Lancaster delftware: a Raman spectroscopy,electron microscopy and Mössbauer spectroscopy compositional study

In 2008, excavations were conducted by the Northern Ceramic Society at the site of the former Lancaster delftware potworks, which operated between 1754 and about 1790. The recovered sherds have been non‐destructively examined by Raman and electron microscopies and the iron phases in the biscuit by Mössbauer spectroscopy. These methods have provided a new understanding of the mineralogy of the delftware produced at Lancaster using clay imported from Carrickfergus in Ireland and blended with the local ferruginous‐aluminous clays. This has implications for the attribution of delftware produced at Liverpool, Bristol, Scotland and Ireland. The Carrickfergus clay has been found to be highly dolomitic resulting in the body of the delftware forming diopside and the magnesian olivine forsterite, when fired. Brookite had not converted to rutile, nor had tridymite, nor cristobalite formed; the K‐feldspars did not undergo further chemical reactions, and the observation of metakaolin would suggest that the biscuit firing temperature was in the order of 800–900 °C. Chalcedony containing moganite was established as the silica source. A cobalt‐containing lead‐tin glaze was applied to the biscuit body and, after decorating, was fired. The mineralogy of the pigments used to decorate the objects indicate the yellow to be the PbSbSn triple oxide, the green to be a copper silicate mixed with lead‐tin yellow, the purple and browns to be manganese silicates and the blue to contain cobalt spinels and cobalt pyroxenes. Diopside crystals together with recrystallised tin agglomerates have been observed floating within the glaze. Copyright © 2015 John Wiley & Sons, Ltd.     

Raman spectroscopy of Limehouse porcelain sherds supported by Mössbauer spectroscopy and scanning electron microscopy

The Limehouse pot works, founded probably in the early 1745, was one of the earliest porcelain works established in England. It closed in June 1748. The factory site at 20 Fore Street Limehouse, London, was excavated by the Museum of London, Department of Greater London Archaeology in 1990, recovering 1402 sherds. A number of these sherds has now been examined by Raman spectroscopy, scanning electron microscopy and one by Mössbauer spectroscopy. Different porcellaneous formulations have been identified; namely, an experimental Si–Al body with a Si–Al–Ca glaze and a Si–Al–Ca body containing minor Pb and Mg and covered with a Si–Pb–Ca glaze. Several sherds were intermediate between these compositions. Most sherds failed to reach vitrification temperature and lack translucency. Mössbauer spectroscopy indicated that one sherd had been fired under mildly reducing conditions. These results have enabled conclusions to be reached in respect of the raw materials, body and glaze compositions and firing and glazing conditions used at Limehouse. Copyright © 2013 John Wiley & Sons, Ltd.     

Mössbauer spectroscopy of Fe-Ni and Fe-Pt alloys

Mössbauer measurement on Fe-Ni and on Fe-Pt in the ordered and disordered states at various temperatures and in a longitudinal external field (H_ext = 50 kOe) have been analyzed. Hyperfine field distributions of Fe-Ni Invar alloys indicate that in addition to the ferromagnetic phase a second phase or state exists whose magnetic properties seem to be closely related to those of γ-Fe. No second phase or state was detected in the ordered Fe-Pt, while the situation in disordered Fe-Pt is uncertain.     

Characterization of a mechanochemically activated titanium-hematite mixture: Mössbauer spectroscopy study

Mechanochemical processes involving reactions between metals and crystalline oxides are of interest because of their potential technological applications in structural, magnetic or electric materials. In addition they can contribute to the understanding of the natural occurring processes that lead to the formation of minerals and soils. The controlled studies of how the distribution of cations in the titanomagnetites takes place can help toward building a model for the nature of their magnetism and, since they are the primary carriers of rock and soil magnetism, are therefore intensively investigated in many experimental and theoretical studies.In behalf of a better comprehension of the thermal, physical–chemical, magnetic and hyperfine behavior, we have considered a titanium and hematite mixture, with molar ratio Ti:Fe₂O₃ of 1:2, mechanochemically activated during different activation times. We have studied the development of new phases by X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy. The evolution from the starting materials affected by different milling times and subsequent annealing shows that Ti reduces the Fe ions in the Fe₂O₃ lattice, partly to Fe²⁺ and partly to metallic Fe.     

