Application of k0-based internal mono standard instrumental neutron activation analysis method method for composition analysis of stainless steel clad sample

The k₀-based internal mono standard instrumental neutron activation analysis (INAA) method was used for the composition analysis of some irregular shape stainless steel (SS) samples of type SS 316M, which is used as fuel cladding in Indian fast breeder test reactor (FBTR). The method utilizes in situ relative detection efficiency using γ-rays of the activation products present in the sample for overcoming γ-ray self-attenuation. Samples were neutron activated using the thermal column as well as the core position of the reactor and the assay of radioactivity was carried out by high-resolution gamma ray spectrometry. The elements determined were Fe, Cr, Ni, Mo, Mn, Co, Cu, As and W. Since all the major elements (Fe, Cr, Ni, Mo and Mn) were amenable to NAA, the relative elemental concentrations with respect to Fe, obtained by this method, were converted to their absolute values by mass balance. The results were compared with specified compositions and found to be satisfactory. In order to validate these results obtained by the standard-less approach, sub samples of SS 316M in solution forms were analyzed by prevalent relative and k₀ methods of INAA, and results were found to be in good agreement. The accuracy of the internal mono standard INAA method has been evaluated by analyzing an alloy steel certified reference material, CRM 225/1 of British Chemical Standards (BCS).     

Regioselective oxidation of N-alkylpyrrolidines to pyrrolidin-5-ones by RuCl3/NaIO4

RuCl₃/NaIO₄ under EtOAc/H₂O biphasic conditions, selectively oxidizes the Nα-endo-methylene group of pyrrolidine derivatives, without affecting the exo-methylene group adjacent to the N-heteroatom.     

Determination of thermodynamic properties of aqueous mixtures of MgCl2 and Mg(NO3)2 by the potentiometric method at T = 298.15

In this research, thermodynamic properties of the ternary electrolyte system (MgCl₂ + Mg(NO₃)₂ + H₂O) were investigated using a potentiometric method. The galvanic cell used had no liquid junction of type: Mg-ISE|MgCl₂ (m_A), Mg(NO₃)₂ (m_B), H₂O|Ag/AgCl. The measurements were performed at T = 298.15 K and at total ionic strengths from 0.001 to 8.000 mol/kg for different series of salt ratios r=mMgCl₂/mMg₂(NO₃) =1.00, 2.50, 5.00, 7.50, 10.00 and 15.00. The PVC based magnesium ion-selective electrode (Mg-ISE) and the Ag/AgCl electrode used in this work were prepared in our laboratory and showed a reasonably good Nernst response. The Pitzer ion interaction model and Harned rule were used to illustrate the ternary electrolyte system investigated. The experimental results showed that both Pitzer model and Harned rule were suitable to be used satisfactorily to describe this ternary system.     

Halogen-deuterium exchange reaction mediated by tributyltin hydride using THF-d8 as the deuterium source

A regioselective deuteration method for a wide variety of aromatic compounds using the halogen-deuterium exchange reaction initiated by Bu₃SnH using THF-d₈ as the deuterium source was developed.     

Structural transformation and oxidation of Sr2MnO3.5+x determined by in-situ neutron powder diffraction

The oxidation of the n = 1 Ruddlesden-Popper phase, Sr₂MnO_3.5+x, where 0 ≤ x ≤ 0.5 has been investigated using a combination of in-situ diffraction techniques. In agreement with previous reports the room temperature structure of Sr₂MnO_3.5+x was determined to be monoclinic crystallising in space group P2₁/c. On heating in air the material undergoes rapid oxidation at a relatively modest temperature, ∼275 °C. The oxidation process is coincident with a significant change in the structure, with the material now adopting a tetragonal I4/mmm structure. In the oxygen deficient phase where x > 0 the Mn coordination is square pyramidal, with a sixth partially occupied oxygen position giving rise to octahedral coordination. Oxidation of Sr₂MnO_3.5+x results in the filling of the partially occupied O4 positions and a resulting increase in symmetry, with the Mn coordination now adopting solely a distorted octahedral environment.     

Evolution of structure and magnetic properties in electron-doped double perovskites, Sr2−xLaxMnWO6 (0?x?1)

Powder neutron and X-ray diffraction studies show that the double perovskites in the region 0?x?1 exhibit two crystallographic modifications at room temperature: monoclinic P2₁/n and tetragonal I4/m, with a boundary at 0.75<x<0.9. Magnetic susceptibility measurements indicate that for x=0 and 0.5 Sr_2−xLa_xMnWO₆ orders antiferromagnetically (AFM) at 15 and 25 K, respectively, for 0.75?x<1.0, a contribution of weak ferromagnetism (FM), probably due to canted-AFM order, increases with increasing x. The end point compound SrLaMnWO₆ shows the strongest FM cluster effect; however, no clear evidence of magnetic order is discernable down to 4.2 K. X-ray absorption spectroscopy (XAS) confirms Mn²⁺ and mixed-valent W^6+/5+ formal oxidation states in Sr_2−xLa_xMnWO₆.     

