Ba Doping Research Articles

Enhanced photoreversible color switching of redox dyes catalyzed by barium-doped TiO2 nanocrystals.

Colloidal barium-doped TiO2 nanocrystals have been developed that enable the highly reversible light-responsive color switching of redox dyes with excellent cycling performance and high switching rates. Oxygen vacancies resulting from the Ba doping serve as effective sacrificial electron donors (SEDs) to scavenge the holes photogenerated in TiO2 nanocrystals under UV irradiation and subsequently promote the reduction of methylene blue to its colorless leuco form. Effective color switching can therefore be realized without relying on external SEDs, thus greatly increasing the number of switching cycles. Ba doping can also accelerate the recoloration under visible-light irradiation by shifting the absorption edge of TiO2 nanocrystals to a shorter wavelength. Such a system can be further casted into a solid film to produce a rewritable paper on which letters and patters can be repeatedly printed using UV light and then erased by heating; this process can be repeated for many cycles and does not require additional inks.

Synthesis and photoactivity enhancement of Ba doped Bi2WO6 photocatalyst

In this study, Bi2WO6 doped with different barium contents were successfully prepared by a simple hydrothermal route at 180°C for 12h. The as-synthesized samples were characterized in detailed by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffusere flectance spectroscopy (UV–vis DRS) and Brunauer–Emmet–Teller (BET) theory. Their photocatalytic activities were evaluated by photodegradation of Rhodamine B (RhB) under simulated solar light. As a result, the photocatalytic properties were enhanced after Ba doping and the Ba-doped Bi2WO6 with RBa=0.15 showed the highest photocatalytic activities of 96.3% RhB was decomposed in 50min. Close investigation revealed that the proper Ba doped into Bi2WO6 could not only increases its BET surface area, decrease its crystalline size, but also act as electron traps and facilitate the separation of photogenerated electron–hole pairs. The mechanism of enhanced photocatalytic activities of Ba-doped Bi2WO6 were further investigated.

Ba2phenanthrene is the main component in the Ba-doped phenanthrene superconductor.

We have systematically investigated the crystal structure of Ba-doped phenanthrene with various Ba doping levels by the first-principles calculations combined with the X-ray diffraction (XRD) spectra simulations. Although the experimental stoichiometry ratio of Ba atom and phenanthrene molecule is 1.5:1, the simulated XRD spectra, space group symmetry and optimized lattice parameters of Ba1.5phenanthrene are not consistent with the experimental ones, while the results for Ba2phenanthrene are in good agreement with the measurements. The strength difference of a few XRD peaks can be explained by the existence of pristine phenanthrene. Our findings suggest that instead of uniform Ba1.5phenanthrene, there coexist Ba2phenanthrene and undoped phenanthrene in the superconducting sample. The electronic calculations indicate that Ba2phenanthrene is a semiconductor with a small energy gap less than 0.05 eV.

Structural and electrical behavior of Ba-doped LaGaO3 composite electrolyte

In the present work, Ba-doped lanthanum gallate (La1−xBaxGaO3−δ with x = 0, 0.05, 0.10, 0.15, 0.20) have been prepared by solid-state reaction method. X-ray diffraction confirms the formation of perovskite structure with orthorhombic symmetry. Furthermore, Ba doping leads to partial stabilization of rhombohedral phase at room temperature. In addition, the grain size of perovskite phase (LaGaO3) decreased with Ba-dopant. La0.85Ba0.15GaO3−δ exhibits the highest conductivity of the order of 6 × 10−3 S cm−1 at 800 °C. The rhombohedral phase formation also enhances the ionic conductivity of the composite system. The calculated activation energy for all the doped samples varied from 0.62 to 0.66 eV in the temperature range of 600 to 800 °C, which indicates that the conduction behavior is mainly ionic. Coefficient of thermal expansion for La0.85Ba0.15GaO3−δ is 10.8 × 10−6 °C−1 from 600 to 800 °C, which is in the range required for solid oxide fuel cell applications.

