Adsorption and dissociation of N2O molecule on Fe(1 1 1) surface: A DFT study

We have used spin-polarized density functional theory to investigate the adsorption and dissociation of N₂O molecule on Fe(1 1 1) surface. Several adsorption geometries and sites were examined in detail. In our computational results, the Fe–N₂O–η²-[N_t(1,2), O_t(1)] exhibited the greatest adsorption energy, 1.16 eV, on Fe(1 1 1) surface, whereas the other binding modes still have effective adsorption and dissociation behaviors. For the N₂O dissociation mechanisms, our calculated results indicate that the most favorable pathway is the production of N₂ + O fragments on the Fe(1 1 1) surface. Formation of NO + N is also possible, although this pathway involves a higher energy barrier.     

Formaldehyde on TiO2 anatase (1 0 1): A DFT study

The adsorptions of formaldehyde molecule on the stoichiometric anatase TiO₂ (1 0 1) surface have been studied by first principles calculations. Four types of adsorption have been investigated at 0.25 ML coverage. Two of them are chemical adsorptions and the other two are physical adsorptions. For the chemical adsorptions, C, O atoms in the formaldehyde molecule form two bonds with the O_2c/O_3c and Ti_5c on the anatase (1 0 1) surface. The CO bond in the formaldehyde molecule is elongated and a dioxymethylene structure forms in the two chemical adsorptions. The OTi_5c interaction can be found in the two physical adsorptions and it is the only contacting point at the interface. No serious internal distortion in the formaldehyde molecule can be found in the physical adsorptions. The LDOS and the difference of the charge density are calculated to investigate the interface bonds of the adsorption. As the adsorption coverage increase, the molecules on the surface repel each other and weaken the adsorptions. For example, the chemical adsorption may become physical adsorption at high coverage.     

First principles study of interface structure and electronic property of Au/SrTiO3(0 0 1)

First principles method is carried out to study the interface structure and electronic property of nine probable Au/SrTiO₃(0 0 1) models. It is revealed that besides O or Ti vacancies having to exist in the interface, the interface energy and bonding nature are strongly dependent on the atomic configurations at interface. Such interfacial configurations in which each Au atom in the upper Au layer bonds with each O atom in the TiO₂-terminated SrTiO₃(0 0 1) under layer would be preferable to be formed. From the analysis of the electronic structure of the defective Au/SrTiO₃(0 0 1) interfaces, the interactions between Au and various vacancies on SrTiO₃(0 0 1) interface are very different.     

Synthesis,structural characterization and photophysical properties of highly photoluminescent crystals of Eu(III), Tb(III) and Dy(III) with 2,5-thiophenedicarboxylate

Lanthanide compounds of general formula [Ln₂(2,5-tdc)₃(dmf)₂(H₂O)₂]·2dmf·H₂O (Ln = Eu(III) (1), Tb(III) (2), Gd(III) (3) and Dy(III) (4), dmf = N,N′-dimethylformamide and 2,5-tdc²⁻ = 2,5-thiophedicarboxylate anion) were synthesized and characterized by elemental analysis, X-ray powder diffraction patterns, thermogravimetric analysis and infrared spectroscopy. Phosphorescence data of Gd(III) complex showed that the triplet states (T₁) of 2,5-tdc²⁻ ligand have higher energy than the main emitting states of Eu(III), Tb(III) and Dy(III), indicating that 2,5-tdc²⁻ ligand can act as intramolecular energy donor for these metal ions. An energy level diagram was used to establish the most relevant channels involved in the ligand-to-metal energy transfer. The high value of experimental intensity parameter Ω₂ for the Eu(III) complex indicate that the europium ion is in a highly polarizable chemical environment. The emission quantum efficiency (η) of the ⁵D₀ emitting level of Eu(III) was also determined. The complexes act as possible light conversion molecular devices (LCMDs).     