Mössbauer study of chromium-substituted nickel ferrites

The structural and magnetic properties of the Cr substituted NiCr_xFe_1−xO₄ (0x1.4) spinel ferrites have been investigated by means of X-ray diffraction and Mössbauer spectroscopy techniques. Their crystal structures are found to be pure cubic phases. The Mössbauer spectra at 295 and 78 K of all samples showed two well-resolved magnetic patterns corresponding to the tetrahedral A-sites and octahedral B-sites. The cation distributions driven from the area under resonance curve of each site revealed that the compounds are gradually transferred from perfect inverse spinel to partially normal spinel structure. The behavior of the magnetic properties as a function of Cr³⁺ concentration has been explained on the basis of the driven cation distribution and it showed that the chrome-rich compositions can be explained in terms of the non-collinear spin model.     

Conversion electron Mössbauer study of amorphous FeSi thin films

Amorphous FeSi films deposited at 77 K and at room temperature were studied by CEMS. The CEMS reflection spectra for bulk FeSi show quadrupole splittings, ΔE_S, larger by ～ 0.04 mm sec^?1 than ΔE_B - the ones shown by transmission spectra.For amorphous FeSi films ΔE was found (a) to decrease with the thickness of the film, and (b) to be by 25% larger for an amorphous film than for a crystallized one (of the same thickness).The crystallization was found to start at 240°C for a 300 Å thick film.     

Grazing‐incidence synchrotron‐radiation 57Fe‐Mössbauer spectroscopy using a nuclear Bragg monochromator and its application to the study of magnetic thin films

Energy‐domain grazing‐incidence ⁵⁷Fe‐Mössbauer spectroscopy (E‐GIMS) with synchrotron radiation (SR) has been developed to study surface and interface structures of thin films. Highly brilliant ⁵⁷Fe‐Mössbauer radiation, filtered from SR by a ⁵⁷FeBO₃ single‐crystal nuclear Bragg monochromator, allows conventional Mössbauer spectroscopy to be performed for dilute ⁵⁷Fe in a mirror‐like film in any bunch‐mode operation of SR. A theoretical and experimental study of the specular reflections from isotope‐enriched (⁵⁷Fe: 95%) and natural‐abundance (⁵⁷Fe: ～2%) iron thin films has been carried out to clarify the basic features of the coherent interference between electronic and nuclear resonant scattering of ⁵⁷Fe‐Mössbauer radiation in thin films. Moreover, a new surface‐ and interface‐sensitive method has been developed by the combination of SR‐based E‐GIMS and the ⁵⁷Fe‐probe layer technique, which enables us to probe interfacial complex magnetic structures in thin films with atomic‐scale depth resolution.     

Mössbauer charge density in I

The electronic charge density at ¹²⁹I^- is calculated from the Hartree-Fock wave functions in the lithium iodide lattice and from that it is found that the charge density varies approximately as the inverse seventh power of the interatomic distance.     

Mössbauer spectroscopy evidence of intrinsic non‐stoichiometry in iron telluride single crystals

The FeTe parent compound for iron‐superconductor chalcogenides was studied applying Mössbauer spectroscopy accompanied by ab initio calculations of electric field gradients at the iron nuclei. Room‐temperature (RT) Mössbauer spectra of single crystals have shown asymmetric doublet structure commonly ascribed to contributions of over‐stoichiometric iron or impurity phases. Low‐temperature Mössbauer spectra of the magnetically ordered compound could be well described by four hyperfine‐split sextets, although no other foreign phases different from Fe_1.05Te were detected by XRD and microanalysis within the sensitivity limits of the equipment. Density functional ab initio calculations have shown that over‐stoichiometric iron atoms significantly affect electron charge and spin density up to the second coordination sphere of the iron sub‐lattice, and, as a result, four non‐equivalent groups of iron atoms are formed by their local environment. The resulting four‐group model consistently describes the angular dependence of the single crystals Mössbauer spectra as well as intensity asymmetry of the doublet absorption lines in powdered samples at RT. We suppose that our approach could be extended to the entire class of FeSeTe_x compounds, which contain excess iron atoms.

