Monoclinic Α-phase Research Articles

Influence of vanadium and dysprosium co-doping on phase stability, microstructure, and electrical properties of Bi2O3

Herein, we report the synthesis of Dy–V co-doped Bi2O3 ceramics using the solid–state processing technique under atmospheric conditions. The X-ray diffraction (XRD) patterns demonstrate the stability of the cubic fluorite δ-Bi2O3 in the V-rich ceramics. However, in Dy-rich ceramics, a mixture of phases, including α and δ, gradually diminishes with increased mutual dopant concentrations, suggesting a transition to the single fcc δ-phase with Fm-3 m space group. According to the Rietveld analysis and electron density representation, it is evident that there are no impure peaks present in α-Bi2O3, which highlights the clear transition to the δ-phase polymorphs. The DTA curves for samples M4 and M7 display a distinct endothermic peak at temperatures around 724.5 and 744.5 °C, indicating a phase transition from the monoclinic α-phase to the cubic δ-phase. These peaks are also attributed to an order-disorder transition (ODT). The FESEM micrographs consistently revealed the existence of irregular and aggregated grains, with an average grain size ranging from 0.80 to 5.57 μm. The level of aggregation became more apparent with the escalation of Dy3+ doping, as opposed to the 5–20 wt% V loading. Moreover, the as-sintered pellets M2 demonstrated the absence of any pore formation compared to other samples, confirming a remarkably high degree of densification. As a result, the as-sintered pellets have a low level of void space, with an apparent porosity of no more than 2.5%. Based on the conductivity measurements and electrochemical impedance spectroscopy (EIS), Bi0.85V0.10Dy0.05O1.5 exhibits the highest electrical conductivity of 0.965 (Ω cm)−1 and an optimal activation energy of 0.537 eV at 627 °C compared to other prepared compositions. This remarkable performance is attributed to the high polarizability and mixed valence cations, especially in V5+-rich ceramics, compared to the Dy3+-rich compositions with a reduced conductivity of 0.010 to 0.097 (Ω cm)−1. The Nyquist plots indicate that impedance decreases with vanadium doping increases until it reaches Bi0.85V0.10Dy0.05O1.5. Higher Dy3+ content increases impedance, leading to lower cell performance. The typical composition can be a solid electrolyte in SOFCs operating at moderate temperatures.

Ex Situ Method for Photoreduction of the Cadmium Ion from Terbium-Loaded Bismuth Vanadium Oxide.

The photoreduction of Cd (II) to Cd (0) was performed using Bi4V2O11, which was tremendously enhanced by Tb3+-doped Bi4V2O11. The relationship between charge carrier isolation and light harvesting was studied in depth in this research, and a promising technique for fabricating effective photocatalysts for heavy metals was discovered. Lattice disorder effects due to size variance between V5+ and Tb3+ cations in Bi4V2O11 nanomaterials substituted with an invariable Tb3+ cation at different concentrations (x = 15, 20, and 25%). Bi4V2O11 and 15% Tb/Bi4V2O11 evidenced a coexistence of monoclinic (α-phase) with a CS/m symmetry, while 25% Tb/Bi4V2O11 was tetragonal (γ-phase) with an I4/mmm symmetry. Raman scattering experiments elucidated the changes in Bi4V2O11 lattice corresponding to oxygen motion, suggesting significant destabilization of the VO4 tetrahedra after addition of Tb3+. The SEM micrograph depicted a disparity in the microstructure with reduced grain size in 25% Tb/Bi4V2O11 samples. However, the TEM micrographs of 25% Tb/Bi4V2O11 nanomaterials revealed that crystallite sizes of 25–35 nm were obtained, presenting a single tetragonal phase, highly homogeneous in nature. Impedance spectroscopy was used to study the conductivity of these compounds in the temperature range of 300 °C. At 300 °C, the compounds with x = 25% showed a conductivity of 15.92 S cm–1. The conductivity values were found to be comparable with the highest values reported in the literature for similar compounds.