On the synthesis and dielectric studies of (1 − x)Bi(Mg1 / 2Zr1 / 2)O3 − xPbTiO3 piezoelectric ceramic system

Scandium free piezoelectric ceramics of the composition (1 − x)Bi(Mg_1 / 2Zr_1 / 2)O₃ − xPbTiO₃ (BMZ − xPT) were fabricated by the solid state reaction method. Dielectric and structural properties were measured and phase diagram was constructed from the temperature dependent dielectric and impedance data. The morphotropic phase boundary (MPB) was found to be located in the range 0.55 < x < 0.60 with paraelectric–ferroelectric phase transition temperature, T_C (∼ 280 °C). The ceramics near the MPB showed high room temperature dielectric constant (∼ 1387). The room temperature values of the remanent polarization (P_r) and coercive filed (E_C), were ∼ 29 μC/cm² and ∼ 23 kV/cm, respectively.     

Structural,thermal, spectroscopic and magnetic studies of the (C2N2H10)0.5[FexV1−x(HPO3)2] (x = 0.26, 0.52, 0.74) solid solution

The (C₂N₂H₁₀)_0.5[Fe_xV_1−x(HPO₃)₂] (x = 0.26, 0.52 0.74) compounds have been obtained by mild solvothermal conditions in the form of micro-crystalline powder with brown color. The crystal structures were refined by X-ray powder diffraction data using the Rietveld method. The compounds crystallize in the monoclinic system, space group P2/c with the unit-cell parameters, a = 9.262(5) Å, b = 8.823(5) Å, c = 9.714(6) Å, β = 120.84(3)°; a = 9.245(1) Å, b = 8.823(1) Å, c = 9.698(1)Å, β = 120.80(1)° and, a = 9.254(4)Å, b = 8.822(4)Å, c = 9.702(4)Å, β = 120.73(3)° for (C₂N₂H₁₀)_0.5[Fe_0.26V_0.74 (HPO₃)₂] (1), (C₂N₂H₁₀)_0.5[Fe_0.52V_0.48(HPO₃)₂] (2), and (C₂N₂H₁₀)_0.5[Fe_0.74V_0.26(HPO₃)₂] (3). The compounds show an open crystalline structure with three-dimensional character, whose formula for the anionic inorganic skeleton is [M(HPO₃)₂]²⁻. The inorganic framework is formed by [MO₆] octahedra inter-connected by phosphite groups. The structure of the compounds exhibits channels extended along the [1 0 0] and [0 0 1] directions and the ethylendiammonium cations are located inside these channels, linked through hydrogen bonds and ionic interactions. The infrared spectra show the bands corresponding to the stretching (P–H) vibration of the phosphite group and the band corresponding to the deformation mode of the ethylendiammonium cation, δ(NH₃⁺). The thermal and thermodiffractometric behavior show that the compounds are stable up to approximately 300 °C, at higher temperatures the decomposition of the crystal structure by calcination of the organic cation starts. The diffuse reflectance spectra show bands of the V³⁺ ion (d²), and a band of the Fe³⁺ ion (d⁵), in a slightly distorted octahedral symmetry. The values of the Dq and Racah parameters (B and C) have been calculated for the V(III) cation. Magnetic measurements were performed on a powdered sample from 5 to 300 K at magnetic fields 1000, 500 and 100 G, in the ZFC and FC modes. At the magnetic field of 1000 G antiferromagnetic interactions were observed, but at 100 G have been detected higher values of the χ_m in the FC mode than those observed in the ZFC one, indicating the existence of a dominant ferromagnetic component at low temperature. The magnetization measurements show hystheresis loops at 5 K, with values of the remanent magnetization and coercive field of 1.91 emu/mol and 23 Gauss for (1), 25 emu/mol and 300 Gauss for (2), and 3 emu/mol and 50 Gauss for the compound (3).     

Microwave dielectric ceramics in (Ca1− xBax)(Zn1 / 3Nb2 / 3)O3 system

(Ca_1−xBa_x)(Zn_1 / 3Nb_2 / 3)O₃ (x = 0–1.0) microwave dielectric ceramics were prepared and investigated. The Ba(Zn_1 / 3Nb_2 / 3)O₃-based solid solution was observed for x = 0.9, and the compositions with x = 0.1–0.7 resulted in the mixture of two phases. Dielectric constant ε_r and temperature coefficient of resonant frequency τ_f of the present ceramics varied anomalously and reached their maximum at x = 0.7–0.9, and these phenomena were originated from the partial substitution of small Ca²⁺ ions for larger Ba²⁺ at A-site. On the other hand, a good combination of microwave dielectric properties (ε_r = 36, Qf = 16,170 GHz, τ_f = − 12 ppm/°C) were obtained at x = 0.1, while the decreased Qf value was observed in other compositions.     

