Mössbauer spectroscopy in the investigation of new mineral–related materials

New materials based on the composition of the mineral schafarzikite, FeSb $_{2}\textit {O}_{4}$ , have been synthesised. $^{57}$ Fe- and $^{121}$ Sb- Mössbauer spectroscopy shows that iron is present as Fe $^{2+}$ and that antimony is present as Sb $^{3+}$ . The presence of Pb $^{2+}$ on the antimony sites in materials of composition FeSb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ induces partial oxidation of Fe $^{2+}_{}$ to Fe $^{3+}$ . The quasi-one-dimensional magnetic structure of schafarzikite is retained in FeSb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ and gives rise to weakly coupled non-magnetic Fe $^{2+}$ ions coexisting with Fe $^{3+}$ ions in a magnetically ordered state. A similar model can be applied to account for the spectra recorded from the compound Co $_{0.5}$ Fe $_{0.5}$ Sb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ .     

MA-XRF study of 15th–17th century icons from the collection of the National Museum in Krakow,Poland

In 2015, the National Museum in Krakow, Poland, started a grant from the National Programme for the Development of Humanities, its goal to investigate an important collection of old Orthodox painting, including more than 50 15th to 17th century icons originating from the territory of the historical Orthodox Diocese of Przemyśl within the borders of the Polish Kingdom. The aim of researching the iconography, provenance, and technology of the artworks was to describe their specific features and destination, in detail, and to characterise their artistic milieu. Many different techniques were used during research, such as X-ray fluorescence (XRF), X-ray diffraction, reflectography, radiography, ultraviolet–visible imaging, Fourier-transform infrared spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy of prepared paint layer cross sections, and dendro-chronological analysis. This paper focuses on highlighting the advantages and disadvantages of the spatially resolved macro-XRF scanning (MA-XRF) technique. Most interesting results concluded from elemental distribution maps obtained through the use of Bruker, M6 Jetstream MA-XRF scanner include the following: characterisation of the type of gold and silver foil used in the icons; determination of main pigments, including the use of lead tin yellow unusual in iconography; and the noting of an interesting distribution of blue pigments as well as the presence of orpiment. Surprisingly, a considerable amount of zinc with azurite addition was observed in brown layers. The results obtained primarily highlight all the typical features of local Carpathian icon craft.     

Mössbauer effect and X-ray diffraction investigation of Si–Fe thin films

An X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy investigation of Si_{100– x} Fe _x (0?<?x?<?80) thin films prepared by combinatorial sputtering methods is reported. Resulting Mössbauer spectra were fit to Voigt-based distributions of quadrupole doublets for paramagnetic spectral components and Zeeman split sextets for ferromagnetic spectral components. In conjunction with the X-ray measurements, these results show that the Si-rich films are a mixture of dilute Fe in amorphous Si and an approximately equiatomic amorphous SiFe phase. Fe-rich films show the presence of a ferromagnetically ordered phase. For x?<?73, this ferromagnetic phase is amorphous or nanostructured and for x?≥?73, the phase is shown to be a crystalline bcc phase. Results are discussed in terms of short-range structural ordering in these alloys.     

Structural and Mössbauer studies of aerosol FeCu nanoparticles in a wide composition range

Structure and magnetic state of aerosol FeCu nanoparticles of 10–30 nm size with Cu content of 0.6–92.1 at.% have been examined by X-ray diffraction and Mössbauer spectroscopy. The FeCu particles have been shown to consist of an iron core surrounded by a copper and Fe oxide shell. With increasing Cu content the iron core having a bcc structure is reduced down to its complete disappearance followed by vanishing ferromagnetism of the particles. Within the copper content from 4.9 to 74.3 at.% the bcc and fcc phases coexist, with the fcc phase having a lattice constant close to that of pure copper and the bcc lattice constant being slightly higher than that for pure Fe due to embedding Cu atoms into the Fe lattice. At Fe-rich FeCu samples a presence of two-spin (ferromagnetic and paramagnetic) components of the fcc Fe is also observed. In the case of a thin copper shell there is only the ferromagnetic fcc Fe, whereas with further thickening of the shell both spin states of the fcc Fe appear existing up to a 20% Cu content. For FeCu samples with a higher Cu content they disappear due to oxidation of the copper grains. The Cu-rich samples with Cu content higher 80 at.% have a fcc structure, with the lattice constant being slightly higher than that of copper and they are paramagnetic. A slight increase of the lattice constant is due to the penetration of small iron aggregations into the Cu grains. In contact with air, the FeCu particles become covered with Fe₃O₄ and Cu₂O. Their long-term exposure to ambient conditions leads to further oxidation process of Cu₂O to CuO.     

