Study of electronic structure and Compton profiles of PbS and PbSe

In this paper, we report the energy bands, density of states and the first ever Compton profiles of PbS and PbSe computed in the framework of spin-polarised relativistic Korringa–Kohn–Rostoker and ab initio pseudopotential with Hartree–Fock and density functional theory schemes. In addition, we have computed the energy bands and density of states using full-potential linearised augmented plane wave method. To compare our theoretical data, we have also measured the first ever isotropic Compton profiles at an intermediate resolution using our 740 GBq (20 Ci) ¹³⁷Cs Compton spectrometer. The Compton profiles scaled on equal-valence-electron-density show that PbSe is more covalent than PbS, which is in agreement with the present Mulliken's population data.     

On the formation of β-FeOOH (akaganéite) in chloride-containing environments

Fe(III) oxyhydroxides were synthesised in chlorinated environments via chemical or electrochemical processes in order to determine the conditions favouring the formation of akaganéite. Corrosion products were characterised using X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The first method produced Fe(III) oxyhydroxides from the aerial oxidation of iron(II) precipitates which were obtained by mixing FeCl₂ · 4H₂O and NaOH solutions. Depending on the initial amounts of Fe²⁺, Cl⁻ and OH⁻, goethite, lepidocrocite or akaganéite were then obtained. When a large excess of dissolved FeCl₂ was present, akaganéite was formed independently of the oxygen flow. In the second method, steel electrodes were left in baths containing chloride with [Cl⁻] = 2 mol L⁻¹, using either FeCl₂ · 4H₂O or NaCl. Akaganéite was obtained exclusively in the FeCl₂ solutions, confirming that to obtain the formation of this compound, both iron(II) and chloride concentrations must be important.     

Field emission enhancement of ZnO nanorod arrays with hafnium nitride coating

Vertically well-aligned single crystal ZnO nanorod arrays were synthesized and enhanced field electron emission was achieved with hafnium nitride (HfN_x) coating under proper sputtering condition. HfN_x films with various composition have been coated on ZnO nanorod arrays using a reactive direct current (DC) magnetron sputtering system. Morphology and crystal configuration of the ZnO nanorod arrays were investigated by scanning electron microscopy and X-ray diffraction. The field emission properties of the coated and uncoated ZnO nanorod arrays were characterized. The as-grown ZnO nanorod arrays showed a turn-on electric field of 6.60 V μm^− 1 at a current density of 10 μA cm^− 2 and an emission current density of 1 mA cm^− 2 under the field of 9.32 V μm^− 1. While the turn-on electric field of the coated ZnO nanorod arrays sharply decreased to 2.42 V μm^− 1, an emission current density of 1 mA cm^− 2 under the field of only 4.30 V μm^− 1 can be obtained. A method to accurately measure the work function of the coated films was demonstrated.     

AC corrosion - Part 1: Effects on overpotentials of anodic and cathodic processes

AC-induced corrosion is a controversial subject and many aspects of it need to be clarified, first and foremost, the mechanism and relationship between AC density and corrosion rate. This paper (Part 1) presents and discusses the effects of AC interference on kinetics parameters; the effects on corrosion rate and corrosion mechanism will be discussed in Part 2. Polarisation curves were obtained in different solutions (soil-simulating solution, 35 g L⁻¹ NaCl, 1 M FeSO₄, 1 M CuSO₄ and 1 M ZnSO₄) on different metallic materials (carbon steel, galvanised steel, zinc and copper) in the presence of AC interference (30-1000 A/m²).     

Composition and structure of Al ions implanted Fe at elevated temperatures

Al ions with ion energy of 120 keV are implanted into Fe under ion current density of 3.18 μA/cm² to implantation doses of 5 × 10¹⁶ and 1 × 10¹⁷ ions/cm² at room temperature and elevated temperatures of 250 and 500 °C, respectively. At 250 °C, the distribution depth of implanted Al reaches 160 nm with a peak concentration of 6 at.% at the dose of 5 × 10¹⁶ ions/cm², and 180 nm with 10 at.% at 1 × 10¹⁷ ions/cm², analyzed by Rutherford backscattering spectroscopy, respectively. At 500 °C, the implantation depth is 200 nm and the maximum concentration of Al is 10 at.% at the dose of 1 × 10¹⁷ ions/cm². With 5 × 10¹⁶ ions/cm², the intermetallics Al₁₃Fe₄ is formed in the Fe samples at 500 °C, revealed by X-ray diffraction. With 1 × 10¹⁷ ions/cm², the phase is also detected at 250 °C. The concentration-depth profiles of implanted Al in Fe samples at the room temperature, 250 °C and 500 °C are calculated by a mass transfer model that is built based on the transport of ions in matter and the irradiation enhanced diffusion. The calculated concentration-depth profiles are in reasonable agreement with those obtained from the experiments.     