(C2N2H10)[FexV1−x(HPO3)F3] (x = 0.44, 0.72): Two new organically templated phosphites: Solvothermal synthesis and structural,thermal, spectroscopic and magnetic studies

(C₂N₂H₁₀)[Fe_xV_1−x(HPO₃)F₃] (x = 0.44, 0.72) have been synthesized using mild solvothermal conditions under autogenous pressure and the ethylenediamine molecule as templating agent. The crystal structures have been determined from X-ray single-crystal diffraction data. The compounds crystallize in the orthorhombic P2₁2₁2₁ space group with Z = 4 and unit-cell parameters a = 12.8494(9), b = 9.5430(6), c = 6.4372(5) Å, and a = 12.8578(1), b = 9.5342(1), c = 6.4370(7) Å for (C₂N₂H₁₀)[Fe_0.44V_0.56(HPO₃)F₃] and (C₂N₂H₁₀)[Fe_0.72V_0.28(HPO₃)F₃], (1) and (2), respectively. These isostructural compounds exhibit a monodimensional crystal structure formed by pillared double anionic chains with the formula [M(HPO₃)F₃]²⁻, extended along the [0 0 1] direction. These doubled ionic chains are the result of the linking of two simple chains in which there are alternating octahedral [MO₃F₃] and tetrahedral groups [HPO₃]. The ethylendiammonium cations are placed in the space delimited by three different chains. The metallic ions are interconnected by the pseudo-pyramidal (HPO₃)²⁻ phosphite oxoanions, adopting a slightly distorted octahedral geometry. The IR spectra show bands corresponding to the phosphite oxoanion and the ethylendiamonium cation at 2400 and 1600 cm⁻¹, respectively. The thermogravimetric analyses show that these phases are stable up to ca. 280 °C, at higher temperatures, the decomposition of the crystal structure begins by calcination of the organic cation and the elimination of the fluoride anions. The diffuse reflectance spectra show bands of the V³⁺ ion (d²) in octahedral symmetry. The values of the Dq (1540, 1540 cm⁻¹), and Racah parameters, B (560, 535 cm⁻¹) and C (3055, 3140 cm⁻¹) for (1) and (2), respectively, correspond with those usually found for octahedrically coordinated V(III) compounds. Magnetic measurements, performed on a powered sample from 5.0 to 300 K at 1000 G, in the ZFC and FC modes, indicate the existence of antiferromagnetic interactions.     

A2−αAα′BO4-type oxides as cathode materials for IT-SOFCs (A = Pr,Sm; A′ = Sr; B = Fe,Co)

Preparation, thermal expansion, electrical conductivity and polarization of A_2−αA _α′BO₄-type oxides (A = Pr, Sm, A′ = Sr, B = Fe, Co) were investigated systematically to evaluate their potential as cathode materials for IT-SOFCs. Within 0.8 ≤ α ≤ 1.5, A_2−αSr_αBO_4−δ (A = Pr, Sm, B = Fe, Co) could be obtained as a single K₂NiF₄-structural phase. Thermal expansion coefficients (TECs) of the specimens increase with increasing Sr²⁺ content, TECs of cobaltites are much higher than that of ferrites. The electrical conductivity of cobaltites is in the order of 10² S cm^− 1 near 800 °C, which is acceptable for the cathode of IT-SOFC. Polarization measurements showed that Sm_0.5Sr_1.5CoO_4−δ exhibited the lowest cathodic overpotential at 700–900 °C (72 mV at 500 mA/cm² at 800 °C), being a high potential candidate of cathode material for IT-SOFCs.     

