Increasing Barium Content Research Articles

X-ray luminescence of Sr0.925–xBaxEu0.075F2.075 nanopowders

We synthesized powders of single-phase solid solutions Sr0.925–xBaxEu0.075F2.075 (x = 0.00, 0.20, 0.25, 0.30, 0.35 and 0.40) by a precipitation technique from nitrate aqueous solutions. The lattice parameters increase linearly as the barium content increases. We recorded a significant increase in the X-ray luminescence intensity of europium at increasing barium content. Upon increasing barium content, the intensity of the luminescence of strong 5D0 → 7F1 band increases exponentially, and we observed blue and red shifts in the position of the europium luminescence bands for 5D0 → 7F1 and 5D0 → 7F4, respectively

Effects of a barium-based additive on gaseous and particulate emissions of a diesel engine

The addition of barium-based additives is one of the main methods used to suppress smoke emissions in non-road diesel engines. Herein, a commercial barium-based additive was added to diesel fuel at the manufacturer's recommended concentration and used in a non-road four-cylinder supercharged diesel engine, without an after-treatment system, in bench experiments. Regulated emissions of the diesel engine were measured, volatile organic compounds (VOCs) and particulate matter (PM) were sampled. The carbonaceous fraction, water-soluble ions and inorganic elements in the PM were analyzed. Results indicated that the additive effectively reduced carbon monoxide (CO), hydrocarbon (HC) and smoke emissions from the engine. A 71% reduction in smoke was observed at the rated working condition, which was the maximum reduction of the three tested conditions. The additive produced a 36% reduction of VOCs at the rated working condition. The proportion of high carbon number hydrocarbons in the VOCs increased while the atmospheric reactivity of the VOCs decreased. The additive suppressed the concentration of organic carbon (OC) and elemental carbon (EC) emissions with a maximum reduction (40%) of total carbon achieved under the rated working condition. After the application of the additive, the concentration of water-soluble ions (Cl-, SO42‐, NO3‐, Na+, K+, Ca2+, NH4+) and elements (Fe, Mn, S, Ca, Ba) in the PM increased. A trend of increasing Barium content in the PM matched a similar trend of decreasing smoke.

Dynamic Barriers to Crystallization of Calcium Barium Carbonates

Metastable carbonates play important roles in geochemistry, biomineralization and serve as model systems for nonclassical theories of nucleation and growth. Balcite (Ca0.5Ba0.5CO3) is a remarkable carbonate phase that is isostructural with a high-temperature modification of calcite (CaCO3), yet can be synthesized at ambient conditions. Here, we investigate crystallization pathways in the Ba–Ca–CO3–H2O system, with a focus on the transformation of amorphous calcium barium carbonate (ACBC) to balcite and subsequent decomposition into the equilibrium calcite (CaCO3) and witherite (BaCO3) phases. Density functional theory calculations show that balcite is an unstable solid solution (Ca1–xBaxCO3, R3̅m) in the range 0.17 < x < 0.5, but is accessible through the amorphous ACBC precursor for x ≲ 0.5, and predict its decomposition into calcite and witherite. We confirm this pathway experimentally but found demixing to proceed slowly and remain incomplete even after 9 months. Nucleation kinetics of balcite from ACBC was assessed using a microfluidic assay, where increasing barium content led to a surprising increase in the balcite nucleation rate, despite decreasing thermodynamic driving force. We attribute crystallization rates that dramatically accelerate with time to changes in interfacial structure and composition during coarsening of the amorphous precipitate. By carefully quantifying the thermodynamic and kinetic contributions in the multistep crystallization of a metastable carbonate, we produce insights that allow us to better interpret the formation and persistence of metastable minerals in natural and synthetic environments.

Structural Basis for Metastability in Amorphous Calcium Barium Carbonate (ACBC)

AbstractMetastable amorphous precursors are emerging as valuable intermediates for the synthesis of materials with compositions and structures far from equilibrium. Recently, it was found that amorphous calcium barium carbonate (ACBC) can be converted into highly barium‐substituted “balcite,” a metastable high temperature modification of calcite with exceptional hardness. A systematic analysis ACBC (Ca1‐xBaxCO3·1.2H2O) in the range from x = 0–0.5 is presented. Combining techniques that independently probe the local environment from the perspective of calcium, barium, and carbonate ions, with total X‐ray scattering and a new molecular dynamics/density functional theory simulations approach, provides a holistic picture of ACBC structure as a function of composition. With increasing barium content, ACBC becomes more ordered at short and medium range, and increasingly similar to crystalline balcite, without developing long‐range order. This is not accompanied by a change in the water content and does not carry a significant energy penalty, but is associated with differences in cation coordination resulting from changing carbonate anion orientation. Therefore, the local order imprinted in ACBC may increasingly lower the kinetic barrier to subsequent transformations as it becomes more pronounced. This pathway offers clues to the design of metastable materials by tuning coordination numbers in the amorphous solid state.