     

A Fe Mössbauer study of Mn2P

It is shown that ⁵⁷Fe substitutes for Mn(1) in Mn₂P. The Néel temperature is found to be 110 K and the magnetic moments for the iron atoms are estimated to be 0.63μ_B. All iron atoms have the same moment in contrast to what was found for Mn(1) atoms in an earlier neutron diffraction study by Yessik. A magnetic triangular substructure for Mn(1) is therefore proposed.     

In-situ conversion electron Mössbauer spectroscopy on Fe(110)-surfaces and thin films

Using in-situ conversion electron Mössbauer spectroscopy the layer-by-layer analysis of epitaxial 21-monolayer Fe(110)-films on W(110) was carried out. The hyperfine interaction parameters near the Ag-coated and free Fe(110) surfaces could be measured with the monolayer resolution. The quadrupole interaction deviates strongly from zero in the topmost iron monolayer. The reduction of hf-magnetic field for the free surface is demonstrated. The temperature dependence of the hf-magnetic field across the Ag-coated films is discussed.This work was supported by the Stiftung Volkswagenwerk.     

Studying surfaces and thin films using Mössbauer spectroscopy

Using a series of bi-layer samples, we show how Conversion Electron Mössbauer Spectroscopy (CEMS) and X-ray Backscatter Mössbauer Spectroscopy (XBS) can be done with the same experimental set up. The penetration depths of the K and L conversion electrons are measured as 51(6) and 330(240) nm, respectively, with relative contributions of 88(9) and 12(9)%. The penetration depth of the Fe-K _α X-ray signal is determined to be 3.6(2) μm. As a demonstration we show data on surface damage effects in electropolished TRIP steels, and by comparing CEMS and XBS Mössbauer patterns we estimate the thickness of a damaged layer (created by sanding) to be 550(50) nm.     

Surface and interface properties of epitaxial Fe3O4 films studied by Mössbauer spectroscopy

Stoichiometric Fe₃O₄ films have formed epitaxially on -Al₂O₃ and MgO single-crystal substrates by a reactive vapor deposition method. In order to apply conversion electron Mössbauer spectroscopy depth-selectively, a 5–7 Åthick probe layer containing ⁵⁷Fe was formed at various depths in inactive ⁵⁶Fe₃O₄ matrix films. At the topmost surfaces and also at the interfaces, the essential electronic features of bulk Fe₃O₄ are retained, including a rapid electron hopping between the Fe²⁺ and Fe³⁺ ions at B sites. Minor depth-dependent changes are confined to a few outermost atomic layers, and the changes depend on the orientation and the lattice mismatch with the substrate. For (111) growth on -Al₂O₃, the surface layer seems to be strongly relaxed to reduced the electric polarization, while a high density of defects seems to be concentrated at the interface with -Al₂O₃. For (001) growth on MgO, the surface retains the spinel lattice though slightly oxidized, while the interface with MgO has good crystallinity and stoichiometry. An enhanced thermal fluctuation of the Fe³⁺-spins in contact with the MgO substrate and in the topmost surface layer can be seen in their reduced magnetic hyperfine field at 300 K.     

Observation of hydrogen induced intermediate borides in PrFeB based alloys by Mössbauer effect spectroscopy

In the present work, a quantitative analysis of the phase compositions by Mössbauer effect spectroscopy of solid and conventional hydrogen disproportionated Pr_13.7Fe_80.3B_6.0 and Pr_13.7Fe_63.5Co_16.7Zr_0.1B_6.0 alloys was carried out. Significant amounts of intermediate borides t-Fe₃B and Pr(Fe, Co)₁₂B₆ were detected after solid hydrogen disproportionation treatment in Pr_13.7Fe_80.3B_6.0 and Pr_13.7Fe_63.5Co_16.7Zr_0.1B_6.0 alloys, respectively. After conventional hydrogenation–disproportionation–desorption–recombination treatment these phases were not detected and in no case residual Pr₂Fe₁₄B-phase was found. It was observed that the amount of intermediate borides after disproportionation can be correlated with the degree of texture after recombination at various temperatures.     