The investigation of magnetic state variations in α-Fe and its alloys by means of continuous temperature scanning of the Mössbauer effect

A new method for continuous temperature scanning of the Mössbauer effect was developed permitting the measurement in a broad temperature range with satisfactory precision. The temperature dependence of Mössbauer radiation transmission for -Fe, amorphous Fe-P and for alloys was measured from 20–800°C. A region of anomalous transmission was observed for crystalline -Fe and its alloys and a new method of Debye-temperature determination was proposed.     

Spreading of gallium on the surface of a contact layer of variable composition from the Pb–Bi system

An approach for obtaining substrates of variable composition of metal systems is proposed. The spreading of drops of gallium of uniform size on the surfaces of areas of variable composition, obtained via contact melting of the Bi-Pb system is studied. A change in the diameter of a spot is observed, depending on the position of the drop on the surface of the substrate. A change in the shape of the spot is observed, depending on the composition along the interface region. The need to use force to separate the crystallized drops from the surface of the substrate, depending on the positions of the gallium drops (i.e., the substrate’s composition) confirms the wettability upon spreading.     

Mössbauer investigation of the reaction of ferrate(VI) with sulfamethoxazole and aniline in alkaline medium

Mechanisms on the oxidation of sulfamethoxazole (SMX) and aniline by ferrate(VI) (Fe^VIO $_{4}{^{2-}}$ , Fe(VI)) in alkaline medium suggested the formation of Fe(VI)-SMX or Fe(VI)-aniline intermediates, respectively. Fe(V) and Fe(IV) as other intermediate iron species have also been proposed in the mechanism. In this paper, rapid freeze Mössbauer spectroscopy was applied in rapidly frozen samples to explore intermediate iron species in the reactions of SMX and aniline with Fe(VI). In both reactions, Fe(VI)-SMX and Fe(VI)-aniline intermediates were not seen in second-minute time scale. Fe(V) and Fe(IV) were also not observed. Fe(III) was the only final species of the reactions.     

The structure and composition of novel electrodeposited Sn–Fe and Sn–Co–Fe alloys from a flow circulation cell system

This study involved the use of a flow circulation cell, using varying circulation rates as a room temperature process (20°C). Mössbauer and XRD analysis were conducted to ascertain whether amorphous or microcrystalline structures could be obtained at 20°C using a range of current densities. Amorphous or microcrystalline structures of Sn–Fe and Sn–Co–Fe have potentially important industrial applications for energy efficient cells, for use as high performance electrodes in lithium batteries, as environmentally acceptable corrosion resistant materials and are derived from an energy efficient environmentally friendly electrolyte process which would be acceptable as an industrial process. $^{\it 57}Fe$ and $^{\it 119}Sn$ Mössbauer investigations supported by XRD analysis confirmed that the room temperature flow circulation cell gave rise to previously unknown non-equilibrium amorphous structures which do not occur in the corresponding thermally prepared alloys as shown in the thermal equilibrium diagrams. Mössbauer analysis shows these alloys to be both amorphous and ferromagnetic. It is shown that the flow circulation cell used at 20°C based on the environmentally friendly gluconate bath reported gives amorphous based Sn–Fe and Sn–Co–Fe alloys over a useful range of current densities facilitated by using a range of circulation rates.     

155Gd Mössbauer investigation of the magnetic order and spin-reorientation in Gd3Ag4Sn4

In a recent study of the magnetic order in Gd₃Ag₄Sn₄ by neutron powder diffraction and ¹¹⁹Sn Mössbauer Spectroscopy we showed that both the Gd(2d) and Gd(4e) sublattices order antiferromagnetically at 28.8(2) K. We also demonstrated that the ‘magnetic event’ around 8 K is in fact a ‘plane to axis’ spin-reorientation of the Gd magnetic structure. Here, we extend our study with ¹⁵⁵Gd Mössbauer Spectroscopy. The initial magnetic ordering at 30(2) K is clear for both sites and substantial changes in the hyperfine fields are observed at 8 K when the magnetic structure reorients.     