The impact of Ba substitution on high-temperature transport in lanthanum-strontium ferrite

Effect of barium content on structural, thermal, and transport properties of oxides La0.49Sr0.5–x Ba x FeO3–δ (х = 0, 0.25, 0.50) was studied with the emphasis on their potential use for electrodes and oxygen transport membranes. Barium substitution for strontium was found to enhance symmetry of crystalline lattice, facilitate the oxygen release on heating, and favor the increasing thermal expansion of La0.49Sr0.5–x Ba x FeO3–δ . Analysis of electrical conductivity depending on the partial oxygen pressure allowed to separate the contributions of oxygen ions, electrons, and holes in high-temperature electrical transport in order to trace barium effect on conductivity components. Electron conductivity of n-type and its activation energy does not reveal sensitivity to barium concentration in oxides. Oxygen ion conductivity is shown to decrease with increasing barium content in La0.49Sr0.5–x Ba x FeO3–δ while respective activation energy increases from 0.70 to 0.79 eV. About four times decrease of p-type electron conductivity at invariable activation energy was detected as a result of the substitution degree increase from x = 0 to x = 0.5. Possible mechanisms of barium influence on properties of oxides are discussed.

Effect of barium content on dielectric and energy storage properties of (Pb,La,Ba)(Zr,Sn,Ti)O3 ceramics

The effect of barium content on phase development, dielectric property and energy storage performance of (Pb0.925−xLa0.05Bax) (Zr0.52Sn0.39Ti0.09)O3 (PLBZST) ceramics synthesized by a solid state reaction method was investigated. X-ray diffraction patterns and scanning electron microscopy micrographs illustrated that the pyrochlore phase was effectively suppressed by the introduction of barium in the (Pb0.925La0.05) (Zr0.52Sn0.39Ti0.09)O3 (PLZST) ceramics. The increase in maximum dielectric constant and the decrease in both transition temperature and switching field with increasing barium content were due to the decrease in the stability of antiferroelectric phase. The energy storage performance of the barium doped PLZST ceramics was studied by measurements of polarization hysteresis loops and discharge curves. The increase of barium content led to the increase of the energy storage density at first and then slight decrease. The study of cyclic charge–discharge showed that barium doped PLZST ceramic capacitor can withstand up to 10,000 cycles with about 8% energy density loss.

An investigation on the microstructures and magnetic properties of the Sr0.35−xBaxCa0.30La0.35Fe11.71Co0.29O19 hexaferrites

M-type hexaferrite Sr0.35−xBaxCa0.30La0.35Fe11.71Co0.29O19 (0≤x≤0.35) magnetic powders and magnets were prepared by the solid-state reaction. The phase compositions of the magnetic powders were investigated by X-ray diffraction. X-ray diffraction patterns show that the hexagonal single phase is obtained in all samples. The micrographs of the magnets were observed by a field emission scanning electron microscopy. All magnets have formed hexagonal structures and the particles are distributed evenly. Magnetic properties of the magnets were measured by a magnetic properties test instrument. The remanence, intrinsic coercivity, magnetic induction coercivity and maximum energy product of the magnets continuously decrease with increasing barium content (x).

Effects of barium content on microstructure and magnetic properties of Sr0·7−xBaxLa0·3Fe11·8Zn0·2O19 M type hexaferrites

M type hexaferrite Sr0·7−xBaxLa0·3Fe11·8Zn0·2O19 (0≤x≤0·7) magnetic powders and magnets were prepared by the ceramic process. X-ray diffraction was used to investigate phase compositions of the magnetic powders. X-ray diffraction patterns show that the hexagonal single phase is obtained in all samples. A field emission scanning electron microscopy was employed to examine the micrographs of the magnets. All magnets have formed hexagonal structures, and the particles are distributed homogeneously. Magnetic properties of the magnets were measured by a magnetic properties test instrument. The remanence, intrinsic coercivity, magnetic induction coercivity and maximum energy product of the magnets continuously decrease with increasing barium content x.

