Structural and microstructural evolution due to increasing Co substitution in Ni1−xCoxFe2O4: An X-ray diffraction study using the Rietveld method

X-ray diffraction studies employing the Rietveld analysis is reported on the influence of increasing Co substitution on the structural and microstructural evolution in AB₂O₄ type spinel ferrites: Ni_1−xCo_xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0). The specimens were synthesized by the organic precursor method. Structure refinement reveals that the pure NiFe₂O₄ is not an exact inverse spinel and about 11% of Ni²⁺ ions occupy the tetrahedral (A) sites. Increasing Co concentrations had the effect of increasing the ratio of B[Fe3+]/A[Fe3+]${[\text{F}{\text{e}}^{3+}]}^{\text{B}}/{[\text{F}{\text{e}}^{3+}]}^{\text{A}}$ and gradual expansion of the ferrite unit cell. The microstructure refinement estimates that the particle size values are in the order of ∼nm, ranging from 31 to 61 nm, which gradually increase with increasing Co doping accompanied by almost negligible lattice micro strains (∼10⁻⁴). The corresponding particle size distribution for each specimen was obtained from the X-ray diffraction data from the basic assumption that the spherical nanoparticles follow the log-normal distribution. The size distribution for the pure NiFe₂O₄ was also estimated from transmission electron microscope and agreed well with that obtained by the diffraction data analysis.     

Influence of chemical composition on the damping characteristics of Cu–Al–Ni shape memory alloys

Cu–XAl–4Ni shape memory alloys (SMAs) are capable of martensitic transformation across a wide temperature range through the precise adjustment of their chemical composition from X = 13.0 to 14.5. In addition, the variations in chemical composition significantly influence the internal friction characteristics of Cu–XAl–4Ni SMAs. Cu–XAl–4Ni SMAs with a higher content of Al exhibit lower internal friction peaks due to decreases in the amount of transformed martensite and the formation of γ₂ phase precipitates. The damping capacity of the inherent and intrinsic internal friction for Cu–13.5Al–4Ni SMA is extremely low due to the fact that the transformed β^′₁(18R)${{\beta }^{\prime }}_1(18\text{R})$ martensite has only an ordered 9R structure with stacking faults. The Cu–14.0Al–4Ni SMA exhibits a relative increase in the inherent and intrinsic damping capacity because the transformed γ^′₁(2H)${{\gamma }^{\prime }}_1(2\text{H})$ martensite exhibits twinning with abundant moveable twin boundaries.     

Synthesis of nanocrystalline CeAlO3 by solution-combustion route

CeAlO₃ was synthesised by a modified solution-combustion route using a mixture of urea and glycine as fuel. A trivalent oxidation state of cerium was stabilised and high-quality single phase polycrystalline CeAlO₃ was obtained by optimising the ratio of fuels. The transmission electron micrography and powder X-ray diffraction investigations showed that the particles were nanocrystalline in nature. Rietveld refinement confirmed the space group of the structure to be I4/mcm$I4/mcm$ with lattice parameters a=5.3278(1)$a=5.3278(1)$ Å, c=7.5717(3)$c=7.5717(3)$ Å. Magnetisation measurements indicated that the sample was paramagnetic up to 2 K. The susceptibility data fitted the Curie–Weiss model in the temperature range 100–300 K with _θp=−40${\theta }_p=-40$ K. The value of _μeff=2.2_μB${\mu }_{\text{eff}}=2.2{\mu }_B$ was close to that expected for a Ce³⁺ ion. The magnetic properties were comparable to that reported for single crystals indicating the high quality of CeAlO₃ prepared in the present work. The semiconducting band gap as estimated from UV–visible spectroscopy was 3.26 eV.     

Enhanced photocatalytic activity of sulfur doped TiO2 for the decomposition of phenol: A new insight into the bulk and surface modification

Sulfur ion (S⁶⁺) was doped into the anatase TiO₂ prepared by sol–gel method (SG-TiO₂) using sulfur powder as a sulfur source (S-TiO₂) and its photoreactivity was probed for the degradation of phenol under UV/solar light illumination. The S-TiO₂ and SG-TiO₂ were characterized by PXRD, UV–vis DRS, FTIR, SEM, XPS, BET and PL techniques. It was observed that S⁶⁺ ion was incorporated into the TiO₂ crystal lattice at Ti⁴⁺ lattice site and the sulfur on the surface gets modified to ₄SO²⁻${{\text{SO}}_4}^{2-}$ due to the heat treatment under atmospheric conditions. The high photocatalytic activity of S-TiO₂ compared to SG-TiO₂ is attributed to the surface modification of sulfur as sulfate which plays a crucial role in trapping electrons. S-TiO₂ shows significant increase in the surface area, reduced crystallite size, increased surface acidity, visible light absorption and prolonged lifetime of the photogenerated charge carriers. Hole scavengers like potassium iodide and tertiary butanol suggested the surface degradation mechanism rather than the bulk degradation pathway. Addition of oxidizing agents to the degradation reaction did not show any enhancement in the degradation rates since the presence of ₄SO²⁻${{\text{SO}}_4}^{2-}$ on the TiO₂ surface itself acts as the efficient electron trapping centers. Both trapping and detrapping of the electron takes place more efficiently at ₄SO²⁻${{\text{SO}}_4}^{2-}$ centers. The enhanced activity of S-TiO₂ is attributed to the synergistic effect between S⁶⁺ dopant with surface modified ₄SO²⁻${{\text{SO}}_4}^{2-}$.     