The investigation of soliton solutions and conservation laws to the coupled generalized Schrödinger–Boussinesq system

This paper employed the principle of undetermined coefficients and Bernoulli sub-ODE methods to acquire the topological, non-topological, periodic wave and algebraic solutions of the coupled generalized Schrödinger–Boussinesq system (CGSBs). The concept of Lie point symmetry is applied to derive the point symmetries of the CSGE. The problem on nonlinear self-adjointness of the CSGE has not been solved in previous time. In the present paper, we solve this problem and find an explicit form of the differential substitution providing the nonlinear self-adjointness. Then we use this fact to construct a set of conserved vectors using the classical symmetries admitted by the equation and the general conservation laws (Cls) theorem presented by Ibragimov. Numerical simulation of the obtained results are analyzed with interesting figures showing the physical meaning of the solutions.     

Metastable compositionally and magnetically modulated state of Fe-Ni Invar and the associated super-moment dynamics from Mössbauer spectroscopy

The presence of magnetic and chemical clustering, in Fe₆₅Ni₃₅ Invar, had previously been inferred from various measurements which we review. We independently confirm both types of clustering and measure the associated supermoment dynamics for the first time. The temperature dependence of the fluctuation frequency is understood in terms of inter-cluster surface exchange energy and leads to a spherical cluster radius of 7.2 Å. The observed super-moment excitations are sufficient to explain the anomalous temperature dependence of the magnetization and are slow enough, compared to lattice response times, to cause the magnetovolume anomalies. The magnetic clusters are seen to persist far above T_c - at least up to 600 K. Using a two-cluster-type approximation, the mean compositional morphology is obtained as: 39 at% Fe₈₅Ni₁₅/61 at% Fe₅₃Ni₄₇. Also, the alloy which is most often referred to as “Invar”, is found to contain ⪅ 2 at% of α-Fe precipitate. A change of + 1 at% in the amount of this precipitate is found to cause a change of ≃ + 50 K in the T_c measured on first heating. The three most common models for Invar - itinerate model, two γ-state model, and mixed exchange model - are discussed in terms of both data available in the literature and our own results. The mixed exchange approach is shown to be the most reasonable. Its crudeness is argued to arise from two factors: (i) since detailed structural data were not available, it has assumed the wrong fine scale schemical morphology, and (ii) it uses only three values of J_ij whereas we expect a broad distribution of exchange energies to arise from a Slater-Bethe-Bozorth-type interaction whose strength is a function of local composition.     

Study of defects in Fe–Re and Fe–Mo alloys by the Mössbauer and positron annihilation spectroscopies

The room temperature positron annihilation lifetime spectra and ⁵⁷Fe Mössbauer spectra were measured for pure Fe as well as for iron-based Fe_1?xRe_x and Fe_1?xMo_x solid solutions with x in the range 0.01≤x≤0.05. The measurements were performed in order to learn more about creation of structural defects during formation and further mechanical processing of the iron systems under consideration. The spectra were collected at least twice for each studied sample synthesized in an arc furnace—after cold rolling to the thickness of about 40 μm as well as after subsequent annealing at 1270 K for 2 h. It was found that in the annealed samples positrons live much shorter than in the not annealed ones which suggest that the latter samples are more defected as it could be expected. Moreover simultaneous analysis of the positron and Mössbauer data shows that cold rolling leads to creation of two types of defects. It seems that they are dislocations and vacancies. Finally from the Mössbauer data it follows that vacancies are located mainly in the vicinity of non-iron atoms, Re or Mo. This speaks in favour of the suggestion that in iron matrix the impurities mentioned above and vacancies interact attractively which supports the known from the literature, theoretical calculations on the Mo-vacancy interaction in iron.     