CoSO4·H2O and its continuous transition compared to the compression properties of isostructural kieserite-type polymorphs

Abstract The kieserite-type compound cobalt(II) sulfate monohydrate, CoSO4·H2O, has been investigated under isothermal (T = 295 K) hydrostatic compression up to 10.1 GPa in a diamond anvil cell by means of single-crystal X-ray diffraction and Raman spectroscopy. The monoclinic α-phase (space group C2/c) undergoes a second-order ferroelastic phase transition at P c = 2.40(3) GPa to a triclinic β-phase (space group P 1 ‾ $‾{1}$ ). Lattice elasticities derived from fitting third-order Birch-Murnaghan equations of state to the pressure dependent unit-cell volume data yield V 0 = 354.20(6) Å3, K 0 = 53.0(1.7) GPa, K′ = 5.7(1.8) for the α-phase and V 0 = 355.9(8) Å3, K 0 = 45.2(2.6) GPa, K′ = 6.6(6) for the β-phase. Crystal structure data of the high-pressure polymorph were determined at 2.98(6) and 4.88(6) GPa. The most obvious structural feature and thus a possible driving mechanism of the phase transition, is a partial rearrangement in the hydrogen bonding system. However, a comparative analysis of pressure-induced changes in the four kieserite-type compounds investigated to date suggests that the loss of the point symmetry 2 at the otherwise rather rigid SO4 tetrahedron, allowing symmetrically unrestricted tetrahedral rotations and edge tiltings in the β-phase, could be the actual driving mechanism of the phase transition.

Synthesis of C:Se (core:shell) nanoparticles via laser ablation on porous silicon for photodetector application

In this research, C:Se (core:shell) nanoparticles(NPs) are laser ablated at various laser energies of 200, 400, 600, 800 and 1000 mJ with 100shots and 1064 nm laser wavelength then deposited on porous silicon (PS). The XRD study showed that C:Se NPs are crystalline and belong to the monoclinic symmetry α-phase. Results of the AFM (i.e. atomic force microscope) analysis for PS has shown sponge-like structure, and a 39.76 nm average diameter coordinated in a rod-like shape appearing for C:Se NPs, are watched and electrical characteristics are studied to identify samples. From current-voltage (I-V) measures, the electrical characteristics, like height of the barrier (ΦB) and ideality factor (n) of Al/PS/Si/Al and Al/C:Se NPs/PS/Si/Al heterojunction have been determined. Finally, a wide variety of wavelengths has increased the efficacy of C:Se NPs/PS photodetectors.

Study on the structural phase transitions in NaSICON-type compounds using Ag3Sc2(PO4)3 as a model system

NaSICON (Na Super-Ionic CONducting) structured materials are among the most promising solid electrolytes for Li-ion batteries and `beyond Li-ion' batteries (e.g. Na and K) due to their superior ionic conductivities. Although this material has been well known for decades, its exact phase behaviour is still poorly understood. Herein, a starting material of Na3Sc2(PO4)3 single crystals is used, grown by flux methodology, where Na is subsequently chemically replaced by Ag, in order to take advantage of the higher scattering contrast of Ag. It is found that the NaSICON-type compound shows two phase transitions from a low-temperature monoclinic α-phase to a monoclinic β-phase at about 180 K and to a rhombohedral γ-phase at about 290 K. The framework of [Sc2(PO4)3]3− is rigid and does not change significantly with temperature and change of symmetry. The main driving force for the phase transitions is related to order–disorder phenomena of the conducting cations. The sensitivity of the phase behaviour on the ordering of these ions suggests that small compositional changes can have a great impact on the phase behaviour and, hence, on the ionic conductivity of NaSICON-structured materials.

Ab Initio Study of the Effect of Mono-Vacancies on the Metastability of Ga-Stabilized δ-Pu

Most experimental studies on metallic Pu are on the room temperature monoclinic α-phase or the fcc Ga stabilized δ-phase. Stabilized δ-phase Pu-Ga alloys are metastable and exhibit a martensitic phase transformation to α’-phase at low temperatures, or applied shear, with concentrations lower than three atomic percent Ga. By using first principles, we explore the metastability of δ-phase by investigating the structural and electronic behavior induced by Ga alloying and by a mono-vacancy point defect. We find that a site substitutional Ga induces a tetragonal distortion in the lattice affected by hybridization of Ga 4p and Pu 6d states. With the addition of a mono-vacancy, a monoclinic or tetragonal distortion forms locally (dependent on its distance from Ga), and decoupling of the Pu 5f and 6d states and broadening of the 6d states occurs. This response enables hybridization of Pu 6d with the Ga 4p states affecting the mono-vacancy formation energy. Thus, stabilization of the fcc lattice correlates with hybridization of Pu 6d states with Ga 4p states, and this becomes more evident in the presence of a mono-vacancy.