Dual role of the six-coordinated lead and copper ions in structure of the copper-lead-tellurate glasses

Glasses from xCuO·(100 − x)[4TeO₂·PbO₂] system where x = 0-40 mol% were studied by density measurements, FTIR, UV-vis and EPR spectroscopy in order to obtain information about the changes that appear in the structure of matrix glass with the doping of copper ions.The FTIR data analysis shows that the copper ions will be distributed in the six-coordinated interstices ([PbO₆] structural units) and some [TeO₄] structural units will be converted to [TeO₃] structural units because the lead ions have a strong affinity towards these groups containing non-bridging oxygens, with negative charge.From the EPR studies, we can conclude that Cu⁺² ions have an environment elongated along the z-axis and the ground state of the Cu⁺² is dx²−y² orbital (²B_1g state). When the concentration of CuO is increased beyond 5 mol%, the intensity and width of both the parallel and perpendicular hyperfine components are observed to increase.     

Hydrogen permeation behavior in pure nickel implanted with phosphorus, sulphur and their mixture

The entry and transport of hydrogen in phosphorus (P)-, sulphur (S)- and their mixture (P + S)-implanted nickel specimens with a fluence range of 1 × 10¹⁵ to 1 × 10¹⁷/cm² have been investigated using an electrochemical permeation technique and etching treatment (0.2% HF solution). From the hydrogen permeation transients obtained, the effective hydrogen concentration (C_H), apparent hydrogen diffusion coefficient (D_lag) and breakthrough time (t_lag) were estimated by using the time lag method in addition to the steady state permeation current density (P_∞). It was found that at a fluence of less than 1 × 10¹⁶/cm² almost all hydrogen permeation transients of the implanted nickel specimens were affected by the defects (vacancy, compressive stress and so on) generated during ion implantation process. At a high fluence of 1 × 10¹⁷/cm² the hydrogen permeation transient had a specific behavior because of the formation of amorphous phase for P, the structure change from fcc-structure to bcc-structure for S and both of them for the mixture (P and S). However, a synergistic effect of P and S was not observed on the hydrogen permeation transient. The behavior of these parameters depending on fluence and implanting element was discussed in terms of an amount of hydrogen entry site, the degree of defects, the properties of amorphous phase and structure and so on.     

Corrosion resistance of TiO2 films grown on stainless steel by atomic layer deposition

Titanium dioxide (TiO₂) films have been deposited onto stainless steel substrates using atomic layer deposition (ALD) technique. Composition analysis shows that the films shield the substrates entirely. The TiO₂ films are amorphous in structure as characterized by X-ray diffraction. The electrochemical measurements show that the equilibrium corrosion potential positively shifts from − 0.96 eV for bare stainless steel to − 0.63 eV for TiO₂ coated stainless steel, and the corrosion current density decreases from 7.0 × 10^− 7 A/cm² to 6.3 × 10^− 8 A/cm². The corrosion resistance obtained by fitting the impedance spectra also reveals that the TiO₂ films provide good protection for stainless steel against corrosion in sodium chloride solution. The above results indicate that TiO₂ films deposited by ALD are effective in protecting stainless steel from corrosion.     

Theoretical studies on the spectroscopic properties of a series of halide Zinc (II) complexes with pyridinylimine and pyridinylmethylamine derivatives

The ground structures of pyridinylimine derivatives (L1-a = N-(pyridin-2-ylmethylene)aniline and L1-b = N¹,N¹-(dimethyl-N⁴-pyridin-2-ylmethylene)benzene-1,4-diamine) and pyridinylmethylamine derivatives (L2-a = N-(pyridin-2-ylmethyl)aniline and L2-b = N¹,N¹-(dimethyl-N⁴-pyridin-2-ylmethy)benzene-1,4-diamine) and their corresponding Zn (II) complexes ([Zn(L1-a)Cl₂] (A), [Zn(L1-b)Cl₂] (B), [Zn(L2-a)Cl₂] (C), and [Zn(L2-b)Cl₂] (D)) are optimized at three DFT levels, i.e., B3LYP, B3PW91, and M06. The spectroscopic properties are calculated using time-dependent density functional theory (TD-DFT) in gas and in solution. The occupied orbitals involved in the transitions have mixed character of the Cl atom p orbital and ligand-based π orbital, while the lowest unoccupied molecular orbital (LUMO) presents π* orbital character. Two UV–Vis absorption peaks located at 252 and 353 nm are assigned to (p, π) → π* transition with mixed intraligand charge-transfer (ILCT)/ligand–ligand charge-transfer (LLCT) character and π → π* transition with ILCT character for complex A, respectively. With respect to complex B, the absorption bands show red shift with two peaks at 281 and 470 nm with the appearance of an electron-releasing group (–N(CH₃)₂) because the energy gap (ΔE|HOMO–LUMO|) is decreased. Red shift phenomenon is also observed between other two complexes C and D. Comparison between theoretical and experimental results for the structures and spectra is discussed in detail.     

