temperature superconductor in proximity to a ferromagnet in a bilayer film, La0.67Sr0.33MnO3/YBa2Cu3O7.

We studied the electronic properties of a high-temperature superconductor in proximity to a ferromagnetic material in a bilayer film of La0.67Sr0.33MnO3 (LSMO)/YBa2Cu3O7 (YBCO). High-quality single-crystalline films of YBCO and LSMO/YBCO were grown epitaxially on an SrTiO3 (001) surface. Magnetization data of the LSMO/YBCO bilayer exhibit ferromagnetic transition at about 255 K, which is much smaller than the Curie temperature of bulk LSMO. Experimental data show the emergence of magnetic anisotropy with cooling, which becomes significantly stronger in the superconducting phase. The onset temperature of diamagnetism is observed at 86 K in the YBCO sample for the out-of-plane magnetization and at 89 K in the in-plane data. Interestingly, the diamagnetism sets in at about 86 K for both magnetization directions in the LSMO/YBCO film despite the presence of the ferromagnetic LSMO layer underneath. Ba 4d and Y 3d core-level spectra show different surface and bulk electronic structures. Surface contribution is reduced significantly in the LSMO/YBCO sample, suggesting enhanced bulk-like behavior due to an enhancement of electron density near the surface arising from charge transfer across the interface. These results reveal an outstanding platform for on-demand tuning of properties without affecting the superconductivity of the system for the exploration of fundamental science and applications in advanced technology.

The relationship between orbital hybridization and superconductivity of sm-doped YBa2Cu3O7–δ studied by x-ray spectroscopy

Sm-doped YBa2Cu3O7–δ samples were prepared by conventional solid state reaction method in air. The studies of X-ray photoemission spectroscopy and X-ray absorption spectroscopy indicate that the extra electrons fill the holes in CuO2 planes, so that the hole carrier concentration decrease under Sm substitution. The X-ray absorption spectroscopy of Cu L-edge and O K-edge demonstrates that the hybridization strength between Cu 3d and O 2p decreases with increasing content of Sm, but the hybridization strength between Y 4d, Ba 5d, Sm 4f and O 2p increases with the increasing of Sm content, while the superconductivity of the Sm-doped YBa2Cu3O7–δ samples is suppressed, i.e., the superconducting transition temperature of the samples was lowered. Thus, our experimental results suggest a close relationship between the superconductivity and orbital hybridization.

Nature of the Ba 4d Splitting in BaTiO3 Unraveled by a Combined Experimental and Theoretical Study

Nature of the Ba 4d Splitting in BaTiO₃ Unraveled by a Combined Experimental and Theoretical Study

Synthesis, characterization, and sensitivity tests of a novel sensor based on barium antimonate powders

Barium antimonate (BaSb2O6) powders were prepared using a microwave-assisted wet chemistry process. The powders were calcined at 800 °C and their crystallinity was studied by X-ray diffraction, finding a hexagonal crystal structure with cell parameters a = 5.303 Å and c = 5.758 Å, and a P-31m (162) space group. Material’s morphology and particle size were analyzed by field-emission scanning and transmission electron microscopy, finding that nano-plates (~ 70 nm) and other apparently shapeless particles (~ 70 nm) were produced. By means of X-Ray Photoelectron Spectroscopy, it was found that the Ba 3d had a doublet (Ba 3d5/2 and Ba 3d3/2) with binding energies at 779.69 and 794.97 eV, respectively, which was associated with the Ba2+ oxidation state. The Sb 3d spectrum presented a doublet (Sb 3d5/2 and Sb 3d3/2) at 530.44 and 539.79 eV, while the O 1 s at 530.30 eV overlapped the Sb 3d5/2 peak. Photoacoustic Spectroscopy measurements of the oxide showed a band gap of 3.43 eV. Pellets manufactured with BaSb2O6’s powders calcined at 800 °C were tested in CO (1–300 ppm) and C3H8 (1–500 ppm) atmospheres at different operating temperatures (100, 200 and 300 °C). The pellets exhibited an excellent response, showing a high sensitivity as concentrations and temperature increased. Furthermore, the results indicated that the BaSb2O6 is highly selective to CO atmospheres. In particular, the good response of the pellets suggests that this oxide can be applied as a potential sensor for toxic gases.

