The 57Fe Mössbauer spectrum obtained after 57Mn (T1/2 = 1.45 min) implantation of solid hydrogen was measured at 7 K. The spectrum was analyzed as three components, and the chemical species of each component was assigned from the obtained Mössbauer parameters and the results of density functional theory (DFT) calculations. The formation process of chemical species and the oxidation states of Fe atoms produced by β– decay of 57Mn are discussed considering the charge transfer process, in relation to previous emission Mössbauer spectroscopy experiments with 57Co implantation of solid hydrogen at low temperature.

In-beam Mössbauer spectra of 57Mn implanted into LiAlH4 were measured at different temperatures between 17 and 300 K. The Mössbauer spectrum measured at 17 K showed two sets of doublets, which were assigned to 57Fe atoms at substitutional sites at Al3+ and Li+ sites. The Debye temperatures θM for the 57Fe atoms at Al3+-substituted and Li+-substituted sites were estimated to be 194 K and 117 K, respectively. The assignments were confirmed by density functional theory calculations.

Although O3-NaFe1/2 Mn1/2 O2 delivers a large capacity of over 150 mAh g-1 in an aprotic Na cell, its moist-air stability and cycle stability are unsatisfactory for practical use. Slightly Na-deficient O3-Na5/6 Fe1/2 Mn1/2 O2 (O3-Na5/6 FeMn) and O3-Na5/6 Fe1/3 Mn1/2 Me1/6 O2 (Me = Mg or Cu, O3-FeMnMe) are newly synthesized. The Cu and Mg doping provides higher moist-air stability. O3-Na5/6 FeMn, O3-FeMnCu, and O3-FeMnMg deliver first discharge capacities of 193, 176, and 196 mAh g-1 , respectively. Despite partial replacement of Fe with redox inactive Mg, oxide ions in O3-FeMnMg participate in the redox reaction more apparently than O3-Na5/6 FeMn. X-ray diffraction studies unveil the formation of a P-O intergrowth phase during charging up to >4.0 V.

To investigate the interactions of 57Fe atoms with sulfur hexafluoride SF6 molecules, in-beam Mössbauer spectra were measured for 57Mn implanted SF6 at 9 K and 65 K. Isolated 57Fe atoms or ions produced by β-decay were not trapped within the SF6 matrix. At 9 K, monomeric FeF2 and FeF3 molecules were produced by reaction of 57Fe with F atoms released by decomposition of the SF6 molecules. When the temperature of the SF6 solid was increased to 65 K, FeF4 was formed in addition to FeF2 and FeF3. Density functional calculations were performed to confirm the assignments of the candidate species identified in the Mössbauer spectra.

Infrared spectra of the photochemical products of bis(cyclopentadienyl)dicarbonyl titanium, TiCp2(CO)2, isolated in an Ar matrix and a N2 matrix were measured. UV-irradiation of TiCp2(CO)2 produced TiCp2(CO) in the Ar matrix, and three types of nitrogen-containing compounds, TiCp2(CO)(N2), TiCp2(N2), and TiCp2(N2)2 were produced in the N2 matrix. The yields of the species changed with the duration of UV-irradiation. Annealing of the sample resulted in the disappearance of unstable TiCp2(N2) and an increase of TiCp2(N2)2. Isotope shifts of the infrared spectra were measured using 15N2 to confirm the assignments. The structures of the species were estimated using a double hybrid density functional theory calculation (mPW2PLYP/cc-pVTZ), and the calculated infrared frequencies were in very good agreement with the experimentally measured spectra.