Identification of the intercalant species in SbCl5-graphite using Mössbauer spectroscopy

¹²¹Sb Mössbauer spectra of SbCl₅-graphite have been obtained. The spectra provide clear evidence for the presence of the acceptor molecular ion SbCl₆^-(Sb⁵⁺ and neutral SbCl₃(Sb³⁺ in the intercalate layers, with weak evidence for neutral intercalated SbCl₅. Lineshape analyses of the Sb³⁺ region of the spectra further indicate that two chemical Sb³⁺ sites fit the data significantly better than one site. We attribute the second Sb³⁺ site to SbCl₄^- and find the concentration ratio [SbCl₄^-]/[SbCl₃] 0.25. Samples prepared by the reaction of graphite with vapor mixtures of SbCl₅ and SbCl₃ were found to exhibit dramatically higher concentrations of SbCl₃ than those samples prepared from a reaction with SbCl₅ alone. This latter result is interesting in view of the fact that the reaction of graphite with SbCl₃ vapor does not lead to an intercalation compound.     

Mössbauer of γFe-Ni alloys

Mössbauer measurement performed as a function of temperature show quite different patterns for iron and nickel rich γ Fe-Ni alloys. Isotropic magnetic and additionally both anisotropic magnetic and electric contributions from neighbour atoms to the hyperfine interactions are considered. The temperature dependence of the isotopic contributions suggests the exchange integral J_FeFe to be not constant.     

Extraterrestrial magnetite studied by Mössbauer spectroscopy

The meteorite Orgueil is a carbonaceous chondrite of type CI. Carbonaceous chondrites contain Fe(III), Fe(II) and in some cases metallic iron, indicating that they are in a state far from thermodynamic equilibrium. In Orgueil about 40% of the iron is present in magnetite (Fe₃O₄). In this work a sample of magnetite grains extracted from Orgueil has been studied by Mössbauer spectroscopy. It has been found that the magnetic phase contains about 11% of maghemite and that the remaining magnetite has a vacancy concentration smaller than 0.006, corresponding to the formula Fe_2.994O₄.     

Some Mössbauer effect considerations in gamma-ray laser development

The development of gamma-ray lasers (grasers) will, in all probability, depend on the use of recoillessly emitted gamma rays from nuclear transitions, i.e., the Mössbauer Effect (ME). Past research in Mössbauer spectroscopy which relates to grasers is briefly reviewed. The nuclear lifetimes, required for practical considerations, may have to be on the order of seconds, if storage and transfer processes prove infeasible. It is not clear that the ME has been observed in such long-lived states. Even if such long-lived states are not needed directly for grasers, successful observation of the ME in such a system will answer important questions of line broadening due to field inhomogeneities in single crystals. We propose some novel experimental schemes to observe the ME in ¹⁰⁹Ag whose relevant lifetime is about 40 sec. The techniques proposed are: coincidence Mössbauer spectroscopy, conversion-electron Mössbauer spectroscopy, gravitational line sweeping, and gamma-ray self-absorption. Preliminary results using the later technique are presented. Possible future, relevant ME research is discussed.     

Conversion electron Mössbauer spectroscopy of r.f. sputtered Cd0.95 Fe0.05 Te thin films

CEMS studies have been performed on Cd_0.95 Fe_0.05 Te films grown by r.f. supttering on quartz and silicon substrates. The dependence of the relative amount of Fe²⁺ and Fe³⁺ on substrate type, substrate temperature and annealing temperature is discussed.     

Sputtered metal-silicon thin films studied by auger electron spectroscopy

The silicon KLL Auger spectrum from a range of stainless steel-silicon thin films was studied to provide information on changes in the silicon-silicon to silicon-metal bond ratio. This work complements earlier Auger spectroscopic studies of stainless steel-carbon films. Unlike the carbon KLL spectrum, the silicon KLL spectrum contains little chemical information. Changes in the principal plasmon loss peak associated with the silicon KLL spectrum may however prove useful in identifying the silicon phases.