Study of New Infrared Non-Linear Optical Crystal BaGa4Se7 Based on First Principle

The electronic structure and optical properties of BaGa4Se7 crystals were studied by generalized gradient approximation (GGA) and Heyd–Scuseria–Ernzerhof (HSE). The electronic structure results showed that BaGa4Se7 is a nonlinear optical crystal with a direct wide band gap. The band gap was calculated to be 2.36 eV using the HSE06 method, which is basically equal to the experimental value. The band structure showed that the top of the valence band was largely contributed by Ga 4s, 4p and Se 4p states, while the bottom of the conduction band was mainly comprised of Ga 4s, 4p, Se 4p, and Ba 5d states. The optical properties showed strong absorption and reflection in the ultraviolet region and strong transmittance in the infrared region. The average static refractive index of BaGa4Se7 was 2.73, and the static birefractive index was 0.04. These values indicate that the material has a good phase-matching ability and a wide laser damage threshold. The above results indicate that BaGa4Se7 is a potential infrared nonlinear optical crystal material.

DFT based investigations of BAWO4: Electronic and optical properties

Barium tungstate (BaWO4) has fascinating applications in the area of laser technology, solar cell, super capacitor, electronic devices and in photoluminescence. Electronic and optical behavior of BaWO4 is the reasons behind all of these fascinating applications. This research work provides the evaluation of electronic and optical properties of BaWO4 at the optimized cut-off energy value of 1200 eV by the implementation of Density Functional Theory (DFT) within the framework of CASTEP in Material STUDIO. The direct band gap and diamagnetic behavior of semiconductor BaWO4 have been evaluate by band structure, PDOS and TDOS calculation. O 2p of V.B and W, Ba 5d of C.B are the occupied electronic states of BaWO4. The highest band gap value of BaWO4 corresponds to highest loss function and smallest value of dielectric constant. Absorption spectrum exhibits that BaWO4 is an excellent UV absorber so it suitable for the formation of sensor, filter and for transparent conducting film for window layers on solar cell, solar control, and warming coatings. High refractive index value of BaWO4 makes it useful for detector for dark matter and for scintillators.

Theoretical Study of Infrared Nonlinear Optical Crystal BaGa4Se7 Tetragonal System

The electronic structure and optical properties of BaGa4Se7 tetragonal crystals are systematically studied by first principles of density functional theory. The band gap (2.918 eV) of the tetragonal system of BaGa4Se7 is 1.12 times that of the orthorhombic system by using the Heyd-Scuseria-Ernzerh (HSE06) method. The band structure showed that the top of the valence band was largely contributed by Ga 4s, 4p and Se 4p states, while the bottom of the conduction band was mainly comprised of Ga 4s, 4p, Se 4p, and Ba 5d states. This wide band gap effectively avoid the two-photon absorption during laser pumping and increase the laser damage threshold of the material. The orbital coupling between Ga and Se atoms determines the optical properties of BaGa4Se7 tetragonal crystals, while Ba atoms make little contribution to the optical properties. The calculation of optical properties shows that the static birefringence (0.076) of the BaGa4Se7 tetragonal crystal is 1.2 times that of the orthorhombic crystal system. It shows that the BaGa4Se7 tetragonal crystal material has excellent phase matching performance in a wide range of wavelengths. BaGa4Se7 crystal shows strong absorption and reflection characteristics in the ultraviolet region, and strong transmittance in the infrared region. Theoretical results indicate that BaGa4Se7 is a very promising nonlinear optical crystal in the infrared region.

Influence of Ca doping on X‐ray photoelectron core‐level spectra of magnetoelectric bulk BiFeO3