Ionic conduction in Ba xCe 0.8Pr 0.2O 3–α

Ba x Ce 0.8Pr 0.2O 3– α ( x=0.98–1.03) ceramics were prepared by high temperature solid-state reaction. X-ray diffraction (XRD) patterns showed that the materials were perovskite-type orthorhombic single phase. By using gas concentration cell and AC impedance spectroscopy methods, the electrical conduction behavior of the materials was investigated in different gases at 500–900 °C. The influence of nonstoichiometry in the materials with x≠1 on conduction properties was studied and compared with that in the material with x=1. The results indicated that Ba 1.03Ce 0.8Pr 0.2O 3– α was a pure protonic conductor, and Ba 0.98Ce 0.8Pr 0.2O 3– α was a mixed conductor of protons and electrons in wet hydrogen at 500–900 °C. BaCe 0.8Pr 0.2O 3– α was a pure protonic conductor in 500–600 °C, and a mixed conductor of protons and electrons above 600 °C in wet hydrogen. In 500–900 °C, they were all mixed conductors of oxide ions and electronic holes in dry air, and mixed conductors of protons, oxide ions and electronic holes in wet air. Both the protonic and oxide ionic conductivities increased with increasing barium content in the materials in wet hydrogen, dry air and wet air, respectively.

Reducing the positional modulation of NbO6-octahedra in Sr x Ba1–x Nb2O6 by increasing the barium content: A single crystal neutron diffraction study at ambient temperature for x = 0.61 and x = 0.34

Abstract We report on the influence of the barium content on the modulation amplitude in Sr x Ba1–x Nb2O6 compounds by comparing Sr0.61Ba0.39Nb2O6 (SBN61) and Sr0.34Ba0.66Nb2O6 (SBN34). Our single crystal neutron diffraction results demonstrate that the amplitude of the positional modulation of the NbO6 octahedra is reduced with increasing barium content, indicating that the origin of the modulation is the partial occupation of the pentagonal channels by Sr and Ba atoms. By increasing the Sr content the bigger Ba atoms are replaced by the smaller Sr atoms, which leads to a larger deformation of the surrounding lattice and hence to a larger modulation amplitude. The more homogeneous the filling of these channels with one atomic type (Ba) the lower the modulation amplitude. Our results also show that the structure can be described with a two-dimensional incommensurate harmonic modulation. No second order modulation has been observed, both by single crystal diffraction measurements and q-scans. The positional modulation of the Nb atoms is much smaller than that of the oxygen atoms, such that the modulation can be seen as a rotational modulation of almost rigid NbO6-octahedra.

Effect of barium on diffusion of sodium in borosilicate glass

Diffusion coefficients of sodium in barium borosilicate glasses having varying concentration of barium were determined by heterogeneous isotopic exchange method using 24Na as the radiotracer for sodium. The measurements were carried out at various temperatures (748–798 K) to obtain the activation energy ( E a) of diffusion. The E a values were found to increase with increasing barium content of the glass, indicating that introduction of barium in the borosilicate glass hinders the diffusion of alkali metal ions from the glass matrix. The results have been explained in terms of the electrostatic and structural factors, with the increasing barium concentration resulting in population of low energy sites by Na + ions and, plausibly, formation of more tight glass network. The leach rate measurements on the glass samples show similar trend.

Structural Characterization of Pb1−xBaxZr0.65Ti0.35O3 Ferroelectric Ceramics

In this work, X-ray absorption near edge structure (XANES) and X-Ray Diffraction (XRD) have been used to characterize, respectively, the short and long range-order structure of Pb1− xBaxZr0.65Ti0.35O3 ceramics for 0.0 ≤ x ≤ 0.40. According to XRD-Rietveld refinements, a gradual rhombohedral to cubic like-phase transition occurs with increasing barium content. It is verified that the rhombohedral structural model fits well with the lower barium-content samples, while for the highest barium-content sample (x = 0.40) the fitting parameters obtained for the cubic phase is significantly better. The XANES measurements indicated that the local structure around Ti remains distorted for all barium concentrations, thus suggesting that the local structure of PBZT is weakly dependent on the crystallographic phase.

