Hyperfine characterization of tin-doped indium sesquioxide

The hyperfine interactions at In and Sn sites of In₂O₃Sn (ITO) were measured through time-differential perturbed angular correlations and Mössbauer spectroscopy, respectively. Polycrystalline samples prepared by co-precipitation with nominal 0.025, 1 and 5 at.% Sn were studied. They all showed the cubic bixbyite structure characteristic of In₂O₃ after annealings at 200 °C. The quadrupole interaction at In sites appears nearly independent of Sn concentration being the main result of the presence of Sn in the lattice, the gradual disappearence of the dynamic perturbation caused by after-effects. The Mössbauer data demonstrate that Sn ions are in a 4+ state with Q=0.60₆ mm/s and=0.22₆ mm/s relative to SnO₃Ca at room temperature.     

Considering uncertainty of measurement when assessing compliance or non-compliance with reference values given in compositional specifications and statutory limits: a proposal

Considering the uncertainty of measurement (UOM) is mandatory when assessing compliance with reference values given in compositional specifications and statutory limits, but the matter is still open to question. Working in the signal or concentration domains and considering false negative together with false positive errors are the main points of debate. Frequently, the available approaches look too simplified for being accurate or too complex (since more rigorously formulated from a theoretical point of view) for being largely acceptable. In the Authors opinion, assessing compliance with reference values given in compositional specifications and statutory limits is a problem similar to that of estimating the limit of detection. This allows proposing a simple operational approach based on well-known and accepted assumptions and approximations. This proposal, described in the light of the most recent literature information, is aimed to stimulate a critical discussion in view of evaluating possible corrections to the generally accepted approach.Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher.     

Study of the evolution of the hyperfine parameters in nanostructured Fe–Mn–Cu system

An unusually large attenuation (approximately 50%) in the low temperature nuclear orientation directional gamma anisotropy from unannealed thermal neutron irradiated single crystal (¹⁶⁰Tb)TbNiAl₄ has been observed in the region of saturation of the second order nuclear orientation coefficient, B₂. It is suggested that the form of the remanent neutron activation recoil damage in unannealed (¹⁶⁰Tb)TbNiAl₄ is fundamentally electric quadrupolar in origin, as opposed to magnetic dipolar.     

Solvent effect as the result of frontier molecular orbital interaction-1 : The diels-alder reaction between 1,4-naphthoquinone and 2,3-dimethylbutadiene

A kinetic investigation of the solvent effect in the Diels-Alder reaction of2,3-dimethylbutadiene and 1,4-naphthoquinone was undertaken and a hyperbolic correlation was obtained with the Acceptor Numbers (AN) of the solvent. Since ANs correlate with the LUMO of the solvent, the results can be rationalized in terms of an interaction between the LUMO of the solvent and the HOMO of the quinone which determines the MO energy of the solvated quinone. This rationalization seems useful when reactants, products and transition state are weakly polar.     

Mössbauer Investigation of Fe–Mn–Cu Nanostructured Alloys Obtained by Ball Milling

Fe₇₉Mn₂₁, (Fe₇₉Mn₂₁)₉₀Cu₁₀, and (Fe₇₉Mn₂₁)₈₀Cu₂₀, alloys, prepared by high energy ball milling were characterized by Mössbauer spectroscopy, X-ray diffraction and ac-susceptibility. Results indicate that the Cu addition favors the formation of a FCC phase with two different magnetic states at room temperature, i.e., an antiferromagnetic and a paramagnetic one. Thermal evolution of the Mössbauer spectra revealed the occurrence of a magnetic ordering along a wide temperature range. This behavior is probably related to Fe atoms in FCC-Fe(Mn,Cu) phase having different environments and grain size distribution. Thermal dependence of in-phase ac-susceptibility shows that a long range ordering starts at 240 K for the Fe₇₉Mn₂₁ alloy and shifts towards lower temperatures with the Cu content. These results would reflect a long-range magnetic ordering transition with a distribution of ordering temperatures rather than a blocking process of particle single-domains.     