Structure and Properties of Nonwoven Materials Obtained by Electrospinning of a Solution and Melt of Polyamide-6

Nonwoven materials were obtained by electrospinning a solution and melt of polyamide-6; the average fiber diameter during solution spinning was 0.8–4.5 μm, and during melt spinning, 1.5–7.6 μm. It has been established that during electrospinning (both solution and melt) of polyamide-6, a transition occurs from a stable monoclinic α-phase to a metastable pseudohexagonal γ-phase. Annealing of nonwoven fabrics leads to gradual restoration of the original crystal structure of polyamide in materials obtained from the melt, while for materials formed from a solution, changes after annealing are minimal. It has been found that nonwoven fabrics exhibit hydrophobic properties after production, but lose them after being immersed in water. The sorption capacity of the materials for motor oil is 42–81 g/g, and the residual oil content after desorption does not exceed 4 g/g.

Polymorphism of Mg-monohydrate sulfate kieserite under pressure and its occurrence on giant icy jovian satellites

The high-pressure behaviour of hydrated magnesium sulfate kieserite, MgSO4⋅H2O, has been investigated on isothermal compression at T = 295 K up to 8.3 GPa hydrostatic pressure. The crystal properties of synthetic endmember single crystals were investigated using a high-pressure diamond anvil cell by means of in-situ X-ray diffraction and vibrational spectroscopy methods. The experimental study reveals a second-order phase transition from the monoclinic (C2/c) α-phase to a triclinic (P1¯) β-form at a transition pressure of 2.72 GPa. Elastic properties as determined from precise lattice parameters yield static elasticities as described by third-order Birch-Murnaghan equations of state with V0 = 355.5(4) ų, K0 = 48.1(5) GPa, K’ = 8.1(6) for the low-pressure polymorph (α-MgSO4⋅H2O), and V0 = 355.8(1.8) ų, K0 = 49.3(5.5) GPa, K’ = 4.8(1.0) for the high-pressure polymorph (β-MgSO4⋅H2O). The nature of the phase transition and its reversibility on pressure release make it seem unlikely that the β-polymorph can be recovered at surface conditions on any icy satellite, although in the context of impact events it is proposed to exist, but only on a limited time scale before re-transforming to α-MgSO4⋅H2O. With respect to the icy mantles of Ganymede and Callisto, the depth profile of Ganymede following the established thermal gradients suggest a stability field only for α-MgSO4⋅H2O being relevant to the presumable conditions in the icy mantle. In contrast, the depth profile for Callisto, as corresponding to maximum pressures of approximately 5 GPa, crosses the α-to-β-transition boundary and make the high-pressure polymorph a promising candidate rock-forming mineral for the deep icy mantle of the outermost Galilean moon. In particular the material parameters reported for the α and β form of MgSO4⋅H2O are fundamental to compute the icy mantle dynamics and accurately determine the radial density structure in models of Ganymede and Callisto.

Synthesis and Color Evaluation of Ta5+-Doped Bi2O3.

Ta5+-doped Bi2O3 solid solutions, (Bi1–xTax)2O3+2x (0 ≤ x ≤ 0.20), were synthesized by a conventional solid-state reaction method. The crystal structure, optical properties, and color of the pigments were characterized. The (Bi1–xTax)2O3+2x (x = 0, 0.03, 0.04, 0.20) samples were obtained in a single-phase form, and the crystal structure depended on the Ta content; they were monoclinic α-phase (x = 0), tetragonal β-phase (x = 0.03, 0.04), and cubic δ-phase (x = 0.20). Among them, (Bi0.97Ta0.03)2O3.06 strongly absorbed visible light at the wavelength shorter than 480 nm and exhibited the most vivid orange color. The redness value (a*) was comparable to that of commercial orange pigments, and the yellowness value (b*) was slightly larger. Although it is necessary to improve chemical stability, the (Bi0.97Ta0.03)2O3.06 pigment has potential for an environmentally friendly inorganic orange pigment.