Enhanced luminescence properties in (Sr1−xBax)2.97SiO3N4/3:0.03Eu2+ oxynitride phosphor

An oxynitride phosphor (Sr1−xBax)2.97SiO3N4/3:0.03Eu2+ (SBSON) was synthesized by the solid-state reaction at 1550°C for 4h. XRD results show that the major phase of the synthesized phosphors is isostructural with Sr3SiO5 when the content of Ba2+ is not greater than 0.5. Through the doping of Ba2+ ions, the particle morphology, luminescence intensities and thermal stability are all improved obviously. When the x equals 0.5 the luminescence intensity reaches maximum which is about 1.48 times as that of the phosphor free of Ba2+. The emission peaks can be tuned from 583nm to 601nm by adjusting Ba2+ content. The doping of Ba2+ can also prolong the average lifetime from 1482 to 2122ns. With high emission intensity and thermal stability, this novel oxynitride phosphor SBSON shows potential application in white LEDs.

First-Principles Study of Barium and Zirconium Stability in Uranium Mononitride Nuclear Fuels

Barium and zirconium solution behaviors in antiferromagnetic uranium mononitride (UN) have been studied based on first-principles density functional theory. By calculating the incorporation and solution energies in UN, it is found that the most favorable solution sites are U vacancies for both Ba and Zr, and Zr is more soluble than Ba. The volume of the Ba-doped system keeps expanding with increasing Ba doping concentration, whereas that of the Zr-doped system changes from swelling to contraction with increasing Zr doping concentration. This phenomenon may result from the difference of these two elements in atom radius and coordination mechanism. Furthermore, the solution energies of metallic and nitride phases of Ba and Zr indicate that both phases of Ba are insoluble in the UN matrix, whereas the metallic phase of Zr is insoluble, and its nitride ZrN is soluble in the UN matrix.

A new family of barium-doped Sr2Fe1.5Mo0.5O6−δ perovskites for application in intermediate temperature solid oxide fuel cells

Sr2−xBaxFe1.5Mo0.5O6−δ (x = 0, 0.2, 0.4, 0.6, 0.8, 1) perovskite materials have been prepared as potential cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs) via a sol–gel combustion method. X-ray diffraction (XRD) confirms that the expansion of the unit cell derived from the substitution of the large radius Ba atom, with the impurity phase structure only being detected when x = 0.8 and 1. Concurrently, thermal expansion coefficients (TECs) increase with increasing Ba doping. X-ray photoelectron spectrometry (XPS) measurements show that A-site doped Ba in the perovskite has an insignificant impact on the existence and ratio of Fe2+/Fe3+ and Mo6+/Mo5+ species within the Sr2−xBaxFe1.5Mo0.5O6−δ (x = 0.2, 0.4, 0.6) (SBFM) samples. Compared with Sr2Fe1.5Mo0.5O6−δ, the SBFM cathodes exhibited better electrochemical performance, which has been confirmed by the electrochemical impedance spectra (EIS). In particular, Sr1.8Ba0.2Fe1.5Mo0.5O6−δ (SB0.2FM) shows the lowest interface polarization (Rp). Furthermore the peak power densities of single cells based on the SB0.2FM cathode are 0.87 and 1.30 W cm−2 at 700 and 750 °C, respectively. All these results suggest that SBFM materials are promising cathodes for IT-SOFCs.

High Tc ferroelectricity in Ba-doped ZnO nanoparticles

Effects of Ba doping on structural, optical and ferroelectric properties of ZnO nanoparticles prepared by a low cost thermal decomposition method are presented. The substitution of Ba on Zn sites of the wurtzite structure of ZnO was observed by X-ray diffraction. Some structural transformation in the morphology of nanostructure with Ba doping was observed. Redshift in band gap is observed in the UV–visible spectra after Ba doping, supported by photoluminescence spectra and showing enhanced defect states with Ba doping. In dielectric studies, high value of dielectric constant and transition temperature at (~330°C) were observed. High value of remnant polarization (1.01µCcm−2) and low value of coercive field (2.02kVcm−1) were also observed in ferroelectric studies which can be useful for potential applications.