Organoheterobimetallic cyanodithioimidocarbonates and their I2-doped products: Synthesis,characterization and conducting properties

Complexes of the type [PhHg]₂[M(cdc)₂], [Me₂Sn][M(cdc)₂], [n-Bu₂Sn][M(cdc)₂], [n-Bu₃Sn]₂[M(cdc)₂] and [Ph₃Sn]₂[M(cdc)₂] (M = Ni(II) and Cu(II); cdc²⁻ = cyanodithioimidocarbonate) and their I₂-doped products have been prepared and characterized by microanalysis, magnetic and solution as well as solid phase conductivity measurements, IR, Raman, electronic, ¹H and ¹³C NMR and ESR spectroscopic techniques. ESR silent diamagnetic compounds [PhHg]₂[Cu(cdc)₂], [Me₂Sn][Cu(cdc)₂], [n-Bu₂Sn][Cu(cdc)₂], [n-Bu₃Sn]₂[Cu(cdc)₂] and [Ph₃Sn]₂[Cu(cdc)₂] are strongly antiferromagnetically coupled. [PhHg]₂[Ni(cdc)₂] is weakly paramagnetic because of the weak axial interactions of sulfur atoms of the ligand cdc²⁻ with some of the Ni(II) centers. Sharp ¹H NMR signals suggest that [PhHg]₂[Cu(cdc)₂], [n-Bu₂Sn][Cu(cdc)₂], [n-Bu₃Sn]₂[Cu(cdc)₂] and [Ph₃Sn]₂[Cu(cdc)₂] remained diamagnetic in solution as well. Majority of the complexes exhibited σ_rt in the range of 10⁻¹¹ to 10⁻¹⁰ S cm⁻¹ while the I₂-doped products show enhanced conductivity in the 10⁻¹⁰ to 10⁻⁶ S cm⁻¹ range and exhibit semiconducting behaviour.     

Formation, fast oxidation and thermodynamic data of Fe(II) hydroxychlorides

Iron(II) hydroxide and hydroxychloride precipitates were obtained by mixing FeCl₂ · 4H₂O and NaOH aqueous solutions with various concentration ratios R′ = [Cl⁻]/[OH⁻] = 2 [FeCl₂]/[NaOH] at [NaOH] = 0.4 mol L⁻¹. They were analysed by Infrared spectroscopy after 24 h of ageing at room temperature. Fe(OH)₂ was obtained alone only for the smallest values of R′, typically R′ ? 1.16. β-Fe₂(OH)₃Cl formed as soon as R′ ? 1.40 and was obtained alone for R′ ? 2.25. The initial precipitates were oxidised by addition of a small amount of hydrogen peroxide (5 mL of an aqueous solution containing approximately 30 vol% H₂O₂) instead of O₂. The action of H₂O₂ on Fe(OH)₂ gave rise to δ-FeOOH as already reported. Its action on Fe(II) hydroxychlorides gave rise to akaganéite β-FeO_1−2x(OH)_1+xCl_x. A transformation of the two-phase system found at R′ = 1.5 after long ageing times (6 months) was observed and β-Fe₂(OH)₃Cl remained alone. This slow transformation of Fe(OH)₂ into β-Fe₂(OH)₃Cl may explain why β-Fe₂(OH)₃Cl was only reported as a corrosion product on iron archaeological artefacts. Finally, the respective domains of stability of Fe(OH)₂ and β-Fe₂(OH)₃Cl were demarcated and an estimation of the standard Gibbs free energy of formation of β-Fe₂(OH)₃Cl could be given: .     