Atomic oxygen adsorption on the silicon-doped hafnium carbide (0 0 1) surface from first principles

To improve the oxidation resistance of Hafnium carbide (HfC) surface, we investigated the adsorption of atomic oxygen on the silicon–doped HfC (0 0 1) surface by first principles. The O/HfC (0 0 1) system was also calculated for comparison. The (√2 × √2) R45° supercell was constructed to calculate the adsorption. In calculations, we treated the exchange and correlation potential with the revised version of the Perdew–Burke–Ernzerhof generalized-gradient approximation (GGA-RPBE). Our data demonstrate that the preference adsorption site for oxygen atom is the 4–fold hollow site on the silicon–doped HfC (0 0 1) surface. The oxygen on the silicon–doped surface receives more charges from silicon atoms than that in O/HfC (0 0 1) from carbon atoms. The Si–O bonds exhibit ionic and covalent characteristics, while the C–O bond exhibits primarily covalence. And the covalence of Si–Hf bonds is stronger than that of C–Hf bonds. The strong Si–O and Si–Hf bonds indicate the strong interactions of oxygen with the silicon–doped surface. The strong interactions can explain the possibility of improving the oxidation resistance of HfC surface via doping silicon.     

Selective recognition of Pr3 + based on fluorescence enhancement sensor

(E)-2-(1-(4-hydroxy-2-oxo-2H-chromen-3-yl)ethylidene)hydrazinecarbothioamide (L) has been used to detect trace amounts of praseodymium ion in acetonitrile–water solution (MeCN/H₂O) by fluorescence spectroscopy. The fluorescent probe undergoes fluorescent emission intensity enhancement upon binding to Pr^3 + ions in MeCN/H₂O (9/1:v/v) solution. The fluorescence enhancement of L is attributed to a 1:1 complex formation between L and Pr^3 +, which has been utilized as the basis for selective detection of Pr^3 +. The sensor can be applied to the quantification of praseodymium ion with a linear range of 1.6 × 10^? 7 to 1.0 × 10^? 5 M. The limit of detection was 8.3 × 10^? 8 M. The sensor exhibits high selectivity toward praseodymium ions in comparison with common metal ions. The proposed fluorescent sensor was successfully used for determination of Pr^3 + in water samples.     

Removal of fluoride from aqueous media by Fe3O4@Al(OH)3 magnetic nanoparticles

A novel magnetic nanosized adsorbent using hydrous aluminum oxide embedded with Fe₃O₄ nanoparticle (Fe₃O₄@Al(OH)₃ NPs), was prepared and applied to remove excessive fluoride from aqueous solution. This adsorbent combines the advantages of magnetic nanoparticle and hydrous aluminum oxide floc with magnetic separability and high affinity toward fluoride, which provides distinctive merits including easy preparation, high adsorption capacity, easy isolation from sample solutions by the application of an external magnetic field. The adsorption capacity calculated by Langmuir equation was 88.48 mg g^?1 at pH 6.5. Main factors affecting the removal of fluoride, such as solution pH, temperature, adsorption time, initial fluoride concentration and co-existing anions were investigated. The adsorption capacity increased with temperature and the kinetics followed a pseudo-second-order rate equation. The enthalpy change (ΔH⁰) and entropy change (ΔS⁰) was 6.836 kJ mol^?1 and 41.65 J mol^?1 K^?1, which substantiates the endothermic and spontaneous nature of the fluoride adsorption process. Furthermore, the residual concentration of fluoride using Fe₃O₄@Al(OH)₃ NPs as adsorbent could reach 0.3 mg L^?1 with an initial concentration of 20 mg L^?1, which met the standard of World Health Organization (WHO) norms for drinking water quality. All of the results suggested that the Fe₃O₄@Al(OH)₃ NPs with strong and specific affinity to fluoride could be excellent adsorbents for fluoride contaminated water treatment.     

LixPbII1−2xMIIIxO (M = Al,Fe): A new solid solution series related to yellow PbO

New series of oxides, Li_xPb_1−2xM_xO (M = Al, Fe), for 0<x≤0.33 adopting the yellow PbO structure have been synthesized by solid state reaction of Li₂CO₃, Pb(NO₃)₂ and Al₂O₃/FeC₂O₄·2H₂O in air at 650–680 °C. Optical absorption spectra reveal systematic increase/decrease of electronic band gap E_g for the Al/Fe members as compared to the parent yellow PbO. Partial deintercalation of lithium occurs under oxidative conditions (Br₂/CH₃CN) with both the series.     