Enhanced Thermoelectric Properties of Hole-Doped Bi2−x Ba x Sr2Co2O y Ceramics

The influence of Ba doping on the thermoelectric properties of Bi2−x Ba x Sr2 Co2O y (x = 0.00, 0.025, 0.05, 0.075, 0.10, 0.125, and 0.15) samples prepared by the solid-state reaction method was investigated from 333 K to 973 K. For the samples with x ≤ 0.075, the electrical resistivity decreased with increase of the Ba doping amount due to p-type doping and they exhibited metallic electrical conductivity behavior, whereas the samples with x ≥ 0.10 exhibited semiconductor-like electrical conductivity behavior. The Seebeck coefficients of all the samples decreased with increase of the Ba doping amount. The thermal conductivity first decreased for x ≤ 0.075, then increased with higher Ba doping amounts. As an overall result, the dimensionless figure of merit (ZT) of Bi1.925Ba0.075Sr2Co2O y reached the maximum value of 0.245 at 973 K, being 41% higher than that of the undoped sample.

STUDY ON ABNORMAL PHENOMENON ABOUT ENHANCED ELECTRICAL CONDUCTIVITY OF Bi1-xBaxFeO3 CERAMICS

In order to investigate the effects of Ba doping BiFeO 3 on multiferroic properties, Bi 1-x Ba x FeO 3(0≤x≤1)( Ba x BFO ) ceramics were fabricated via rapid solid phase sintering method, and material's structures and electrical properties were investigated. The phase transitions from rhombohedral to pseudo-cubic (x = 10%) and then to tetragonal (x = 40%) were confirmed by X-ray diffraction investigation. Although the electrical conductivity of Ba x BFO (x = 10%, 20% and 30%) ceramics was low, which is a similar trend to previous reports, an abnormal enhancement of electrical conductance was observed in Ba x BFO (x = 1%, 3% and 5%) ceramics. Such as, the electrical conductivity of Ba 0.03 BFO is calculated to be ~106 Ω⋅ cm that is five orders of magnitude higher than that of the BiFeO 3. This has been discussed and ascribed to more percent of oxygen vacancies and Fe 2+ ions in Ba x BFO ceramics, as confirmed by X-ray photoelectron spectroscopy investigation.

Evidence for excluding the possibility ofd-wave superconducting-gap symmetry in Ba-doped KFe2As2

We have investigated the superconducting (SC)-gap anisotropy for several Ba-doped KFe${}_{2}$As${}_{2}$ samples using laser-based angle-resolved photoemission spectroscopy. We show that the SC-gap anisotropy and node positions drastically change with a small amount of Ba doping. Our results totally exclude a possibility of $d$-wave symmetry and strongly suggest that both spin and orbital fluctuations are important for the pairing interaction in the Ba-doped K122.

High Dielectric and Electrical Properties of CuO Doped (Ba0.5Sr0.5)TiO3 Ceramics

The effects of CuO additions on the sintering temperature and dielectric properties of (Ba0.5Sr0.5)TiO3 ceramic have been investigated by employing X-ray diffraction analysis, scanning electron microscopy, and dielectric properties measurements. In this research, 1–5 wt% CuO was added to the (Ba0.5Sr0.5)TiO3 powders to reduce the sintering temperature. CuO-doped (Ba0.5Sr0.5)TiO3 ceramics were sintered from 750 to 1350°C to confirm the sintering temperature with various dopants, respectively. It was found that the addition of CuO to (Ba0.5Sr0.5)TiO3 could lower the sintering temperature from 1350 to 1150°C. Moreover high dielectric permittivity was observed in the 5 wt% CuO doped (Ba0.5Sr0.5)TiO3 ceramics.