Ionic conduction in Ba xCe 0.8Er 0.2O 3− α

Ba x Ce 0.8Er 0.2O 3− α ( x=0.98–1.03) solid electrolytes were synthesized by high temperature solid-state reaction. X-ray diffraction (XRD) patterns showed that the specimens were a single perovskite-type orthorhombic phase. The conduction properties of the specimens were studied electrochemically in the temperature range of 600–1000 °C. The influence of nonstoichiometry in the specimens with x≠1 on conduction properties was investigated and compared with that in the specimen with x=1. These three specimens showed a good protonic conduction under wet hydrogen, a mixed conduction of oxide-ion and electronic hole under dry higher oxygen partial pressure, and a mixed conduction of proton, oxide-ion and electronic hole under wet higher oxygen partial pressure. Both of the protonic and oxide-ionic conductivities increased with increasing barium content in the specimens under wet hydrogen and dry air, respectively.

Structural and microwave dielectric properties of Sr1-xBaxNb2O6ceramics at microwave frequencies

Microwave dielectric properties and crystal structure of Sr1-xBaxNb2O6 ceramics (x = 0·39, 0·45, 0·50, 0·55, 0·57, 0·60, 0·65) have been investigated. The microwave cavity perturbation technique was employed for the study of dielectric properties. Parameters such as complex permittivity and conductivity of strontium barium niobate ceramics were determined at the S band by measuring changes in the resonant frequencies and Q values of the cavity resulting from the introduction of the sample. The real part of the complex permittivity of all samples shows an increase with frequency, whereas the imaginary part of permittivity decreases as frequency increases. The effects of composition and sintering temperature on crystal structure and microstructure were studied by X-ray powder diffraction and scanning electron microscopy. Most compositions show preferred orientations along the c axis, as is evident from the relatively high intensity of (001) and (002) peaks. The microstructure contains ferroelectric domainlike structures with increasing barium content.

The reaction of nitrogen with dilute solutions of barium in liquid lithium: electrical resistivity, X-ray phase analysis, kinetic and thermal analysis studies

The reaction of nitrogen with liquid lithium containing dissolved barium which follows a solution–precipitation mechanism has been studied. Initially, nitrogen dissolves in the liquid metal to form an homogeneous solution; the reaction is first order with respect to nitrogen with an activation energy of 33.6 kJ mol–1. Subsequently, it reacts to form a precipitate of Li3N; the Li3N crystallisation face is dependent on the barium content of the solution, nitrogen solubility rising with increasing barium content. The ternary nitride, LiBaN, is only formed on cooling the solution; there is no evidence for Ba2N or Ba3N2 formation. This behaviour contrasts with that in the corresponding Na–M–N (M = Sr or Ba) systems where the solubility is directly proportional to the alkaline-earth metal content of the solution and the precipitating phase is the alkaline-earth metal subnitride. M2N (M = Sr or Ba). Analysis of the crystallisation fields of Li, Li4Ba, LiBaN and Li3N indicated they are separated by monovariant curves which fall from the binary eutectics (Li–Ba, xBa= 0.105 and 416 K; Li–N. degenerate at 453.5 K, Li3N–LiBaN, unknown) through a quasi-peritectic equilibrium involving liquid, lithium, Li4Ba and LiBaN (372 K) to a ternary eutectic point based on liquid, lithium. Li3N and LiBaN (368 K).

Ferroelectricity in the system Pb (1− x) Ba x(Mg [formula omitted])O 3

A series of ceramics of composition Pb (1− x) Ba x (Mg 1 3 Nb 2 3 )O 3 has been prepared, with x varying in regular intervals between 0 and 1. The mixed oxide processing route to lead barium magnesium niobate (PBMN) powders involves the preparation of magnesium niobate, MgNb 2O 6, as an intermediate compound, in order to inhibit the formation of pyrochlore phase. All samples in the composition range are sintered by conventional methods, except the x = 1 composition, for which fast firing is used. The weak-field dielectric response has been measured for each composition, and the results interpreted in terms of the variation in chemical composition between the samples. The niobium-oxygen coordination polyhedra are considered to be the basic polar units, and the function of the Pb 2+ ions is to couple the individual niobium-oxygen octahedra together to form a ferroelectric network. The effect of the Ba 2+ ion is to weaken this coupling. The ferroelectric response of each composition is thought to be due to lead-rich microregions, which become progressively smaller as the relative barium content is increased. The rate of fall-off of relative permittivity with increasing barium content suggests that lead-rich ferroelectric clusters of ions persist to high values of x. An assessment is made of the contribution of this work to the development of structure-dielectric property relationships in relaxor ferroelectrics.