Effect of alloying on the stabilities and catalytic properties of Pt–Au bimetallic subnanoclusters: a theoretical investigation

Density functional theory (DFT) has been applied to study the geometrical and electronic structures and the catalytic properties for NO oxidation of pure Pt and PtAu clusters. The calculated results suggest that Pt₁₀ clusters shows the most stable structure among the pure Pt _n (n = 2–13) clusters with the local maximum Δ₂ E value. The doping of Au atoms reduces the stability of the clusters, and Pt₆Au₄ cluster has the most stable structure among Pt_10?n Au _n (n = 1–7) clusters, due to the closest band centers between Pt and Au atoms (0.83 eV) and the obvious s–p resonance peaks near the Fermi level. Pt₆Au₄ cluster displays the strongest activation of O₂ molecules among Pt_10?n Au _n (n = 0–7) clusters, owing to the clear overlap between O 2p and Pt 6 s and Au 6 s near the Fermi level, and the more positive d band center than the others. The interaction between NO and metals changes slightly in NO/Pt_10-nAu_n (n = 2–7) systems, which is weaker than that in NO/Pt₉Au system, as a result of the decreasing resonance peaks of sp hybridization near the Fermi level. Compared to pure Pt₁₀ cluster, the lower energy barriers and larger reaction energies on Pt₆Au₄ cluster suggest a higher catalytic activity of PtAu cluster for the O₂ dissociation and NO oxidation reactions. Our study provides atomic-scale insights into the nature of the interfacial effect that determines NO oxidation on PtAu cluster catalysts.     

Re-examination of Dronino iron meteorite and its weathering products using Mössbauer spectroscopy with a high velocity resolution

Re-examination of Dronino iron meteorite and products of its weathering in the internal and external surface layers was carried out using Mössbauer spectroscopy with a high velocity resolution. New results showed the presence of α-Fe(Ni, Co), α ₂-Fe(Ni, Co) and γ-Fe(Ni, Co) phases with variations in Ni concentration in Dronino metallic iron alloy. The surface weathering products were supposed as magnetite and/or maghemite, goethite with different particles size and probably ferrihydrite in the internal layer and goethite with different particles size and probably ferrihydrite in the external layer.     

Translation–rotation coupling in the self–diffusion of fluids: molecular dynamic investigation and a generalized exponential approach

Detailed molecular dynamics simulations are carried out to investigate the translation–rotation coupling in linear molecules. We calculated the moment of inertia ratio dependence of the self–diffusion coefficients D, the so–called dynamic isotope effect on the self–diffusion, in pure fluids. Our model systems consist of linear homonuclear pseudo–triatomic rigid molecules for three different molecular sizes over a wide range of density for a given temperature. For a compact representation of our results an exponential approach is employed, which demonstrates a strong translation–rotation coupling on the self–diffusion coefficient in a linear molecule. We find as a main result that in contrast to the low density behaviour at high densities the change of the rotation–translation coupling as a function of the moments of inertia is quite similar for all investigated molecules and we could explain this finding by a careful inspection of the corresponding velocity autocorrelation functions. Finally we present a comparison of experimental data for 20 neat molecular liquids and the corresponding theoretical predictions based on our findings for linear molecules. The good overall agreement indicates that our approach can be generalized and is therefore not only a compact representation of the calculated data but has also large predictive capabilities.     

Mössbauer studies of raw materials from Misti volcano of Arequipa (Peru) for its potential application in the ceramic field

We would like to introduce, the study of two different colour “sillar” samples: white and pink, belonging to the Añashuayco quarry in the Arequipa Region (Peru). The X-ray diffraction (XRD) analysis indicates the presence of several mineralogical phases, such as feldpars and biotite for the both white and pink “sillar” whereas cristobalite and quartz are detected only in the first sample and amorphous phase in the second one. In room temperature, Mössbauer spectroscopy, the presence of hematite (α-Fe₂O₃) was detected as the main phase for both samples, this was not detected in the XRD measurements. Moreover, corresponding doublets in the Mössbauer spectra indicate the presence of iron in the aluminium-silicate minerals. The rates Fe^2?+?/Fe^3?+? are 0.0752 and 0.0526 to the white and pink samples respectively. The minerals composing the white tuff form a heterogeneous aggregate of uniform aspect. Mining of these materials generates a great amount of waste in the form of lumps of varying size and which are raw materials studied in the present work for potential application in the ceramic field.     

