Search Results (8)

In this study, the luminescence efficiency of a crystal-form barium fluoride (BaF₂) inorganic scintillator was assessed for medical imaging applications. For the experiments, we used a typical medical X-ray tube (50–140 kVp) for estimating the absolute luminescence efficiency (AE). Furthermore, we examined the spectral matching of the inorganic scintillator with a series of optical detectors. BaF₂ showed a higher AE than cerium fluoride (CeF₃), comparable to that of commercially available bismuth germanate (Bi₄Ge₃O₁₂-BGO), but lower than that of the gadolinium orthosilicate (Gd₂SiO₅:Ce-GSO:Ce) inorganic scintillator. The maximum AE of BaF₂ was 2.36 efficiency units (EU is the S.I. equivalent μWm⁻²/(mR/s) at 140 kVp, which is higher than that of the corresponding fluoride-based CeF₃ (0.8334 EU)) at the same X-ray energy. GSO:Ce and BGO crystals, which are often integrated in commercial positron emission tomography (PET) scanners, had AE values of 7.76 and 3.41, respectively. The emission maximum (~310 nm) of BaF₂ is adequate for coupling with flat-panel position-sensitive (PS) photomultipliers (PMTs) and various photocathodes. The luminescence efficiency results of BaF₂ were comparable to those of BGO; thus, it could possibly be used in medical imaging modalities, considering its significantly lower cost. Full article

We present structural, morphological, optical and photocatalytic properties of multiferroic Bi_0.98Ba_0.02FeO₃ (BBFO2) perovskite thin films prepared by a combined sol–gel and spin-coating method. X-ray diffraction (XRD) analysis revealed that all the perovskite films consisted of the stable polycrystalline rhombohedral phase structure (space group R3c) with a tolerance factor of 0.892. By using Rietveld refinement of diffractogram XRD data, crystallographic parameters, such as bond angle, bond length, atom position, unit cell parameters, and electron density measurements were computed. Scanning electron microscopy (SEM) allowed us to assess the homogeneous and smooth surface morphology of the films with a small degree of porosity, while chemical surface composition characterization by X-ray photoelectron spectroscopy (XPS) showed the presence of Bi, Fe, O and the doping element Ba. Absorption measurements allowed us to determine the energy band gap of the films, while photoluminescence measurements have shown the presence of oxygen vacancies, which are responsible for the enhanced photocatalytic activity of the material. Photocatalytic degradation experiments of Methylene Blue (MB), Methyl orange (MO), orange G (OG), Violet and Rhodamine B (RhB) performed on top of BBFO2 thin films under solar light showed the degradation of all pollutants in varying discoloration efficiencies, ranging from 81% (RhB) to 54% (OG), 53% (Violet), 47% (MO) and 43% (MB). Full article

The problem of industrial dyes depollution has pushed the scientific research community to identify novel photocatalysts with high performance. Herein, new photocatalysts composed of BaTiO₃, BaTi_0.96Cu_0.04O₃, BaTi_0.96Cu_0.02V_0.02O₃ and BaTi_0.96Cu_0.02Nb_0.02O₃ powders were prepared by solid-state reaction. The structural analysis of the samples confirmed the formation of the BaTiO₃ structure. The splitting of (002) and (200) planes verified the formation of the tetragonal phase. The XRD peaks shifted, and the unit cell volume expansion verified the substitution of the Ti⁴⁺ site by Cu²⁺, V⁴⁺ and Nb⁵⁺ ions. The morphological measurements showed that the addition of (Cu, V) and (Cu, Nb) ions changes the particles’ morphology of BaTiO₃, reducing its grains size. After the incorporation of (Cu, V) and (Cu, Nb) ions, the band gap of BaTiO₃ was reduced from 3.2 to 2.84 and 2.72 eV, respectively. The modification of BaTiO₃ by (Cu, Nb) ions induced superior photocatalytic properties for methyl green and methyl orange with degradation efficiencies of 97% and 94% during 60 and 90 min under sunlight irradiation, respectively. The total organic carbon results indicated that the BaTi_0.96Cu_0.02Nb_0.02O₃ catalyst has a high mineralization efficiency. In addition, it possesses a high stability during three cycles. The high photodegradation efficiency of Bi_0.96La_0.02Gd_0.02FeO₃ was related to the wide-ranging visible light absorption. Full article