The X‐ray photoelectron spectrum (XPS) core‐level spectra of pristine and doped bulk BiFeO3, namely Bi0.9BaxCayFeO3 with x + y = 0 and 0.1 were recorded on the Ar+‐ion sputtered sample surface at room temperature. Afterward, the obtained XPS spectra of Bi 4f, Fe 2p, O 1 s, Ba 3d and Ca 2p levels were inspected using the symmetric Gaussian‐Lorentzian product function, to study the influence of the spin‐orbit coupling and/or electrostatic interactions on these spectra. Our findings show all elements have a single valence state (except Bi) with the allowed spin‐orbit splitting energy (Δ) for their valence of Bi3+, Fe3+, O2−, Ba2+, and Ca2+. Here, the fraction of Bi atoms was converted into Bi‐metal Bio, due to the Ar+‐ion sputtering process. Interestingly, the Fe3+ 2p3/2 spectra of these samples were fitted well with four Gupta–Sen multiplets, due to the combined electrostatic and spin‐orbit interactions. Particularly, the chemical pressure induced by Ca doping considerably influences the Fe3+ 2p3/2 spectra of BiFeO3, due to the change in the FeO6 octahedra tilting and the change in the position of Fe cations upon Ca doping. So, the edge of the valence band of the Ca‐doped BiFeO3 materials shifted toward the Fermi level by about ~0.7 ± 0.1 eV when compared to BiFeO3.

Oxidation processes at the surface of BaTiO3 thin films under environmental conditions

Dissociation and adsorption of water on ferroelectric oxide surfaces playimportant role in the processes of screening and switching dynamics of ferroelectric polarization, as well as in catalytic processes which can be additionally coupled with light, temperature or vibration stimuli. In this work,we present XPS study of ferroelectric BaTiO3thin films and determine the entanglement between surface chemistry, polarization direction and stability, by observing changes upon time exposure to environmental conditions, heating in O2atmosphereandirradiation in vacuum. We devote special attention to Ba 3d spectral region and identify two different oxidation states of O atoms in the compounds of Ba. While this second specie was generally attributed to Ba in surface compounds where it has different oxygen coordination than in the bulk, based on the XPS results of oxygen annealed thin films,we demonstrate that this so far neglected component, corresponds to barium peroxide (BaO2)and identify it as important active specie for the study of screening mechanisms closely related with catalytic activity present in this ferroelectric material. Finally, we report on chemically assisted polarization switching in thin films induced byheating in vacuum or exposure to X-Ray radiation due to the formation of positive surface electric field created by oxygen orelectron vacancies, respectively.

Ba with Unusual Oxidation States in Ba Chalcogenides under Pressure.

The preparation of compounds with novel atomic oxidation states and emergent properties is of fundamental interest in chemistry. As s-block elements, alkali-earth metals invariably show a +2 formal oxidation state at normal conditions, and among them, barium (Ba) presents the strongest chemical reactivity. Herein, we propose that novel valence states of Ba can be achieved in pressure-induced chalcogenides, where it also shows a feature of 5d-elements. First-principles swarm-intelligence structural search calculations identify three novel stoichiometric compounds: BaCh4 (Ch = O, S) containing Ba2+, Ba3Ch2 (Ch = S, Se, Te) with Ba+ and Ba2+, and Ba2Ch (Ch = Se, Te) with Ba+ cations. The pressure-induced drop of the Ba 5d level relative to Ba 6s is responsible for this unusual oxidation state. These compounds display captivating structural characters, such as Ba-centered polyhedra and chain-shaped Ch units. More interestingly still, the interaction between two Ba+ ions ensures their structural stability.

Enrichment of magnetoelectric effect in the hexagonal BaTi1-xCoxO3 artificial type-II multiferroics by defects

Artificial magnetoelectric material with enrichment of magnetoelectric (ME) coupling coefficient was achieved via mixed-oxide route in cobalt substituted BaTiO3 multiferroics. The observed large ME coupling coefficient induced by spin–orbit interaction through the symmetry breaking due to the off-stoichiometry oxygen. Structural details extracted from the Rietveld refinement indicate the rapid arrival of a single hexagonal phase (P63/mmc) at the expense of the tetragonal phase (P4mm) above x = 0.03. SAED patterns evidence to the structural coexistence, morphotropic phase boundary (MPB), (P4mm + P63/mmc) in x = 0.01 and 0.03 while hexagonal phase alone in x ≥ 0.05. Core-level XPS spectrum of Ba(3d), Ti (2p), Co (2p), O (1s) evidences the occurrence of the single oxidation state of Ba ion (Ba2+) and aliovalent of Ti (Ti4+ and Ti3+), Co (Co3+ and Co2+) and O (O2− and O1−) ions respectively. The weakening of ferroelectric loops arises from the formation of the non-ferroelectric hexagonal phase by the non-stoichiometric oxygen. For the first time, a high value of energy efficiency of 54.7% was achieved in the BaTi0.99Co0.01O3 sample. The ferromagnetism originated from the contributions of the super-exchange interaction of Co3+(octahedral)-O2−-Co3+(pentahedral) and double-exchange interaction (Co2+-O2−-Co3+) Among all the samples, an excellent magnetoelectric coupling coefficient (αME) value of 29.6 mV/cm Oe is attained in the hexagonal BaTi0.93Co0.07O3 sample.

