Barium Halides Research Articles

Fundamentals of Flexoelectricity, Materials and Emerging Opportunities Toward Strain-Driven Nanocatalysts.

Flexoelectricity, an intrinsic property observed in materials under nonuniform deformation, entails a coupling between polarization and strain gradients. Recent catalyst advancements have reignited interest in flexoelectricity, particularly at the nanoscale, where pronounced strain gradients promote robust flexoelectric effects. This paper comprehensively examines flexoelectricity, encompassing methodologies for precise measurement, elucidating its distinctions from related phenomena, and exploring its potential applications in augmenting catalytic properties. So far, the greatest potentials are based on lead strontium titanate (PST) and other metallic titanates such as titania (TiO2), strontium titanate (STO), barium strontium titanate (BST) sulfates (MoS2, ZnS)and halide perovskites (with archetype XPbI3). This review explores the promise of flexoelectric properties in addressing material and photocatalytic challenges, such as charge carrier recombination and ineffective surface charge separation. Additionally, it sheds light on the synergy with emerging paradigms like photo-flexo catalysis and synergistic flexo-piezo catalysis, specifically focusing on selective chemical transformations like green hydrogen production. Current limitations related to the usage of photoflexoelectricity for photocatalysis are mostly the stability of the used substance (susceptibility to photodegradation) or the voltage values, which represent the inferior potential for specific practical applications. This work underscores the indispensable role of flexoelectricity in catalysisand its capacity to steer future researchand technological advancement.

Correlation of cation-anion radii ratio with physical and electronic properties of scintillator materials barium dihalides (BaX2, X = F, Cl, Br, I): DFT calculations and experimental results

The physical, electronic and optical properties of Barium halides have been investigated by both experimental and theoretical approaches. The First Principle electronic structure and optical properties were calculated by DFT formalism using Full Potential Linearized Augmented Plane Wave plus local orbitals (FP-LAPW + lo) implementing different appropriate exchange-correlation functionals in WIEN2k code at various applied volumetric pressure up to 50 GPa. All the properties of these halides were analyzed and compared using their cation-anion radii ratio and ionicity. Except BaF2, the other three halides show ionic to covalent transformation at 50 GPa applied pressure. Both experimental and theoretical results compare reasonably well. The scintillation efficiency of these three halides was found to be directly proportional to their ionicity or band gap.

Feasibility study of Phosphor material synthesis process based on Barium halides via hydrothermal technique

Barium halides based was typical host for phosphor material applied as imaging plate for computed radiography application. In this study, the host phosphor materials based on barium halides has been synthesized via hydrothermal technique. The aim of this study is to determine the feasibility of hydrothermal technique to synthesis phosphor materials. Three samples have been prepared for this study. All samples had fix Ba and Br composition but was differentiated by the third composition i. e F, Cl and I. X-ray diffraction (XRD) technique has been used to determine the crystallinity of the prepared samples while optical property was observed using photoluminescence (PL) spectroscopy. The sharp, narrow and high intensity peaks from XRD diffractogram showed that all samples have good crystallinity. The PL spectrum indicated that the emission of all samples corresponds to blue range. This study proved that hydrothermal method was feasible for phosphor materials synthesis process based on barium halides and offered lower temperature with shorter period of heating process which is cost effective for synthesis process.

Elucidating the effect of barium halide promoters on La2O3/CaO catalyst for oxidative coupling of methane

The industrialization of oxidative coupling of methane (OCM) is restricted by the low once through yield of C2 hydrocarbons. Recently, the halogen-assisted OCM process has been attempted to overcome this issue, but the reaction stability was poor due to the rapid loss of gas-phase halides or molten alkali halides. In this work, the barium salts, particularly barium halides (BaCl2 and BaF2), were demonstrated to be efficient promoters to improve the OCM reactivity of La2O3/CaO catalyst by increasing both C2 selectivity and C2H4/C2H6 ratio, and simultaneously achieving outstanding reaction stability. The promoting mechanism can be understood in two aspects. On the one hand, the introduction of barium salts increased the amount of surface electrophilic oxygen species, serving as the alkaline active sites for selective methane activation. On the other hand, the barium halide additives induced the in-situ formation of methyl halide intermediates facilitating C2H6 dehydrogenation, and their intimate contact with catalyst substrate restricted the rapid halogen loss and thereby improved the catalytic stability. This work not only provides a class of efficient OCM catalyst, but also offers a highly stable halogen-assisted reaction strategy.