Microwave-mediated synthesis, photocatalytic degradation and antibacterial activity of [formula omitted]-Bi2O3 microflowers/novel [formula omitted]-Bi2O3 microspindles

The present article portray the microwave (MW) synthesis of alpha bismuth oxide microflowers (α-Bi2O3 MFs) and novel gamma bismuth oxide microspindles (γ-Bi2O3 MSs) using bismuth nitrate pentahydrate [Bi(NO3)3.5H2O], and polyvinylpyrrolidone (PVP) as a surfactant. The structural, BET surface area, morphological, photocatalytic activity under ultraviolet (UV) light and antibacterial performance was investigated with varying MW irradiation time. XRD study confirmed the formation of monoclinic (α-phase) and body-centered cubic (γ-phase) of Bi2O3 with variation of MW irradiation time for 10 min and 15 min respectively. SEM images revealed the formation of microflowers for α-Bi2O3 and microspindles for γ-Bi2O3. Further HR-TEM illustrated the appearance of nanoflakes (19–35 nm) and the rose-flowers, and back-bending man (15–30 nm) like structures for α-Bi2O3 MFs and γ-Bi2O3 MSs correspondingly. Interestingly, the comparative photocatalytic activity of α-Bi2O3 MFs and γ-Bi2O3 MSs were evaluated under UV-light irradiation for the degradation of five different dyes viz. malachite green (MG), eriochrome black-T (EBT), methyl thymol blue (MTB), bromophenol blue (BPB), and congo-red (CR). The α-Bi2O3 MFs show enhanced photocatalytic activity than γ-Bi2O3 MSs under UV light without decreasing efficiency up to four consecutive cycles and fallows the pseudo-first order reaction kinetics and degradation order: MTB>MG>EBT>CR>BPB. Furthermore, antibacterial assay of α-Bi2O3 MFs and γ-Bi2O3 MSs was carried out against gram-positive (Staphylococcus aureus (S a) and Pseudomonas aeruginosa (P a)) and gram-negative (Escherichia coli (E c), and Klebsiella Pneumonia (K p)) human pathogenic bacteria using agar well diffusion method. The α-Bi2O3 MFs show comparatively better antibacterial activity against P a than γ-Bi2O3 MSs. The current study provides a simple approach to design the α-Bi2O3 MFs and novel γ-Bi2O3 MSs as a photocatalyst for the environmental remediation of organic pollutants (OPs).

Anomalous Temperature Dependence of Isotactic Polypropylene α-on-β Cross-Nucleation Kinetics

A particular kind of heterogeneous nucleation, i.e., cross-nucleation, is sometimes observed in polymorphic substances, when a new crystal structure nucleates on the surface of a crystal of a different modification. Here we show a unique and apparently incongruous nucleation behavior in polymorphic isotactic polypropylene (i-PP). The rate of cross-nucleation of the monoclinic α-phase on the trigonal β-phase crystals increases with increasing temperature, in the vicinity of the α-crystals melting point. This behavior is contrary to that of the heterogeneous nucleation kinetics of the same crystal on various solid substrates, and also to the previously reported cases of cross-nucleation rate of other polymorphic systems, both exhibiting the expected decrease with temperature in the same range of undercoolings. i-PP α-on-β cross-nucleation apparently eludes the nucleation theory. The results are explained as a manifestation of a kinetic competition between α-on-β cross-nucleation and growth of β-crystalline ...

Mechanoluminescence of SrAl2 O4 :Eu,Dy nanophosphors induced by low impact velocity.