Ab-initio investigations of electronic, optical, mechanical and thermal properties of Ca0.875Ba0.125Te

The ground-state properties and optical, mechanical, elastic and thermal properties of the Ca0.875Ba0.125Te alloy have been studied by using the full potential linearized augmented plane wave (FP-LAPW) scheme based on the density functional theory in the frame of generalized gradient approximation (GGA). In order to model Ca1-xBaxTe alloy, 16-atoms supercell of the type 2 × 2 × 2 is employed. The lattice structure of Ca0.875Ba0.125Te alloy is obtained by replacing one Ca atom by one Ba atom in the crystal lattice of CaTe. The charge density plot, electronic structure and density of states plots are made and discussed for the alloy. The lower valence band maxima (VBM) and the upper conduction band minima (CBM) of Ca0.875Ba0.125Te alloy is locaed at Γ point, ensuing in a direct band gap, whereas in case of parent element CaTe the nature of the band gap is indirect. The characteristic properties of Ca0.875Ba0.125Te alloy is dominated by Te 5p electrons (below the Fermi level) and Ba 4d and Ca 3d electrons (above the Fermi level).

Ab initio study of the electronic, elastic, vibrational and dielectric properties of KBaBi

KBaBi is predicted to be a topological insulator recently, but most fundamental properties of it have not been studied. In this work, first-principles calculations were carried out to study its electronic, bonding, elastic, vibrational and dielectric properties. The results indicate that KBaBi has a band gap of 0.22 eV with the presence of spin orbital coupling. Weak p-d hybridization exists between the Ba 5d and the Bi 6p orbitals, so KBaBi has some covalent property, as revealed by the electron density difference. Studies imply that KBaBi is mechanically and dynamically stable, but it is mechanically anisotropic. KBaBi has a theoretical bulk modulus of 20.8 GPa and a shear modulus of 11.7 GPa. Group theory analysis indicates that there are six infrared- and four Raman-active modes at the Brillouin zone center of KBaBi. The vibrational frequencies and the corresponding eigenvectors were calculated and discussed. Calculation unveils that the electrons have more dielectric contribution to the total dielectric constants than the ions in the ab plane, but it is revised along the c axis. Investigations of the band structure, the Debye temperature and the phonon dispersion curves indicate that KBaBi is a promising thermalelectric material.

Impact on Ferroelectricity and Band Alignment of Gradually Grown Au on BaTiO3

The competition between interface barrier in the Schottky–Mott limit and polarization driven mechanism is established during gradual formation of metal (Au) – ferroelectric (BaTiO3) interface. X‐ray photoelectron spectroscopy provides core level energies and valence band positions in the contact region, to monitor the band alignment from the very first stages of metal deposition on BaTiO3. The band bending at metal/ferroelectric (FE) interface is extracted from the shift of core levels (Ba 3d, Ti 2p) as a function of the metal thickness. It is shown that the interface band alignment mechanism involves a well‐defined polarization orientation washing out the bending expected from the work function difference. The sudden modification of the binding energies within ferroelectric at the first 2 Å Au indicates that the ferroelectric compensation mechanism triggered by the metal overlayer initiates already at ultrathin top layer, while subsequent growth contributes only at a gradual correction of the potential in the FE. The emerging picture is confirmed in first‐principle calculation indicating the preferences of Au to grow preferentially to different terminated regions and to stabilize distinct ferroelectric polarization.

Soft X-ray photoemission study of Ba adsorption on the ceramic multiferroic BiFeO3

Electronic structure of the ceramic multiferroic BiFeO3 and ultrathin Ba/BiFeO3 interface was studied in situ using photoelectron spectroscopy with energies in the range of 120–900 eV. The photoemission from the Bi 4f, O 1s, Fe 2p, and Ba 4d core levels was studied. An effect of Ba adsorption is found to induce a significant change in all spectra that is originated from the strong interaction with the charge transfer between Fe, O, Bi surface atoms and Ba adatoms. The recharge between Fe3+↔ Fe2+ ions in surface region induced by Ba adsorption is found that provide enhancing the ferroelectric polarization gain.