Fabrication,characterization and electrochemistry of organic–inorganic multilayer films containing polyoxometalate and polyviologen via layer-by-layer self-assembly

The novel organic–inorganic multilayer films containing poly(butanyl viologen) (abbreviated as PBV) and phosphomolybdic acid (H₃PMo₁₂O₄₀, abbreviated as PMo₁₂) have been fabricated on quartz slides, silicon wafers and glassy carbon electrode by the layer-by-layer self-assembly technique. The highly ordered multilayer films were characterized by the UV–visible spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR), Atomic force microscopy (AFM) and cyclic voltammetry. UV–visible spectra revealed that the growth of the films for each deposition cycle was reproducible. FT-IR and XPS spectra confirmed the incorporation of PBV and PMo₁₂ into the multilayer films. XRR revealed the film thickness at nanoscale, and AFM showed film surface with uniform and smooth morphology. In addition, the electrochemical behavior of the multilayer films at room temperature was investigated. As a result, the films presented good electrocatalytic activity toward ₃BrO⁻${{\text{BrO}}_3}^{-}$, H₂O₂ and ₂NO⁻${{\text{NO}}_2}^{-}$, providing valuable information for exploring the potential applications in ₃BrO⁻${{\text{BrO}}_3}^{-}$ sensors.     

Heats of Hydrolysis and Formation of Dimethoxychloroborane

The heat of hydrolysis of dimethoxychloroborane has been measured; for the reaction, (CH3O)2BCl(liq)+3H2O(liq)=H3BO3(c)+2CH3OH(liq)+HCl(g)ΔH(25°C)=−26.6±0.8kj/mole=−6.4±0.2kcal/mole.From this, we have calculated the heat of formation of dimethoxychloroborane: for the liquid, ΔHf° (25 °C) = −782.1 ± 1.8 kj/mole (−186.9±0.4 kcal/mole), and for the gas, ΔHf° (25 °C) = −747.9 ±2.2 kj/mole (−178.8±0.5 kcal/mole).     

Heats of Hydrolysis and Formation of Potassium Borohydride

The heat of reaction of potassium borohydride with 0.060 molal HCl has been measured by solution calorimetry. The heat of solution of the hydrolysis products has also been measured and combined with certain literature values to calculate the process: KBH4(c)+HCl(g)+3H2O(liq)→KCl(c)+H3BO3(c)+4H2(g),ΔH°(25°C)=−354.06±1.84kj/mole(−84.62±0.44kcal/mole).A combination of this value with literature values for the heats of formation of HCl(g), H₂O(liq), KCl(c), and H₃BO₃(c) gives for KBH₄(c): ΔHf°(25°C) = ?228.86 ± 2.30 kj/mole(?54.70 ± 0.55 kcal/mole).Other data on the heats of formation of the alkali-metal borohydrides are discussed briefly.     

An investigation of V2O5/polypyrrole composite cathode materials for lithium-ion batteries synthesized by sol–gel

A lamellar compound of V₂O₅ was prepared by a simple sol–gel method using H₂O₂ and V₂O₅ as starting materials. The composites of V₂O₅/PPy (polypyrrole) were synthesized by in situ polymerization, and characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrum, and X-ray diffraction (XRD). The electrochemical properties of the composites were investigated with galvanostatic charge–discharge test, cyclic voltammetry and A.C. impedance techniques. The results show that pyrrole was uniformly polymerized around the V₂O₅, and the V₂O₅/PPy composite possessed excellent electrochemical performance. The specific discharge capacity of the 2.5% mass percent PPy composites (271.8 mAh g⁻¹) was higher than that of pure V₂O₅ (247.6 mAh g⁻¹) at 0.1C rate and it has the voltage limits of 1.8–4.0 V. Furthermore, the specific discharge capacity remained at 225.4 mAh g⁻¹ after 50 cycles. The chemical diffusion coefficient D_Li⁺$D_{{\text{Li}}^{+}}$ values were calculated, depending on x-values in Li_x+1.1V₂O₅. The values of D_Li⁺$D_{{\text{Li}}^{+}}$ range from 2.18 × 10⁻¹² cm² s⁻¹ to 4.5 × 10⁻¹⁴ cm² s⁻¹ for V₂O₅/PPy composite, and it decreased as the amount of intercalated Li⁺ increased.     