Effect of Na Content on the Physical Properties ofBa0.5Sr0.5TiO3Powders

The different Na contents (0 ≤ Na ≤ 0.35, based on mole of NaOH) of doped Ba0.5Sr0.5TiO3(BST) powders synthesized via sol-gel process were studied. The substitution of Na+ions into a partial A-site of BST powders provided the reduction in vacancy defects as confirmed by electron paramagnetic resonance (EPR) and UV-visible spectroscopy. Photoluminescence (PL) spectra appeared in violet, blue, and green emissions. The phase structure, oxygen deficiency, and titanium deficiency of BST powders were further investigated as a function of Na content. X-ray diffraction (XRD) result was found that low Na content (0 ≤ Na ≤ 0.15) exhibited the tetragonal structure, while it was transformed to the cubic phase when high Na content. Moreover, X-ray photoelectron spectroscopy (XPS) result revealed that the partial oxidation of Ti3+ions to Ti4+ions was observed at Na content lower than 0.05 mole, while more addition of Na content resulted in the increasing of the oxygen and the titanium deficiency. Furthermore, the result indicated the oxygen deficiency significantly formed at the A-site of Sr atoms more than that of Ba atoms.

Influence of Barium Doping on Physical Properties of Zinc Oxide Thin Films Synthesized by SILAR Deposition Technique

Undoped and Barium (Ba) doped ZnO thin films were deposited on glass substrates by successive ion layer adsorption and reaction (SILAR) method using zinc acetate, barium chloride and ammonium hydroxide solution. In the present work the effect of Barium doping on structural, optical and morphological properties were investigated. Structural characterization by X-ray diffraction reveals that ZnO films are polycrystalline with wurtzite structure. SEM images showed that Ba doping influenced surface morphology and grain size was found to increase with increase in doping level. Optical analysis showed that all the films had good transmittance in the visible region. The presence of defects into ZnO films was detected through photoluminescence studies.

Possible nodal superconducting gap and Lifshitz transition in heavily hole-doped Ba0.1K0.9Fe2As2

We performed a high energy resolution ARPES investigation of over-doped Ba0.1K0.9Fe2As2 with T_c= 9 K. The Fermi surface topology of this material is similar to that of KFe2As2 and differs from that of slightly less doped Ba0.3K0.7Fe2As2, implying that a Lifshitz transition occurred between x=0.7 and x=0.9. Albeit for a vertical node found at the tip of the emerging off-M-centered Fermi surface pocket lobes, the superconducting gap structure is similar to that of Ba0.3K0.7Fe2As2, suggesting that the paring interaction is not driven by the Fermi surface topology.

Polarization‐Induced Photoluminescence Quenching in (Ba0.7Ca0.3TiO3)–(BaZr0.2Ti0.8O3):Pr Ceramics

Pr3+‐doped (Ba0.85Ca0.15)(Zr0.1Ti0.9)TiO3 ceramics were prepared by a solid‐state reaction method. The effects of doping concentration, sintering temperature, and ferroelectric remanent polarization on photoluminescence (PL) properties of samples were systematically investigated. The PL spectra of samples exhibit strong green and red emissions with a broad blue excitation band ranging from 430 to 500 nm, in a good agreement with all commercial blue LEDs emission wavelength. Except for the concentration and temperature PL quenching, the polarization‐induced PL quenching was obviously observed, and the degree of PL quenching changes with Pr3+ concentrations, the origin of the change is well interpreted by field‐induced structural phase transitions between rhombohedral (R3m) and tetragonal (P4mm) for BCZT: xPr ceramics near the morphotropic phase boundary.