The Crystal Chemistry of Lithium in the Alluaudite Structure: A Study of the (Na1−xLix)CdIn2(PO4)3 Solid Solution (x=0 to 1)

Several compounds of the (Na_1−xLi_x)CdIn₂(PO₄)₃ solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x=0.00, 0.25, and 0.50. X-ray Rietveld refinements indicate the occurrence of Cd²⁺ in the M(1) site, and of In³⁺ in the M(2) site of the alluaudite structure. This non-disordered cationic distribution is confirmed by the sharpness of the infrared absorption bands. The distribution of Na⁺ and Li⁺ on the A(1) and A(2)′ crystallographic sites cannot be accurately assessed by the Rietvled method, probably because the electronic densities involved in the Na⁺→Li⁺ substitution are very small. A comparison with the synthetic alluaudite-like compounds, (Na_1−xLi_x)MnFe₂(PO₄)₃, indicates the influence of the cations occupying the M(1) and M(2) sites on the coordination polyhedra morphologies of the A(1) and A(2)′ crystallographic sites.     

The synthesis mechanism of Ca3Al2O6 from soft mechanochemically activated precursors studied by time-resolved neutron diffraction up to 1000°C

The reaction pathway for the Ca₃Al₂O₆ formation up to 1300°C, from mechanochemically treated mixtures of amorphous aluminum hydroxide and CaCO₃, was studied in situ by differential thermal analysis, constant heating rate dilatometry and time-resolved neutron powder diffraction. The experiment was carried out, in an open system, on a sample with the nominal Ca₃Al₂O₆ stoichiometry. The results obtained by neutron diffractometry and thermal analysis were in good agreement with the data obtained by scanning electron microscopy and X-ray diffraction on heat-treated and-quenched samples. The synthesis path implied the formation of cryptocrystalline Al₂O₃, crystalline CaO, CaAl₂O₄ and Ca₁₂Al₁₄O₃₃ as transitory phases. Finally the nucleation and growth of the single phase Ca₃Al₂O₆ took place at 1300°C and exhibited porous structure due to CO₂ and H₂O release.     

Synthesis and characterization of metal substituted AlxCr1−x(acetylacetonate)3 single-source precursors for their application to MOCVD of thin films

A detailed study, involving the synthesis of a single-source precursor containing two metal ions sharing the same crystallographic site, has been undertaken to elucidate the use of such a single-source precursor in a CVD process for growing thin films of oxides comprising these two metals, ensuring a uniform composition and distribution of metal ions. The substituted complexes Cr_1−xAl_x(acac)₃, where acac = acetylacetonate, have been prepared by a co-synthesis method, and characterized using UV–Vis spectroscopy, TGA/DTA measurements, and single crystal X-ray diffraction at low temperature. All the studied compositions crystallize in the monoclinic space group P2₁/c with Z = 4 in the unit cell. It was observed that the ratio (Al:Cr) of the site occupancy for the metal ions, obtained from single crystal refinement, is in agreement with the results obtained from complexometric titrations. All the solid state structures have the metal in an octahedral environment forming six-membered chelate rings. M–O acac bond lengths and disorder in the terminal carbon have been studied in detail for these substituted metal–organic complexes. One composition among these was chosen to evaluate their suitability as a single-source precursor in a LPMOCVD process (low-pressure metal–organic chemical vapour deposition) for the deposition of a substituted binary metal oxide thin film. The resulting thin films were characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy.     

A novel route to synthesize cubic ZrW2−xMoxO8 (x=0-1.3) solid solutions and their negative thermal expansion properties

Cubic ZrW_2−xMo_xO₈ (c-ZrW_2−xMo_xO₈) (x=0-1.3) solid solutions were prepared by a novel polymorphous precursor transition route. X-ray diffraction (XRD) analysis reveals that the solid solutions are single phase with α- and β-ZrW₂O₈ structure for 0?x?0.8 and 0.9?x?1.3, respectively. The optimum synthesis conditions of ZrWMoO₈ are obtained from differential scanning calorimetry-thermal gravimetric analysis (DSC-TGA), XRD and mass loss-temperature/time curves. Following the above experience, the stoichiometric solid solutions of c-ZrW_2−xMo_xO₈ (x=0-1) are obtained within 1 wt% of mass loss. The relationships of lattice parameters (a), phase transition temperatures (T_c) and instantaneous coefficients of thermal expansion (α_i) against the content x of Mo are discussed based on the variation of order degree parameters of ZrW_2−xMo_xO₈.     