High pressure nanoarchitectonics and metallization of barium chloride and barium bromide

As one of the most prototypical AX 2-type compounds, barium halide shared the cubic structure with Fm−3m symmetry for BaCl2 or orthorhombic structure with Pnma symmetry for BaBr2 at ambient pressure. In this work, we explored the crystal structures of BaCl2 and BaBr2 under high pressure. We predicted a thermodynamically more favored structure with orthorhombic Cmcm symmetry for both BaCl2 and BaBr2, at 74 and 47 GPa, respectively. Our simulations reveal that the metallic feature of Cmcm BaCl2 and Cmcm BaBr2 under high pressure. The present results improve the understanding of high-pressure structures of AX 2 compounds at extremely high-pressure conditions.

The enhancement effects of BaX2 (X = F, Cl, Br) on SnO2-based catalysts for the oxidative coupling of methane (OCM)

In this study, the promotional effects of different barium halides (BaF2, BaCl2 and BaBr2) on SnO2 for OCM reaction have been investigated. It is observed that the addition of all the barium halides can improve the reaction performance of SnO2, following the sequence of BaBr2 > BaCl2 > BaF2. Raman and XRD results have substantiated that adding barium halides to SnO2 can increase the amount of surface vacancies/defects, hence creating more abundant surface OCM reactive oxygen sites by anion substitution. At the same time, the amount of the moderate basic sites contributing to OCM reaction is also improved. During OCM reaction, the amount of the OCM reactive oxygen species as well as the moderate basic sites can be further increased. As proved by In situ Raman and XPS results, on BaF2:SnO2 = 1:1 and BaCl2:SnO2 = 1:1, O2− is the OCM reactive oxygen sites. In contrast, on BaBr2:SnO2 = 1:1, O22- is the OCM reactive oxygen sites, which is induced by the formation of BaSnO3 perovskite phase. Moreover, O22- anions are reported to be favourable for the direct formation of C2H4 through carbene mechanism, which explains the high ethylene selectivity on BaBr2-modified catalyst. The amount and properties of the surface active oxygen species and basic sites are of great importance for OCM reaction, and their concerted interaction determines the reaction performance of BaX2/SnO2 catalysts. BaBr2:SnO2 = 1:1 contains the apporiate amount of both types of active sites, hence displaying the best OCM performance among all the catalysts.

DFT calculations of structural, electronic, optical and elastic properties of scintillator materials BaCl2 and BaBr2

Detailed structural, electronic, optical and elastic properties with their pressure dependence of two barium halide scintillators are presented using first-principles calculations based on the density functional theory formalism. Only PBE-GGA results tally the closest with experimental results of a band gap of 4.26 eV for BaBr2 and 4.96 eV for BaCl2. The electron () and hole () effective masses are determined to be 0.88 and 0.95 for BaCl2 and 0.86 and 0.91 for BaBr2. The pressure dependence yields the pressure coefficient of the band gap as −4.34 × 10−2 eV GPa−1 and −3.77 × 10−2 eV GPa−1 for BaBr2 and BaCl2, respectively. All the elastic constants and the related parameters are calculated for both the halides. The optical and elastic properties clearly indicate the anisotropy along the three crystallographic directions of these two scintillators. The scintillation properties of the two compounds with and without doping are discussed in the light of these properties.

ChemInform Abstract: α‐Selective Allylation of Azo Compounds Using Allylic Barium Reagents.

AbstractThe organobarium reagents are prepared in situ from reactive Riecke barium and allylic halides.

ChemInform Abstract: New Ternary and Quaternary Barium Nitride Halides; Synthesis and Crystal Chemistry.

AbstractBa2NF (I), Ba2NCl (II), Ba2NCl0.8Br0.2 (III), Ba2NCl0.6Br0.4 (IV), Ba2NCl0.4Br0.6 (V), Ba2NCl0.2Br0.8 (VI), Ba2NBr (VII), and Ba2NBr0.8I0.2 (VIII) are prepared by reaction of the respective barium halides BaX2 (X: F, Cl, Br, I) with Ba2N (998 K, 5 d).