Fermi surface topology of deuterium-doped vanadium: Compton scattering study

The deuteration-induced effect on the Fermi surface (FS) topology of V was investigated by the synchrotron-based Compton scattering technique with 115 keV X-rays. The three-dimensional occupation number density (OND) of α-VD_0.64 single crystal and V single crystal was reconstructed by the directional Compton profiles along 13-18 directions. The observed OND shows that the FS topology of α-VD_0.64.differs from that of V at Γ, N, and H points in the crystal momentum space, which are hole position for V. This indicates that electrons that originate from deuterium modify the upper part of the host metal d bands (3rd and 4th bands) at the Fermi level E_F, and forms the metal-hydrogen bonding states with the lower part of the host metal d band (1st band).     

Corrosion behaviour of zinc deposits obtained under pulse current electrodeposition: Effects of coumarin as additive

The corrosion behaviour of zinc deposits obtained under pulsed current electrodeposition from an acidic chloride bath in the presence and absence of coumarin has been investigated. The effects of pulse peak current density (J_p) on the morphology of zinc deposits were studied by scanning electron microscopy. An increase in J_p from 40 to 280 A dm⁻² yields deposits with a finer grain size. The refinement of the grain size was more considerable in the presence of coumarin (J_p = 280 A dm⁻²). The preferred orientation of zinc deposits was studied by X-ray diffraction. At J_p = 40 A dm⁻², the preferred orientation of zinc deposits was (1 0 3) and changed to (0 0 2) at J_p = 80 A dm⁻². An increase in J_p to 280 A dm⁻² did not change the preferred crystallographic orientations except for an increase in the peak intensity of the (0 0 2) plane. In the presence of coumarin, the preferred crystallographic orientations changed at J_p = 280 A dm⁻² from the (0 0 2) plane to the (1 0 3) plane. The corrosion behaviour was investigated in an aerated 3.5% NaCl solution; the anodic polarization and electrochemical impedance spectroscopy curves were performed. The corrosion resistance of zinc deposits was improved by increasing the pulse peak current density (J_p); whereas, the presence of coumarin did not improve the corrosion resistance.     

Characterisation of mackinawite by Raman spectroscopy: Effects of crystallisation, drying and oxidation

Iron(II) sulphides were precipitated by mixing FeCl₂ · 4H₂O (or FeSO₄ · 7H₂O) and Na₂S aqueous solutions with various [Fe(II)]/[S(-II)] concentration ratios at [Fe(II)] = 0.1 mol L⁻¹. They were analysed by micro-Raman spectroscopy and X-ray diffraction immediately after precipitation and after various times of ageing in suspension at room temperature. In any case, the initial precipitate was nanocrystalline mackinawite. Its Raman spectrum is made of two sharp peaks at 208 ± 1 and 282 ± 1 cm⁻¹. For [Fe(II)]/[S(-II)] ? 1, ageing of the precipitate led to crystalline mackinawite, as testified by X-ray diffraction. The Raman spectrum of crystalline Fe(II) mackinawite shows three main peaks at 208, 256 and 298 cm⁻¹. Drying of nanocrystalline mackinawite under an argon flow favoured crystallisation. The removal of interparticle and surface adsorbed water molecules led to coalescence of the nanoparticles and increase of the size of the domains of coherent scattering. For [Fe(II)]/[S(-II)] = 1/2, the precipitate still consisted of nanocrystalline mackinawite after 70 days of ageing. Finally, the early oxidation stages of mackinawite led to the formation of Fe(III) cations inside the tetrahedral sites of the crystal structure. The most oxidised form of Fe(III)-containing mackinawite is characterised by a Raman spectrum with sharp peaks at 125, 175, 256, 312 and 322 cm⁻¹, and a large vibration band at 350-355 cm⁻¹ that may be attributed to stretching modes of Fe(III)-S tetrahedrons. Analyses of the rust layers of a roman ingot that remained 20 centuries in the Mediterranean Sea revealed the presence of iron sulphides, more likely generated by sulphate-reducing bacteria. Micro-Raman analyses demonstrated the presence of nanocrystalline mackinawite and Fe(III)-containing mackinawite.     

The characterisation of the protective film formed by benzotriazole on the 90/10 copper-nickel alloy surface in H2SO4 media

The nature of the protective film formed by benzotriazole (BTAH) on the surface of the 90/10 CuNi alloy in deaerated 0.5 mol L⁻¹ H₂SO₄ solution containing Fe(III) ions as oxidant was investigated by weight-loss, calorimetric measurements, and by surface-enhanced Raman spectroscopy (SERS). The SERS measurements show that the protective film is composed by the [Cu(I)BTA]_n polymeric complex and that the BTAH molecules are also adsorbed on the electrode surface. A modification of the BET isotherm for adsorption of gases in solids is proposed to describe the experimental results obtained from weight-loss experiments that suggest an adsorption in multilayers. Electrochemical studies of copper and nickel in 0.5 mol L⁻¹ H₂SO₄ in presence and absence of BTAH have also been made as an aid to interpret the results. The calculated adsorption free energy of the cuprous benzotriazolate on the surface of the alloy is in accordance with the value for pure copper.     