Study of the magnetic and electronic properties of the Fe4N with pressure

In the present work, we report ab-initio studies of the magnetic property variations with pressure of both iron sites in the structure of Fe₄N, using full-potential linearized augmented plane wave method and the Perdew–Burke–Ernzerhof functional and generalized gradient approximation to describe the exchange-correlation potential are reported. The results show that the magnetic moment of FeI is almost constant while the magnetic moment of FeII presents a discontinuity when the lattice parameter is varied. This is reflected in the compression of the spin up and down energy bands to different concentration points. The variation in the FeII magnetization arises mainly from changes in the d_xy, d_xz, d_yz and d_x2−y2 orbitals.     

Formation of Mn-doped iron silicides by ball milling

Using X-ray diffraction (XRD) and Mössbauer spectroscopy, we have studied the sequence of phase formations in the solid Mn-doped iron silicide series Fe_1?x Mn _x Si₂, with 0.00? ≤ ?x? ≤? 0.12, in samples prepared by mechanical alloying from the pure elements. The milling was carried out at room temperature in Ar atmosphere in a horizontal mill for 15 h. The XRD patterns display broad lines, which can be ascribed to stable and metastable iron silicides like β-FeSi₂, ?-FeSi, α-FeSi₂, MnSi, and Si. The set of hyperfine parameters obtained support the coexistence of β-FeSi₂, α-FeSi₂ and ?-FeSi, in agreement with the XRD results. No replacement of Fe by Mn atoms in the regular sites of β-FeSi₂ has been observed.     

Mössbauer Spectroscopy, Dilatometry and Neutron Diffraction Detection of the ɛ-Phase Fraction in Fe–Mn Shape Memory Alloys

The results of a Mössbauer spectroscopy (MS) and a neutron diffraction (ND) study carried out on a set of Fe–Mn alloys quenched from high temperatures are reported. Upon quenching the high temperature stable phase FCC (γ) together with metastably retained HCP-(?) phase are formed. The lattice parameters obtained using ND are in excellent agreement with previous results of the literature. The phase fractions obtained from MS are coincident, within experimental errors, with those extracted from ND, with exception of the case of an alloy with the lowest Mn content (16.8 at.% Mn). That situation can be associated with the occurrence of a high density of stacking faults (SF) in the γ phase or to the presence of a paramagnetic γ phase. ? phase fractions obtained from MS and ND decrease smoothly with Mn content but are always larger than the values reported in literature resulting from dilatometry.     

Heterodiene syntheses—XIX: Correlation of the kinetic data with lumo energies in the reaction between 1-aryl-4-benzylidene-5-pyrazolones and isopropyl vinyl ether

The kinetics of the reaction between 1-p-substituted phenyl-4-benzylidene-5-pyrazolones and isopropyl vinyl ether have been studied by quantitative spectroscopic analysis and liquid chromatography. The rate increases with the electron attracting character of the substituents and a correlation is obtained with σ- constants. The polarographic one-electron half-wave reduction potentials E^red_{$\text{1}\text{2}$}, which represent an experimental measure for the relative energy of the lowest unoccupied molecular orbital (LUMO), were measured. Good correlations were obtained between these and the kinetic data, thus demonstrating the frontier-controlled character of the cycloaddition and the dominant interaction between the LUMO of the pyrazolone and the highest occupied molecular orbital (HOMO) of the vinyl ether.     

Comparing some operational approaches to the limit of detection

The limit of detection is one of the fundamental metrological characteristics of any chemical measurement systems but, even now, it is a highly controversial matter because of the existing differences in terminology, formulations and understanding. Even when limiting the analysis to those operational approaches that, because of their simplicity, are often suggested by the guidelines of some international bodies, the available approaches can return appreciably different estimates. In this paper, the matter is critically reconsidered, and the different approaches compared with the aid of some case studies.