Enantioselective addition of diethylzinc to aromatic aldehydes catalyzed by Ti(IV) complexes of C2-symmetrical chiral BINOL derivatives

Enantioselective addition of diethylzinc to a series of aromatic aldehydes is developed using new chiral C₂-symmetric ligand (S)-2,2′-(1,1′-binaphthyl-2,2′-diylbis(oxy))bis(methylene)bis(4-nitrophenol) (S)-2b. The catalytic system employing 10 mol % of (S)-2b and 120 mol % of Ti(OiPr)₄ was found to promote the addition of diethylzinc to a wide range of aromatic aldehydes with electron-donating and electron-withdrawing substituents, giving up to 89% ee and up to 95% yield of the corresponding secondary alcohol under mild conditions.     

Neutron diffraction study of the crystal structure and structural phase transition of La0.7Ca0.3−xSrxCrO3 (0≤x≤0.3): The relationship between thermodynamic behavior and crystal structure changes at the phase transition

The crystal structure of the La_0.7Ca_0.3−xSr_xCrO₃ series, including the compositional and temperature dependence of the structural parameters, has been studied by variable temperature neutron diffraction measurements. The extent of the distortions from the ideal cubic perovskite structure has been evaluated quantitatively using the average bond lengths and the mean volumes of the [CrO₆] octahedron and [(La/Ca/Sr)O₁₂] polyhedron, and has been shown to decrease with increase of Sr content or temperature. At the structural phase transition from the orthorhombic (Pnma) structure to the rhombohedral one, the volume of the [CrO₆] octahedron decreases whereas that of the [(La/Ca/Sr)O₁₂] polyhedron shows little difference, resulting in an overall decrease in the level of distortion. The change in the degree of distortion at the phase transition decreases with increase of Sr content, in agreement with the smaller variation of the enthalpy and volume for the specimens with higher Sr content.     

A DFT study of lithium battery materials: application to the β-VOXO4 systems (X=P, As, S)

VOXO₄ systems have been considered as potential lithium battery electrodes. They mainly present two distinct structural types: the tetragonal “α” type with a two-dimensional framework, and the three-dimensional orthorhombic “β”. DFT calculations were performed on this latter system for several β-Li_xVOXO₄ compounds (x=0, 1; X=P, As, S). They allowed to propose structural models for VOAsO₄ and LiVOSO₄, not fully crystallographically well described yet. Based on an experimental model of two-phase processes, these calculations led also to a good simulation of electrochemical potential values. A density of states analysis put in evidence the “inductive effect” and the role played by (XO₄)ⁿ⁻ groups inside the host frameworks on these potentials.     

Convenient synthesis of Pt(0) olefin complexes by colorimetric reduction of Pt(II) complexes with SmI2

Homoleptic olefin platinum(0) complexes, Pt(C₇H₁₀)₃ and Pt(cod)₂, were synthesized by the colorimetric reduction of platinum(II) complexes with SmI₂ in the presence of 2-norbornene or COD. This is a practically more convenient method for the synthesis of the Pt(0) complexes than the literature method employing Li₂(cot).     

The nonclassical noncovalent interactions control: A case study of the crystal structure of 3,5-dibromo-2-amino-4,6-dimethylpyridinium tetrahalocuprate [3,5-DBr-2-A-4,6-DMPH]2CuX4 (X = Cl, and Br)

The compound [3,5-dibromo-2-amino-4,6-dimethylpyridinium]₂CuCl₄, (1), was prepared from acidic hydrochloric acetonitrilic medium containing CuCl₂ and 3,5-dibromo-2-amino-4,6-dimethylpyridinium bromide while [3,5-dibromo-2-amino-4,6-dimethylpyridinium]₂CuBr₄, (2), from acidic HBr/Br₂ ethanolic medium containing 4,6-dimethylpyridine and CuBr₂. The ring got dibrominated at 3 and 5 positions in situ. Single-crystal X-ray diffraction proved the compounds to be isomorphous in P − 1. A systematic study of the crystallographic parameters in dibrominated and nonbrominated 2-amino-4,6-dimethylpyridine salts will explain the role of nonclassical noncovalent interaction between aryl bromine and ionic metal bromide in the control of structure.     