Synthesis and consolidation of TiN/TiB2 ceramic composites via reactive spark plasma sintering

The simultaneous synthesis and densification of TiN/TiB₂ ceramic composites via reactive spark plasma sintering (RSPS) was investigated. Different component ratios (TiH₂/BN (TiN, B)) and heating rates (112.5-300 °C/min) were used to initiate the chemical reaction for TiN/TiB₂ synthesis. The omit RSPS process was revealed to have three stages, which are described separately. The relationships between the RSPS conditions, the microstructure and the properties of sintered ceramic composites were established. A Vickers hardness of 16-25 GPa and a fracture toughness of 4-6.5 MPa m^1/2 were measured for various compositions. Sintered ceramic composites containing 36 wt% TiB₂ with the highest relative density of 97.4 ± 0.4% and an average grain size of 150-550 nm have been obtained.     

Evaluation of metastable pitting on titanium by charge integration of current transients

The metastable pitting of titanium has been studied under potentiostatic control in solutions containing chloride ions. An approach based on the charge integration of current transients was proposed for a quantitative determination of metastable pitting. A pit density (d_mpit) was defined as the number of metastable pits per unit area per unit time (cm⁻² h⁻¹) with a typical size, instead of a size distribution. The calculated d_mpit of titanium at 0.5 V_SCE in 0.6 M NaCl was about 1.0 × 10³ cm⁻² h⁻¹ with a typical radius of 0.12 μm. An exponential potential dependence of d_mpit was obtained through the integration approach.     

Synthesis, crystal and band structures, and optical properties of a new framework mercury pnictides: [Hg4As2](InBr3.5As0.5) with tridymite topology

A new framework compound, [Hg₄As₂](InBr_3.5As_0.5) (1), has been prepared by the solid-state reaction of Hg₂Br₂ with elemental In and As at 450 °C. Compound 1 crystallizes in the space group P₆₃/mmc of the Hexagonal system with two formula units in a cell: a = b = 7.7408(6) Å, c = 12.5350(19) Å, V = 650.47(12) Å³. The crystal structure of 1 features a novel 3D framework, [Hg₄As₂]²⁺ with tridymite topology. The optical properties were investigated in terms of the diffuse reflectance and infrared spectra. The electronic band structure along with density of states (DOS) calculated by DFT method indicates that the present compound is semiconductor, and the optical absorption is mainly originated from the charge transitions from Br-4p and As-4p states to Hg-6s and In-5p states.     

Synthesis of the pyrrolo[3,2-b]pyrrole-based copolymer with enhanced open circuit voltage

A new accepter unit, pyrrolo[3,2-b]pyrrole-2,5-dione, was prepared and utilized for the synthesis of the conjugated polymer containing electron donor–acceptor pair for OPVs. Pyrrolo[3,2-b]pyrrole-2,5-dione unit, regioisomer of the known pyrrolo[3,4-c]pyrrole-1,4-dione, is originated from the structure of stable synthetic pigment. The new conjugated polymer with pyrrolo[3,2-b]pyrrole-2,5-dione, thiophene and carbazole was synthesized using Suzuki polymerization to generate P1. The solid thin film of P1 shows absorption band with maximum peaks at 374 and 548 nm, and the absorption onset at 679 nm, corresponding to band gap of 1.83 eV. The field-effect hole mobility of P1 is 2.2 × 10⁻⁵ cm²/Vs. The device based on the polymer:PCBM (1:2) blend without thermal treatment showed a V_OC of 0.82 V, a J_SC of 6.28 mA/cm², and an FF of 0.39, giving a PCE of 2.00%.     

Oxidation of stainless steel 304L in carbon dioxide

Oxidation of 304L stainless steel in a carbon dioxide atmosphere at 10⁵ Pa has been studied. Between 1193 and 1293 K the oxidation kinetics exhibit first a rapid increase, then a parabolic behaviour with apparent activation energy of (209 ± 8) kJ mol⁻¹ and obeys a Langmuir pressure law. After 1.15 mg cm⁻², the kinetics become almost linear.The reaction products are chromia at the grain boundaries, wüstite (Fe_1−xO) on the surface for weight gains greater than 0.30 mg cm⁻² and chromite. The very complex reaction mechanism takes into account random buckling for weight gains >1.15 mg cm⁻².