Structural and spectroscopic properties of the diazocarbene radical (CNN) and its ions CNN+ and CNN−: a high-level theoretical investigation

The diazocarbene radical, CNN, and the ions CNN⁺ and CNN^? were investigated at a high level of theory. Very accurate structural parameters for the states X ³Σ^? and A ³Π of CNN, and X ²Π of both CNN⁺ and CNN^? were obtained with the UCCSD(T) method using correlated-consistent basis functions with extrapolations to the complete basis set limit, with valence only and also with all electrons correlated. Harmonic and anharmonic frequencies were obtained for all species and the Renner parameter and average frequencies evaluated for the Π states. At the UCCSD(T)/CBS_T-5 level of theory, Δ_f H(0 K) = 138.89 kcal/mol and Δ_f H(298 K) = 139.65 kcal/mol were obtained for diazocarbene; for the ionization potential and the electron affinity of CNN, 10.969 eV (252.95 kcal/mol), and 1.743 eV (40.19 kcal/mol), respectively, are predicted. Geometry optimization was also carried out with the CASSCF/MRCI/CBS_T-5 approach for the states X ³Σ^?, A ³Π, and a ¹Δ of CNN, and with the CASSCF/MRSDCI/aug-cc-pVTZ approach for the states b ¹Σ⁺, c ¹Π, d ¹Σ^?, and B ³Σ^?, and excitation energies (T_e) evaluated. Vertical energies were calculated for 15 electronic states, thus improving on the accuracy of the five transitions already described, and allowing for a reliable overview of a manifold of other states, which is expected to guide future spectroscopic experiments. This study corroborates the experimental assignment for the vertical transition X ³Σ^? ← E ³Π.     

197Au Mössbauer study of the deactivation and reactivation of a carbon-supported AuCl 4 − hydrochlorination catalyst

Acetylene hydrochlorination catalysts consisting of activated carbon impregnated with a solution of HAuCl₄·xH₂O in aqua regia have been studied by¹⁹⁷Au Mössbauer spectroscopy. The relative amounts of AuCl ₄ ^? , of Au(0), and of an Au(J) species formed under certain process conditions were determined quantitatively. Deactivation of the catalyst at low and high temperatures was shown to be due to different mechanisms, and the reactivation of the catalyst by Cl₂ gas was studied.     

Mössbauer characterisation of Fe–polygalacturonate as a medicine for human anaemia: the effect of iron concentration

⁵⁷Fe Mössbauer spectroscopy was used to study the effect of iron concentration on the oxidation state and microenvironments of iron in Fe–polygalacturonate compounds prepared by a novel method from pectin. The iron concentration of the coordination compounds was determined by inductively coupled plasma optical emission spectrometry analysis. The Mössbauer spectra of the studied compounds could be decomposed into three markedly different quadrupole doublets referring to three microenvironments. Two of these have ferrous and one has ferric oxidation state. In the applied concentration range the relative occurrence of the ferric component was found to increase considerably with iron concentration. At the same time, with increasing iron concentration the relative occurrence characteristic of the three components showed saturation behaviour up to the iron concentration at which for each pair of galacturonic acid units there is on average one iron atom in the system, which iron concentration value is interpreted as to be related to the complete fill up of certain iron complexation sites of the polygalacturonate chains.     

Justification of the discrete nonlinear Schrödinger equation from a parametrically driven damped nonlinear Klein–Gordon equation and numerical comparisons

We consider a damped, parametrically driven discrete nonlinear Klein–Gordon equation, that models coupled pendula and micromechanical arrays, among others. To study the equation, one usually uses a small-amplitude wave ansatz, that reduces the equation into a discrete nonlinear Schrödinger equation with damping and parametric drive. Here, we justify the approximation by looking for the error bound with the method of energy estimates. Furthermore, we prove the local and global existence of solutions to the discrete nonlinear Schrödinger equation. To illustrate the main results, we consider numerical simulations showing the dynamics of errors made by the discrete nonlinear equation. We consider two types of initial conditions, with one of them being a discrete soliton of the nonlinear Schrödinger equation, that is expectedly approximate discrete breathers of the nonlinear Klein–Gordon equation.