The present paper reports the impulsive excitation of mechanoluminescence (ML) in Sr0.97 Al2 O4 :Eu0.01 ,Dy0.02 nanophosphors prepared using a combustion technique. The phosphors are characterized using X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL). The XRD results show that the samples exhibit a monoclinic α-phase in the crystal structure. The space group of SrAl2 O4 :Eu,Dy nanophosphors is monoclinic P21 . The PL and ML spectra of SrAl2 O4 :Eu,Dy nanophosphors are excited using light with a wavelength of 365nm and emission is found at 516nm. The prepared nanophosphors exhibits an intense ML that can be seen in daylight with the naked eye. When a sample powder is deformed impulsively by the impact of a moving piston, the ML intensity initially increases linearly with time, attains a peak value, Im , at time tm , and then decreases with time. The peak ML intensity, Im , and total ML intensity, IT , increase linearly with applied pressure and impact velocity. The ML intensity decreases with successive impacts of load onto the phosphors, and the diminished ML intensity can be approximately recovered by UV irradiation. The activation energy using thermoluminescence is found to be 0.57eV for SrAl2 O4 :Eu,Dy nanophosphors. Copyright © 2016 John Wiley & Sons, Ltd.

Synthesis, phase stability and oxide ion conductivity of Ce(IV)–Cd(II) double substituted bismuth vanadate

Bi4V2O11-δ has been doped with Ce and Cd to study double substitution. The system with various dopant concentrations (0.07 ≤ x ≤ 0.30) was prepared by the standard solid-state reaction method. The correlation between the polymorphism and oxide ion performance was well investigated as a function of temperature and composition with the help of thermal analysis, X-ray diffraction (XRD) and AC impedance spectroscopy. From XRD results it is seen that the high oxide ion conducting tetragonal γ-phase is stabilized for x = 0.17. For the compositions x ≤ 0.10, monoclinic α-phase is retained at room temperature with clear evidence for two successive phase transitions α ↔ β and β ↔ γ. For x = 0.13, β ↔ γ phase transition is seen. However, the existence of order–disorder, γ' ↔ γ transition was confirmed for x = 0.17. It is seen that the highest low-temperature ionic conductivity at 320 °C is 3.19 × 10−4 S cm−1 which was observed for x = 0.17.

X-Ray Diffraction Study of Oxygen-Conducting Compounds Ln2Mo2O9(Ln = La, Pr)

Lanthanum molibdate La2Mo2O9(LM) and the compounds on its basis (LAMOX) attract much attention because of the high oxygen conductivity (6x10-2Sm/cm), which were found by Lacorre group. LM has the first-order phase transition at about 5800C and two phases: low-temperature monoclinic α-phase (P21) and high-temperature β-phase (P213) [1]. In the present work single crystals Ln2Mo2O9(Ln = La, Pr) were obtained by spontaneous flux crystallization in the Ln2O3–MoO3oxide systems. The LM and PM single crystals are studied by precision X-ray diffraction and high-resolution transmission microscopy. A cubic cell with a = 7.155(1) and 7.155(1) Å was chosen for two LM samples (LM_I and LM_II, respectively). More than 90% (LM_I) and 60% (LM_II) of the reflections measured were indexed in this cell. The unit cell parameter of the PM compound is slightly shorter: a = 7.087(1) and 7.089(1) Å for the PM_I and PM_II samples, respectively. More than 90% of the reflections measured were indexed for both PM crystals. It was found that the LM_II crystal consists of two cubic components grown together; a ≍ 7.155 Å for both components. The crystal structures for two LM and two PM samples are determined in space group P213. It is found that La and Pr atoms, as well as Mo1 and O1 atoms, are located in the vicinity of 3-fold axes rather than on the axes like in the high-temperature cubic phase. In both structures, the O2 and O3 positions are partially occupied. The coexistence of different configurations of the Mo coordination environment facilitates the oxygen ion migration in the structure. Based on the X-ray data, activation energies of oxygen atoms are calculated and migration paths of oxygen ions in the structures are analyzed. The conductivity of PM crystals is close to that of LM crystals. Oxygen atoms O2 and O3 make main contributions to ion conductivity of LM and PM. This study was supported in part by part by the Russian Foundation for Basic Research (project no. 14-02-00531).