The structure and spectroscopy of lanthanide(III) complexes with picolinic acid N-oxide in solution and in the solid state

The spectroscopic characteristics and the crystal structure of Eu(III) complex with picolinic acid N-oxide ligand, picNO, at room and liquid-nitrogen temperatures are discussed. Studies concerning the Eu(III) ion luminescence (intensity, luminescence lifetime measurements, and excitation spectra of the ⁵D₀ → ⁷F₀ transition) are presented. The selective excitation luminescence spectroscopy of Eu(III) in the range of the ⁵D₀ → ⁷F₀ transition is used for the study of Eu/picNO complexes in solution equilibria. In the crystal the complex molecules build the two-dimensional structures with additional Na⁺ cations and water molecules. This structure consists of edge-sharing chains of Na distorted octahedral, interconnected by Eu polyhedra (distorted square antiprisms). The ligand, pyridine-2-carboxylate-1-oxide, coordinates to the Eu(III) ion as an ionic bidentate chelate, forming the Na[Eu(picNO)₄] complex of six-membered chelate rings with the bite angles of ca. 70.5°. The complex is symmetrical; the Eu(III) ion is eight-coordinated.     

Chemical etching of InP (1 0 0) wafer based on a volcanic mineral water

We have successfully demonstrated that a solution of spa water [Tamagawa Spa water (TaSW):H₂O₂ = 1:1] etches InP (1 0 0) wafer. The TaSW is a colorless acidic liquid of pH ∼1.1. It contains a considerable amount of positive ions, such as H⁺, Al³⁺, and Ca²⁺. The Cl⁻, HSO₄²⁻, and SO₄²⁻ ions are the main anions. The TaSW-etchant system provides shiny flat surfaces on the etched bottoms. The spa-etchant system has reproducible etching rates and does not erode photoresist masks. The etching kinetics is reaction-rate limited. The spa-etchant system is also found to etch GaAs (1 0 0) wafer, but the etched surface is considerably roughened.     

Evolution characteristic of OH absorption in Mg (5 mol% in melt):LiNbO3 crystal with post-grown Li-poor vapor transport equilibration

We have measured OH absorption spectra of a 0.47-mm-thick Z-cut MgO (5 mol% in melt):LiNbO₃ crystal subjected to post-growth Li-poor vapor transport equilibration (VTE) treatments at 1100 °C for different durations ranging from zero to 395 h. These spectra allow the evolution of OH absorption characteristics with prolonged VTE to be followed. After 2 h of VTE process an additional absorption appears at 3483 cm^? 1. A transition regime that the original 3536 cm^? 1 and new 3483 cm^? 1 absorptions simultaneously appear exists within the VTE duration range of 2–16 h. In this regime, the 3536 cm^? 1 absorption becomes weak gradually and eventually disappears around 16 h while the 3483 cm^? 1 absorption increases remarkably with the prolonged VTE. The presence of transition regime gives a hint that the 3483 cm^? 1 absorption is due to the VTE-induced formation of a new center. Based upon the spectral features, we have suggested a simple three-layer (two on surface and one in the center of crystal plate) model to describe the depth profile of the photorefractive damage MgO concentration threshold in the crystal in the transition regime. A Li out-diffusion theory is suggested and correlated with the model. To support the Li out-diffusion theory, some additional experiments have been done. These include the depth profile characterization of VTE-induced Li₂O content reduction and the measurement of the surface Li₂O content as a function of the VTE duration. A quantitative analysis and discussion shows that the model is well supported by the experimental results.     

X-ray powder diffraction,vibration and thermal studies of [A0.92(NH4)0.08]2TeCl4Br2 with A = Cs,Rb: Influence of mixed cationic and anionic substitutions

The crystal structures of [A_0.92(NH₄)_0.08]₂TeCl₄Br₂ with A = Cs, Rb have been determined using X-ray powder diffraction techniques. The two compounds crystallize in the tetragonal space group P4/mnc, with the unit cell parameters: a = 7.452(1) Å, c = 10.544(3) Å, Z = 2 and a = 7.315(2) Å, c = 10.354(4) Å, Z = 2 in the presence of Cs and Rb, respectively. These two compounds have an antifluorite-type arrangement of NH₄⁺/Rb⁺/Cs⁺ and octahedral TeCl₄Br₂^2? anions. The stability of these structure is by ionic and hydrogen bonding contacts: A?Cl, A?Br and N–H?Cl, N–H?Br. The different vibrational modes of these powders were analysed by FTIR and Raman spectroscopic studies. A DTA/TGA experiment reveals one endothermic peak at 780 K implicating the decomposition of the sample. At low temperature, one endothermic peak in thermal behavior is detected at around 213 K by DSC experiment. This transition was confirmed by dielectric measurements.     