Magnetic and Photocatalytic Behaviors of Ba‐Doped BiFeO3 Nanofibers

BiFeO3 nanofibers doped with divalent barium have been fabricated using electrospinning technique. Phase transition from space group R3c to C222 can be observed by the Ba doping. Our results indicate that these BiFeO3 nanofibers show obvious room temperature ferromagnetic behaviors, which can be enhanced remarkably with the increment of Ba doping. Microstructure and composition analysis indicates that barium effectively affected the magnetism after doping content was more than 5% and optical properties.

Electronic and magnetic properties of a new 2D diluted magnetic semiconductor La1 − x Ba x Zn1 − x Mn x AsO from Ab initio calculations

Very recently, on the example of hole- and spin-doped semiconductor LaZnAsO, quite an unexpected area of potential applications of quasi-two-dimensional 1111-like phases was proposed (C. Ding et al., Phys. Rev. B 88, 041102R (2013)) as a promising platform for searching for new diluted magnetic semiconductors (DMSs). In this work, by means of the ab initio calculations, we have examined in detail the electronic and magnetic properties of LaZnAsO alloyed with Ba and Mn. Our results demonstrate that Ba or Mn doping transforms the parent non-magnetic semiconductor LaZnAsO into a non-magnetic metal or a magnetic semiconductor, respectively. On the other hand, the joint effect of these dopants (i.e., co-doping Ba + Mn) leads to transition of La0.89Ba0.11Zn0.89Mn0.11AsO into the state of magnetic metal, which is formed by alternately stacked semiconducting non-magnetic blocks [La0.89Ba0.11O] and metallic-like magnetic blocks [Zn0.89Mn0.11As].

Crystallite structure, microstructure, dielectric, and piezoelectric properties of (Pb1.06−xBax)(Nb0.94Ti0.06)2O6 piezoelectric ceramics prepared using calcined powders with different phases

In an attempt to obtain dense lead metaniobate-based ceramics with improved dielectric and piezoelectric properties, the (Pb1.06−xBax)(Nb0.94Ti0.06)2O6 (x = 0, 0.04, 0.08, 0.12) piezoelectric ceramics were prepared separately from the two kinds of calcined powders, i.e., the powders with the rhombohedral phase and orthorhombic phase. For obtaining the calcined powders with the different phases, two different calcination temperatures of 900 °C and 1250 °C were chosen. The calcined powders were characterized using X-ray diffraction, scanning electron microscope, laser particle size analyzer and differential scanning calorimetry. Effects of the phase structures of the calcined powders on crystallite structure, microstructure, dielectric and piezoelectric properties of the ceramics were studied in detail. The lattice parameters and grain size of the ceramics are related to the phase structures of the calcined powders. The doping of Ba2+ has an influence on the dielectric and piezoelectric properties of the ceramics. The ceramics with x = 0.08 fabricated from the calcined powders with the orthorhombic phase demonstrate the optimum dielectric and piezoelectric properties.

Modeling the paraelectric aging effect in the acceptor doped perovskite ferroelectrics: role of oxygen vacancy

The time dependence of physical properties in the paraelectric phase was probed recently in a Mn3+ doped (Ba0.8Sr0.2)TiO3 ceramic, providing a simple situation (without spontaneous polarization or domain walls) to quantify the role of the oxygen vacancy during aging. In the present study, we propose a quantitative model for paraelectric aging to understand how the distribution of the oxygen vacancy evolves with time and consequently influences the dielectric response of the paraelectric phase. First, by comparing dielectric behavior of paraelectric aging in a Mn3+ doped (Ba0.75Sr0.25)TiO3 ceramic and the dielectric tunable effect, an internal bias field Ein related to the oxygen vacancy is shown to exist in the paraelectric phase. Second, by introducing such a time dependent Ein in a Landau-type model, we reproduce the dielectric response of Mn3+ doped (Ba0.8Sr0.2)TiO3 ceramic during paraelectric aging. It is suggested that the increase of dielectric permittivity can be ascribed to the decrease of Ein with time. The investigation of paraelectric aging is helpful for understanding the role of the oxygen vacancy in influencing the physical properties of ferroelectric materials.