Solid state transitions of Bi2O3nanoparticles

Abstract

Solid phases of spatially nanoconfined oxygen: A neutron scattering study

We present a comprehensive neutron scattering study on solid oxygen spatially confined in 12 nm wide alumina nanochannels. Elastic scattering experiments reveal a structural phase sequence known from bulk oxygen. With decreasing temperature cubic γ-, orthorhombic β- and monoclinic α-phases are unambiguously identified in confinement. Weak antiferromagnetic ordering is observed in the confined monoclinic α-phase. Rocking scans reveal that oxygen nanocrystals inside the tubular channels do not form an isotropic powder. Rather, they exhibit preferred orientations depending on thermal history and the very mechanisms, which guide the structural transitions.

Synthesis of α-Bi4V2O11 and its Sonocatalytic Activity for the Degradation of Rhodamine B

A simple method for preparing highly sonoactive nano-sized bismuth vanadate (α-Bi4V2O11) was prepared by combustion technique. The prepared α- Bi4V2O11 powders were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). High-resolution TEM images displayed well defined Braggs planes having interplaner distances (dhkl) 3.04A and 3.12A, which were in good agreement with the (025) at 2θ = 30.56 o and (133) at 2θ = 28.04 o planes observed in the XRD pattern of monoclinic α-phase of bismuth vanadate respectively. The ultrasonic degradation of Rhodamine B (Rh B) was studied in the absence of catalyst and in the presence of catalyst. The rate of degradation of catalyzed reaction was higher than that obtained with in the absence of the catalysts. The observed pseudo-first-order rate constant increased from 0.010 min -1 to 0.017 min -1 as the concentration of catalyst Rh B increased from 0.03 mg/ml to 0.33 mg/ml. The possible reaction mechanism of sonocatalytic degradation of Rh B over α-Bi4V2O11 has also been discussed. Thus, in this paper we have concluded that bismuth vanadate is a stable and efficient catalyst for the industrial waste-water treatment.

Impact of Film Structure on Ionization Energy of Titanyl-Phthalocyanine in Thin Films

ABSTRACTStructure-related ionization energy (IE) of vacuum-deposited titanyl-phthalocyanine (OTiPc) thin films was investigated by using in situ ultraviolet photoelectron spectroscopy (UPS) and X-ray diffractometry. Distinct molecular orientations (i.e. lying-flat and standing-up orientation) in different polymorphous (i.e. monoclinic β-phase and triclinic α-phase) were observed on a surface of polycrystalline (poly-) Au and octadecyltrichlorosilane-self assembled monolayer (OTS-SAM). For the two structures IE of the highest occupied molecular orbital (HOMO) of OTiPc thin films altered significantly by 0.55 eV. The different IE was attributed to surface dipole potential and strong intermolecular interaction.

The generalized embedded atom model of interatomic interaction and its application to α-Pu

The generalized embedded-atom model (GEAM) for interatomic interaction in metals with complex electronic and crystal structure has been developed as a modification of the angular dependence term of well-known MEAM potential. Here we present an analytical form of the new interatomic potential, including partial forces ready to be implemented into MD computer code. The new model has been applied to low-temperature monoclinic α-phase of plutonium. In rather long MD simulations with flexible unit cell geometry it has been shown that monoclinic lattice proved to be mechanically stable in temperature range 0–300K and at zero stress tensor. Results of MD simulations obtained with the new model at finite temperatures were compared with experimental and ab initio data on the properties of the material.

Luminescence and Raman study of α-Bi2O3 ceramics

Cathodoluminescence in the scanning electron microscope and photoluminescence in a confocal microscope have been used to investigate the luminescence properties of the stable monoclinic α-phase of Bi2O3. Powders of this oxide have been sintered at temperatures of 500°C and 750°C in air or in nitrogen atmospheres. Spectra of the starting powder and of the samples treated at 500°C show luminescence bands at 1.50eV and 1.95eV as well as a band at 2.1eV, more prominent in nitrogen treated samples. Sintering at 750°C leads to quenching of the 1.50eV infrared emission and the formation of a broad band with emission above 3eV. The evolution of Raman bands with the sintering treatments has also been investigated.