Phase transitions in A-site substituted perovskite compounds: The (Ca1-2xNaxLax)TiO3 (0?x?0.5) solid solution

The (Ca_1-2xNa_xLa_x)TiO₃ (0?x?0.5) A-site substituted perovskite compounds have been synthesized and characterized by XRD and Raman spectroscopy at room temperature. The XRD powder diffraction study suggests that the end-member Na_1/2La_1/2TiO₃ crystallizes in the tetragonal space group I4/mcm. The phase transition from Pbnm to I4/mcm is located between x=0.34 and 0.39 and is driven by the variation of ionic radii at the A-site. The observed Raman modes are in agreement with group theory analysis, and the relationships between the behavior of structural parameters (e.g. Ti-O-Ti bond angle), indicated by long-range order, and the corresponding Raman frequency shifts and intensity evolution, indicated by short-range order, are established and discussed in terms of the radius effect and the mass effect.     

Investigation of modification of hydrogenation and structural properties of LaNi5 intermetallic compound induced by substitution of Ni by Pd

The hydrogenation properties of the LaNi₅ (CaCu₅ type, hP6, P6/mmm) and Pd substituted derivatives LaNi_5−xPd_x compounds have been studied in the whole homogeneity range of the solid solution (0.25≤x≤1.5). The pressure versus hydrogen content isotherms show several plateaus and an increase of the plateau pressure as a function of palladium concentration. The volume increase of the Pd substituted alloys should have resulted in a lowering, and not an increase, of the plateau pressure, according to the conventional models based on the size effect. In order to elucidate the origin of this anomalous behavior, both an experimental and a theoretical ab initio electronic structure investigation have been carried out. Experimentally, the nature and the structural properties of the hydrides have been studied by both in situ and ex situ neutron diffraction. The crystal structures of the three hydride phases are reported (LaNi_3.5Pd_1.5D_1.96, filled-up CaCu₅ type, P6/mmm; LaNi₄PdD_2.72, LaNi₂(Ni_0.75Pt_0.25)₃H_2.61 type, oI128, Ibam; LaNi_4.75Pd_0.25D_5.67, partly ordered CaCu₅ type, P6mm). In addition, the phase diagram of LaNi_5−xPd_x-H system has been investigated. The electronic and thermodynamic properties of both intermetallic compounds and the hydrides have been studied by ab initio electronic structure calculations. The theoretical results are in good agreement with our experimental data, and show that electronic interactions play a major role in the hydrogenation behavior of these Pd substituted intermetallic compounds, and that these effects cannot be accounted for by a simplistic model based on the size effect alone.     

Synthesis of new CO2-soluble ruthenium(II) and cobalt(II) polypyridine complexes bearing fluorinated alkyl chains and their application to photoreduction of liq. CO2

Eight types of new CO₂-soluble or CO₂-philic ruthenium(II) and cobalt(II) polypyridine complexes, namely, [M(F84OPh)₃](BArF)₂, [M(F44OPh)₃](BArF)₂, [M(F62Ph)₃](BArF)₂, and [M(F62O)₃](BArF)₂ (M = Ru or Co, BArF: tetrakis[3,5-bis(trifluoromethyl)phenyl]borate), were prepared from bipyridine derivatives bearing highly fluorinated alkyl chains and applied to the photoreduction of liq. CO₂ under a high pressure of 6.8 MPa at 35 °C. All these complexes have higher philicity toward liq. CO₂ than the corresponding complexes with PF⁶⁻ as the counteranion. Using the Ru(II)-Co(II) systems of [M(F44OPh)₃](BArF)₂ and [M(F62O)₃](BArF)₂, direct photoreduction of CO₂ was achieved without the use of any organic solvent.     

Crystal structure, characterization and thermoelectric properties of the type-I clathrate Ba8−ySryAl14Si32 (0.6≤y≤1.3) prepared by aluminum flux

The title compound was prepared as single crystals using an aluminum flux technique. Single crystal and powder X-ray diffraction indicate that this composition crystallizes in the clathrate type-I structure, space group Pm3?n. Electron microprobe characterization indicates the composition to be Ba_8−ySr_yAl_14.2(2)Si_31.8(2) (0.77<y<1.3). Single-crystal X-ray diffraction data (90 and 12 K) were refined with the Al content fixed at the microprobe value (12 K data: R₁=0.0233, wR₂=0.0441) on a crystal of compositions Ba. The Sr atom preferentially occupies the 2a position; mixed Al/Si occupancy was found on all framework sites. These refinements are consistent with a fully occupied framework and nearly fully occupied cation guest sites as found by microprobe analysis. Temperature dependent electrical resistivity and thermal conductivity have been measured from room temperature to 1200 K on a hot-pressed pellet. Electrical resistivity reveals metallic behavior. The negative Seebeck coefficient indicates transport processes dominated by electrons as carriers. Thermal conductivity is between 22 and 25 mW/cm K. The sample shows n-type conductivity with a maximum figure of merit, zT of 0.3 at 1200 K. A single parabolic band model predicts a five-fold increase in zT at 800 K if carrier concentration is lowered.