New Ternary and Quaternary Barium Nitride Halides; Synthesis and Crystal Chemistry

New ternary and quaternary nitride halides, Ba(2)N(X,X') (X = F, Cl, Br; X' = Br, I), have been synthesized from the high temperature reactions of barium subnitride with the respective barium halides under an inert atmosphere. The former include the first fully characterized barium nitride halides for X other than F, and the latter are the first examples of barium nitride mixed halides. The variation in structure with composition has been investigated by powder X-ray and powder neutron diffraction techniques. The heavier ternary and quaternary nitride halides (X, X' = Cl, Br, I) crystallize in the hexagonal space group R3m, with the anti-α-NaFeO(2) structure. Ba(2)NF forms with both an anti-α-NaFeO(2) structure, in which N(3-) and F(-) are ordered and an anion-disordered simple rock salt structure. The hexagonal polymorph of Ba(2)NF is the only example to date of a nitride fluoride adopting this layered structure. Both the ternary and the quaternary compounds display very weak, temperature independent paramagnetism.

Composites “binary salts in porous matrix” for adsorption heat transformation

A family of Composites “Salt inside Porous Matrix” (CSPM) has been considered as promising for adsorption heat transformation (AHT) due to their high sorption capacity, steep sorption isobars and opportunity to harmonize CSPM properties with boundary conditions of the AHT cycle. In this communication, we extend the harmonizing tools by confinement of one more salt to the matrix pores. Novel CSPMs based on a binary mixture of lithium, calcium, and barium halides inside various mesoporous matrices were synthesized with wide variation of the relative salts content. Their phase composition and sorption equilibrium with water, methanol and ammonia vapour were studied by XRD and TG techniques. It was shown that the formation of a homogeneous solid solution of the salts led to changing the equilibrium temperature (pressure) of the solvation. Thus, the confinement of binary salt systems to the matrix pores can be an effective tool for designing innovative materials with predetermined sorption properties adapted to particular AHT cycles.

Structural phase transitions of barium halide nanocrystals in fluorozirconate glasses studied by Raman spectroscopy

Rare-earth-doped fluorochlorozirconate (FCZ) and fluorobromozirconate (FBZ) glasses developed for fluorescence applications are analyzed, with particular attention paid to their phonon energy spectra. After thermal processing of as-made Eu-doped FCZ and FBZ glasses, Raman measurements show additional phonon bands at low phonon energies, indicating the formation of BaCl2 and BaBr2 nanocrystals, respectively. The phonon bands can be assigned to hexagonal, orthorhombic, or a mixture of both phases of BaCl2 and BaBr2 depending on the annealing conditions. Apart from line broadening, the Raman spectra of the orthorhombic nanocrystals agree well with those of BaCl2 and BaBr2 bulk crystals, while the metastable hexagonal phases of BaCl2 and BaBr2 are investigated only in appropriately treated FCZ and FBZ glasses, respectively. The experimental Raman spectra are compared to first principle studies of the phonon frequencies of the hexagonal and orthorhombic phases of both barium halides, showing good agreement.

Orthoborate Halides with the Formula (M+II)5(BO3)3X: Syntheses, Crystal Structures and Raman Spectra of Eu5(BO3)3Cl and Ba5(BO3)3X (X = Cl, Br)

Single crystals of Eu5(BO3)3Cl were obtained by serendipity by reacting Eu2O3 and Mg with B2O3 at 1300 K in the presence of an NaCl melt for 13 h in silica-jacketed Nb ampoules. Ba5(BO3)3X (X = Cl, Br) crystals were formed by direct synthesis from appropriate amounts of Ba(OH)2, H3BO3 and the respective barium halide (hydrate) in alumina crucibles kept in the open atmosphere at 1300 K for 13 h. The crystal structures of the title compounds were determined with single-crystal X-ray diffraction. All compounds crystallize isotypically to Sr5(BO3)3Cl in the orthorhombic space group C2221 (no. 20, Z = 4) with the lattice parameters a = 1000.34(7), b = 1419.00(9), c = 739.48(5) pm for Eu5(BO3)3Cl, a = 1045.49(5), b = 1487.89(8), c = 787.01(4) pm for Ba5(BO3)3Cl, and a = 1048.76(7), b = 1481.13(9) and c = 801.22(5) pm for Ba5(BO3)3Br. The Raman spectra of all compounds were acquired and are presented and compared to literature data. The incremental volume of the orthoborate (BO3)3− anion has been determined and is compared to the Biltz volume

Raman spectra of barium halides in orthorhombic and hexagonal symmetry: Anab initiostudy

Vibrational properties of bulk crystalline barium halides BaCl${}_{2}$, BaBr${}_{2}$, and BaI${}_{2}$ are theoretically investigated for orthorhombic and hexagonal symmetry with ab initio methods in density functional theory. It is demonstrated that the used method is capable of predicting frequencies of vibrational modes, their symmetry types, and corresponding Raman intensities in reasonable agreement with experimental data for orthorhombic and hexagonal BaCl${}_{2}$ and BaBr${}_{2}$ nanocrystals embedded in fluorozirconate glasses. For orthorhombic BaCl${}_{2}$, a Raman-active phonon mode could be predicted theoretically that was not observed in measurements before.