A Correlation Between [Rh(III)X6-n(H2On]n-3 (n=O, 1, 2) Complexes and the Photographic Properties of AgX Emulsions

Abstract

$${[Rh(III)X_{{}_{6?n}}{(H_{2}O)}_n]}^{n?3}$$ (n-0, 1, 2) complexes (except $$RhC{l}_5{(H_{2}O)}^{2?}$$) were stabilized in aqueous solution by examining the halogen-ion concentration dependency of the rhodium com-plexes using visible absorption spectrum analysis. The effects of different Rh(lll) complexes on the sensitivity of photographic cubic and tabular AgX emulsions were investigated to determine the photographic criteria of Rh(lll) doping effects. The relative sensitivity for cubic AgCI and AgBr emulsions was found to increase by about 2-3 times the $$H_{2}O$$ coordination number for $${[Rh(III)X_{{}_{6?n}}{(H_{2}O)}_n]}^{n?3}$$ (n = 0, 1, 2), as compared with a standard AgX emulsion containing $${[Rh{X}_6]}^{3?}$$. For tabular AgBr grains, the desensitization was of the order of 10^-4 times, compared with a standard raw AgBr emulsion and was independent of the Rh(lll)-complex species. A mechanism is proposed for the desensitization produced by adding $${[Rh(III)X_{{}_{6?n}}{(H_{2}O)}_n]}^{n?3}$$ (n – 0, 1, 2) complexes to the AgX grain in the emulsions.     

Franck-Condon Factors to High Vibrational Quantum Numbers I: N2 and [... formula ...]

Franck-Condon factor arrays have been computed numerically to high vibrational quantum numbers for the band systems N2:C3II−B3II(Second Positive)N2:B3II−A3∑(First Positive)N2:A3∑−X1∑(Vegard Kaplan)N2:a1II−X1∑(Lyman-Birge-Hopfield)N2+;A2II−X2∑(Meinel)N2+:B2∑−X2∑(First Negative)and for the following ionization transitions N2X1∑→N2+X2∑N2X1∑→N2+A2IIN2X1∑→N2+B2∑     

Heat of Formation of N-Dimethylaminodiborane

The heat of reaction of N-dimethylaminodiborane with water has been determined according to the reaction: (CH3)2NB2H5(g)+6H2O(liq)=(CH3)2NH(g)+2H3BO3(c)+5H2(g),ΔH(25°C)=−374.99±2.71kj/mole=−89.62±0.65kcal/mole.A combination of this value with the heat of vaporization, and with the heats of formation of boric acid, dimethylamine, and water gives for liquid N-dimethylaminodiborane: ΔHf°(25 °C) = ?36.22 ± 0.75 kcal/mole.     

Ba(OH)2 Equilibria in the System Ba-O-H-F,With Application to the Formation of Ba2YCu3O6.5 + x From BaF2-Precursors

The ex situ process for fabricating Ba₂YCu₃O_{6.5 + x} superconducting tapes from BaF₂- based precursors involves a hydration/oxidation reaction at ≈730 °C to 750 °C generally written as: (2BaF2+Y+3Cu)(amorphous)+(2H2O+2.25O2)(g)→Ba2YCu3O6.5+x(s)+4HF(g).However, microscopic observations of partially processed films suggest the presence of a transient liquid phase during conversion. Alternatively, the conversion reaction can be rewritten as the sum of several intermediate steps, including the formation of a barium hydroxide liquid: (BaF2)(amorphous)+2H2O(g)→Ba(OH)2(liq)+2HF(g).To evaluate the possibility of a hydroxide liquid conversion step, thermodynamic calculations on the stability of Ba(OH)₂(liq) have been completed from 500 °C to 900 °C at 0.1 MPa p_total. Based on currently available data, the calculated phase diagrams suggest that a viable hydroxide reaction path exists in the higher part of this temperature range. The calculations indicate that Ba(OH)₂(liq) may be stable at log p_H2O (Pa) values from ≈4 to 5, provided log p_HF (Pa) values can be maintained below 0 to −1. Limited experimental confirmation is provided by results of an experiment on BaF₂(s) at 815 °C, 0.1 MPa p_H2O, in which essentially all F at the surface was replaced by O. It is therefore possible that processing routes exist for producing Ba₂YCu₃O_{6.5 + x} based on the presence of a Ba(OH)₂ liquid, which might have an effect on conversion rates and texturing in the superconducting film.