BaPb_1−xBi_xO₃ (BPBO) bismuthate, showing high T_C superconductivity for 0.05 < x < 0.35, is an archetypal system for studying the complex inhomogeneity of perovskite lattice favoring the emergence of quantum coherence, called the superstripes phase. Local lattice fluctuations, detected by EXAFS; nanoscale stripes, detected by electron microscopy; and two competing crystalline structures, detected by diffraction, are known to characterize the superconducting phase. At nanoscale [BaBiO₃] centered nanoscale units (BBO) coexist with BaPbO₃ centered (BPO) units in the BPBO perovskite; therefore, we expect a tensile microstrain in BPO units due the misfit strain between the two different lattices. Here, we report the measurement of the spatial micro-fluctuations of the local tensile microstrain ε in the BaPO units in superconducting Ba(Pb_1−xBi_x)O₃ crystals with x₁ = 0.19 an x₂ = 0.28. We show here the feasibility of applying the scanning dispersive micro-X-ray absorption near edge structure (SdμXANES) technique, using focused synchrotron radiation, to probe the microscale spatial fluctuations of the microstrain in BPO units. This unconventional real-space SdμXANES microscopy at the Pb L₃ edge has been collected in the dispersive mode. Our experimental method allows us to measure either the local Bi chemical concentration x and the local lattice microstrain of local BBO and BPO units. The 5 × 5 micron-size spots from the focused X-ray beam allowed us to obtain maps of 1600 points covering an area of 200 × 200 microns. The mapping shows a substantial difference between the spatial fluctuations of the microstrain ε and the chemical inhomogeneity x. Moreover, we show the different relations ε(x) in samples with lower (x₁ = 0.19) and higher (x₂ = 0.28) doping respect to the optimum doping (x = 0.25). Full article

Relaxor-type ferroelectrics show important potential in energy storage fields due to their significantly enhanced energy performance and good temperature stability compared to normal ferroelectrics. Here, a novel, high-performance ternary composition, (0.4−x)BiFeO₃-xBi(Mg_1/2Ti_1/2)O₃–0.6BaTiO₃ (x = 0.2, 0.25, 0.3, 0.35, 0.4), was designed by compositional modulation, which displays typical relaxor characteristics. The optimum energy storage properties can be attained at x = 0.35, accompanied by energy efficiency of 84.87%, a promising energy storage density of 2.3 J/cm³ and good temperature stability of less than 10% over 20–160 °C. Moreover, the samples provide stable cycling fatigue after 10⁵ cycles and a fast discharge time of t_0.9 < 0.1 μs, indicative of promising applications in energy units. Full article

Bismuth based quaternary glasses with compositions BiBLM: 50Bi₂O₃–20B₂O₃–15Li₂O–15MO (where MO = ZnO, CdO, BaO, and PbO) were processed by conventional melt quenching. The effectiveness of various modifier oxides on the optical and structural properties of the developed glasses was studied systematically by XRD, DSC, FTIR, Raman, and optical absorption (OA) measurements. The synthesized glass specimens were characterized by XRD and the patterns demonstrated an amorphous nature. The physical characteristics such as molar mass, density, and OPD values were found to increase with an increase in the molar mass of the modifier oxides, while there was a decrement in oxygen molar volume, thus resulting in decrement of complete molar volume of the prepared glasses. From DSC analysis, incorrigible reduction and enhancement of T_g and thermal stability among various modifier oxides in the glass network was noticed. Optical absorption data for glass specimens have confirmed the decrease in both direct and indirect optical band gap values among various modifier oxides incorporation. These investigations support the obtained Urbach energy (UE) and metallization criteria of synthesized glasses. The ionic characteristic for the glass specimens were confirmed by the values of electronic polarizability and electronegativity. The Raman and FT-IR spectra of the glass specimens displayed the existence of BiO₃, BiO₆, ZnO₄, CdO₄, BaO₄, BO₃, PbO₄, and BO₄ structural units within the glass matrix. These structural results can support the applications of as-developed glasses in the area of photonics. Full article

The synthesis of non-lead piezoelectric ceramics (1–z)(0.65Bi_1.05Fe₂O₃-0.35BaTiO₃)-z Ba(Ti_0.8Zr_0.2)O₃-(Ba_0.7Ca_0.3)TiO₃ using a solid state method and a quenching strategy was investigated. The processing conditions such as the sintering temperature and soaking time were optimized. The patterns of X-ray diffraction (XRD) displayed a pure perovskite structure with no secondary phases. The ferroelectric and piezoelectric characteristics of the samples were considerably improved as a result of the lattice strain. The findings of the experiment revealed that the quenching technique increases the piezoelectric sensor constant of 152 pC/N in optimized conditions. The enhanced piezoelectric sensor constant (d₃₃) value at z = 0.020 was ascribed to the incorporation of multi-cationic BCZT, which modified the bond lengths at a unit cell level and gave rise to more flexibility in complex domain switching. This facilitated easier domain alignment in response to the applied field and resulted in an improvement in the electrical properties. Full article

Superlattice-structured epitaxial thin films composed of Mn(5%)-doped BiFeO₃ and BaTiO₃ with a total thickness of 600 perovskite (ABO₃) unit cells were grown on single-crystal SrTiO₃ substrates by pulsed laser deposition, and their polarization and dielectric properties were investigated. When the layers of Mn-BiFeO₃ and BaTiO₃ have over 25 ABO₃ unit cells (N), the superlattice can be regarded as a simple series connection of their individual capacitors. The superlattices with an N of 5 or less behave as a unified ferroelectric, where the BaTiO₃ and Mn-BiFeO₃ layers are structurally and electronically coupled. Density functional theory calculations can explain the behavior of spontaneous polarization for the superlattices in this thin regime. We propose that a superlattice formation comprising two types of perovskite layers with different crystal symmetries opens a path to novel ferroelectrics that cannot be obtained in a solid solution system. Full article