Sm-activated barium halide nanocrystals in fluorozirconate glasses

Fluorozirconate-based glasses have been doped with samarium and bromine ions.Thermal processing initiates the formation of barium bromide nanocrystals in theglass. Samarium enters the glass matrix either in its divalent or in its trivalentstate. Fluorescence measurements indicate that during the annealing processSm2+ ions enter the nanocrystals leading to enhanced fluorescence efficiency and to changes inthe fluorescence lifetime.

Cerium-doped barium halide scintillators for x-ray and γ-ray detections

Single crystals of Ce-activated BaCl2, BaBr2, and BaI2 were investigated under x-ray and γ-ray excitation. The Ce3+-related x-ray excited luminescence in BaBr2 shifts significantly to longer wavelengths upon increasing the doping level from 0.1% to 1%. In Ce-activated BaCl2 only a slight shift can be observed. BaI2 does not show any Ce3+-related emission. Scintillation decay time measurements show that the decay in BaBr2 is delayed due to migration processes. Additional K doping has a large influence on the scintillation decay time properties but not on the overall efficiency.

Europium-doped barium halide scintillators for x-ray and γ-ray detections

Single crystals of undoped or europium-doped barium chloride, bromide, and iodide were investigated under x-ray and γ-ray excitations. The Eu2+-related x-ray excited luminescence found in the Eu-doped barium halides occurs at 402, 404, and 425nm for the chloride, bromide, and iodide, respectively. BaCl2:Eu2+ shows the best scintillation properties of the systems investigated. The light yield is about 20000±2000photonsperMeV of absorbed γ-ray energy, the energy resolution for the 662keV photopeak is 8.8%±0.9%, and the scintillation decay time is 390±40ns.

Simultaneous measurements of photoelectron and luminescence of barium halides

Photoelectron and optical spectra are both important in order to know the electronic structures of solids, but they have only been measured independently in insulating materials so far. In the present experiments, simultaneous measurements of photoelectron and luminescence spectra of BaF 2 thin films were carried out. It was found that both photoemission and luminescence intensities decrease with increasing synchrotron-radiation doses, indicating the formation of radiation-induced defects. Also, the time correlation between Ba-4d photoelectrons and Auger-free luminescence photons was observed for the first time, suggesting that these two processes correlate with each other.

Hydrothermal Synthesis and Dielectric Properties of Tetragonal BaTiO3

Hydrothermal synthesis of barium titanate (BaTiO{sub 3}) at 240{degrees}C using different barium salts as starting reactants is examined. It is found that halide salts (I{sup {minus}}, Br{sup {minus}}, Cl{sup {minus}}) result in the highest tetragonal content, followed by acetate, nitrate, and hydroxide salts. The tetragonal content was quantified from differential scanning calorimetry by following the endothermic Curie transition around 130{degrees}C and reached as high as 37-39% for the materials made with the barium halides. The particle sizes ranged from 0.15 to 0.37 {mu}m, as estimated by scanning electron microscopy. Sintering and dielectric properties of the barium titanates synthesized from different barium sources were examined. BaTiO{sub 3} made from the chloride salt sintered with high densities at 1250{degrees}C with grain sizes of 1-5 {mu}m and a room-temperature dielectric constant (1 kHz) of 2960. 35 refs., 10 figs., 1 tab.

Solid-state effects on nonradiative decay of 4d94f1 states in barium halides.

The nonradiative decay of 4d 9 4f 1 states in barium halides was investigated by using resonant-photoemission spectroscopy. Constant-final-state spectra with the final state at N 4,5 -O 2,3 O 2,3 Auger electron peak and constant-initial-state (CIS) spectra with the initial state at Ba 5p levels were enhanced in the Ba 4d excitation-energy region, indicating Auger and direct recombination decay processes, respectively