Synthesis,magnetic and Mössbauer study of ε-FexN (2 < x < 3) nanowires

Several micro meter long nanowires of ε-Fe_xN (2 < x < 3) are synthesized through a reduction nitridation method of Fe-NTA precursor formed by a hydrothermal method. The formation of pure iron nitride nanowires is confirmed by XRD. SEM analysis shows the porous nature of the iron nitride nanowires, which will enhance its suitability in catalysis. The field dependent magnetic behavior shows the ferromagnetic nature of the iron nitride nanowires. An appreciably good magnetization value (71 emu/g) and low coercivity (24 Oe) of the system makes it suitable for magnetic recording head applications. The room temperature Mössbauer study of the pristine nitride nanowires shows the existence of two iron sites corresponding to Fe (II) and Fe (III) indicating structural disorder.     

Magnetic and electrical behaviour of La0.67Ba0.33Mn1 − xFexO3 perovskites

(La_0.67Ba_0.33)Mn_1 ? xFe_xO₃ manganites compounds have been prepared by doping up to 20% of Fe at the Mn site. As previously reported in the literature paramagnetic (PM) to ferromagnetic (FM) phase transition has been observed in materials with low Fe doping (≤ 10%). In our x = 0 and x = 0.05 compounds the Curie temperature (T_C) is close to room temperature. Above 10% Fe amount, specimens exhibit a glass magnetic behaviour with a spin- or cluster-like freezing process that can be related to a loss of ferromagnetic double exchange interaction. Below 10% of Fe³⁺ doping electrical-resistivity measurement shows metal – semiconductor transition with a maximum peak of resistivity (ρ_max) at a temperature T_P close to T_C. Above 10% of Fe³⁺ doping amount the materials exhibit only semiconductor behaviour. Both T_C and T_P decrease with doping rates with an increasing difference in temperature (T_P being lower than T_C). Results are consistent with a reduction of the number of available hopping sites for the Mn e_g(↑) electron due to substitution of Mn³⁺ by Fe³⁺ that suppress the double exchange (DE) interactions.     

Glutamic acid containing supermacroporous poly(hydroxyethyl methacrylate) cryogel disks for UO22+ removal

Supermacroporous cryogel with an average pore size of 10–200 μm in diameter was prepared by cryopolymerization of N-methacryloyl-(l)-glutamic acid (MAGA) and 2-hydroxyethyl methacrylate (HEMA). The poly(HEMA–MAGA) cryogel was characterized by surface area measurements, FTIR, swelling studies, elemental analysis and SEM. The poly(HEMA–MAGA) cryogel had a specific surface area of 23.2 m²/g. The equilibrium swelling ratio of the cryogel is 9.68 g H₂O/g for poly(HEMA–MAGA) and 8.56 g H₂O/g cryogel for PHEMA. The poly(HEMA–MAGA) cryogel disks with a pore volume of 71.6% containing 878 μmol MAGA/g were used in the removal of UO₂²⁺ from aqueous solutions. Adsorption equilibrium of UO₂²⁺ was obtained in about 30 min. The adsorption of UO₂²⁺ ions onto the PHEMA cryogel disks was negligible (0.78 mg/g). The MAGA incorporation significantly increased the UO₂²⁺ adsorption capacity (92.5 mg/g). The adsorption process is found to be a function of pH of the UO₂²⁺ solution, with the optimum value being pH 6.0. Adsorption capacity of MAGA contained PHEMA based cryogel disks increased significantly with pH and then reached the maximum at pH 6.0. Consecutive adsorption and elution cycles showed the feasibility of repeated use for poly(HEMA–MAGA) cryogel disks.