Stress dependence of structure, electronic and optical properties of BaTiO3 from WC, VdW-DF-C09 and HSE functional calculations

The optimization of a BaTiO3 crystal unit cell was realized with the WC and VdW-DF-C09 exchange-correlation functional, under different hydrostatic pressures from –10 to 10 GPa with step size of 5 GPa. As part of the results, changes in the crystal lattice parameters and volume are presented and discussed, as well as changes in the different Ba-O and Ti-O bond lengths. Self-consistent calculations (SCF) were performed using HSE functional in order to obtain electronic band structure, density of state (DOS) and optical properties. Löwdin charge analysis, related to charge transfer of Ba, Ti, and O, shows the details of the atomic bonds as function of the hydrostatic stress, including the contribution of empty orbits such as the 6p, 5d and 4f from Ba atoms, 3d and 4f from Ti atoms and 3d and 4f from O atoms. Finally, the imaginary part of the complex dielectric function, in the energy range from 0 to 15eV, is presented and discussed.

Evidence for absence of metallic surface states in BiO2-terminated BaBiO3 thin films

We investigated the atomic configuration and the electronic structure of a BaBiO3 (BBO) thin film and its (001) surface. It was theoretically predicted that two-dimensional electron gases would be formed when the film is BiO2-terminated. We deduced depth-profile information for a BBO thin film using angle-dependent X-ray photoemission spectroscopy. Analysis of the spectral weights of the Ba 3d and Bi 4f core levels confirmed that the BBO film should have a BiO2-terminated topmost layer. We used in-situ angle-resolved photoemission spectroscopy to experimentally determine the electronic structure of a BBO thin film and found no metallic surface state. We distinguished surface states from bulk states by evaporating potassium atoms in-situ on the surface. A surface state near the bottom of the topmost bulk valence band, which was predicted by the DFT calculations, was identified. However, other surface states well separated from the bulk states were not observed. Our results provided evidence that descriptions of the BBO electronic structure require more detailed and elaborate approaches.

Synthesis and Crystal Structure of the Layered Lanthanide Oxychlorides Ba3Ln2O5Cl2.

Single crystals of a new family of layered lanthanide oxychlorides, Ba3Ln2O5Cl2 (Ln = Gd-Lu), have been synthesized from a molten barium flux. This family crystallizes in the space group I4/mmm (No. 139; Z = 2) with lattice parameters a = 4.3384(1)-4.4541(1) Å and c = 24.5108(7)-24.8448(9) Å. Ba3Ln2O5Cl2 phases are built up of two different blocks: a perovskite double layer of stoichiometry Ba2Ln2O5 formed by corner-connected LnO5 tetragonal bipyramids and a puckered rock-salt-like interlayer of composition BaCl2. A complete structural study along with bond-valence-sum calculations shows that, for lanthanides larger than gadolinium, the structure becomes unstable. Density functional theory calculations show that the valence-band edge is dominated by oxygen orbitals, whereas the conduction band forms from Ba 5d orbitals. The synthesis of this family suggests a route to other potential multianion phases.

Soft X-ray photoelectron spectroscopy of the ultrathin Ba/InGaN interface

Electronic structure of the clean In0.22Ga0.78N surface and the ultrathin Ba/In0.22Ga0.78N interface has been studied in situ by the synchrotron-based photoelectron spectroscopy during excitation in the photon energy range of 100–650eV. Changes in the valence band and surface states spectra and in the In 3d, In 4d, N 1s, Ga 3d, Ba 4d, Ba 5p core levels spectra have been investigated under the step-by-step Ba submonolayer deposition. Changes in the surface electronic structure of the InGaN caused by Ba adsorption are found to originate predominantly from the local interaction of the Ga and In dangling bonds and Ba adatoms that results in effect of the suppression of the two intrinsic surface states and appearance of a new induced state. The Ba atomic layer deposition is revealed to induce the charge transfer between the Ba adatoms and the N surface atoms with increasing N-ionicity.