This review describes the synthesis of iron-based nanoparticles. Iron oxyhydroxide, iron oxide, iron carbide, and iron sulfide nanoparticles have been produced using various methods. Feroxyhyte δ-FeOOH nanoparticles were produced by the oxidation of precipitates obtained by hydrazine reduction of iron chloride. Similar nanocomposites doped with foreign atoms (Ag, Cu, or Zn) have been produced as well. Iron oxide (γ-Fe2O3) nanoparticles have been produced by a polyol method. When a sulfide source was added into the solution during synthesis, iron sulfide nanoparticles were obtained. Using this technique, a metastable trivalent iron sulfide (Fe2S3) was successfully synthesized. Amorphous iron/carbon particles were obtained by the sonochemical synthesis of ferrocene in diphenylmethane. Subsequent heating of the amorphous particles produced Fe3C, α-Fe, and γ-Fe nanoparticles. Laser ablation of iron metal in an organic solvent produced iron carbide nanoparticles. The reaction mechanism and the structures of the nanoparticles were studied using Mössbauer spectroscopy as well as X-ray diffraction and transmission electron microscopy.

Iron nitrides with a high nitrogen content are metastable and can be prepared in the form of fine particles or as a film. An arc discharge of iron metal in a reactive atmosphere provides a convenient method to produce iron-based films. In this study, iron nitride films were formed on an aluminum substrate by arc deposition of iron in a nitrogen atmosphere under a controlled nitrogen flow rate (10–30 sccm). The samples were analyzed by transmission Mössbauer spectroscopy and X-ray diffraction. When the temperature of the aluminum substrate during deposition was maintained at 298 K, ε-Fe3-2N was obtained for nitrogen flow rates in the range 20 to 30 sccm. When the aluminum substrate was heated to 573 K during deposition with nitrogen flow rates of 15 to 30 sccm, a highly crystalline ε-Fe2N film was formed.

Laser ablation in liquid (LAL) is a very useful, conventional means of producing metal particles. While the wet chemical synthesis of nanoparticles typically requires numerous chemical reagents and complicated handling processes, LAL provides a very simple method of generating nanoparticles while reducing the amount of reagents. Furthermore, so-called naked nanoparticles without coating materials can be obtained using LAL, which provides a facile approach to studying the properties of such materials. Laser-based synthesis and processing have been studied extensively, as has the LAL process itself. Both fragmentation and melting resulted from laser irradiation (LI) of particles suspended in liquid have been found to be important. Laser ablation (LA) of a metal has been shown to produce a plasma vapor that is rapidly quenched by the surrounding solvent to produce particles. In the case that the surrounding solvent is itself decomposed by the plasma vapor, the subsequent reactions can produce particles of various metal compounds. The chemical composition and structure of these nanoparticles can be controlled by tuning the LA conditions and varying the solvent. In addition, in the case that LA is performed in a stagnant solvent, the resulting particles can be said to undergo LI. LI increases the temperature of particles, and the fragmentation and melting of the particles change their chemical composition or their shapes. Using this LAL technique, it is possible to produce metastable materials, and our own group has demonstrated the generation of metastable copper oxide particles (Cu4O3) by LA in water. We have also reported the reaction of iron in organic solvents to produce iron carbide particles. The LA of iron in alcohols gave α-Fe, γ-Fe, Fe3C and amorphous iron carbides. Using this technique in conjunction with a solvent f low allowed separation and collection of the different nanoparticles immediately after production, preventing further photochemical reactions of the material. The effect of LI on iron carbide nanoparticles produced by LA has also been studied, and has been shown to increase the particle size and to change the composition to pure Fe3C. The LA of iron in various liquids has been examined. The formation of α-Fe particles via LA of iron in water has been investigated, with the surfaces of the α-Fe particles protected by surface-stabilizing reagents. The fabrication of FeO nanoparticles based on LA of a pure iron plate in poly (vinylpyrrolidone) solutions has also been reported, during which the particle size was controlled by varying the surfactant concentration. Generally, LA of metallic iron in water without an adequate supply of surfactant produces iron oxide particles. It has been proposed that the LA process generates Fe clusters that react with adjacent H2O molecules to form Fe(OH)2 nanopar ticles, which subsequently decompose to FeO nanoparticles at high temperature and pressure. In other work, iron oxide nanoparticles consisting of a mixture of hematite and magnetite were obtained by LA of metallic iron in water. The size of such iron oxide nanoparticles can evidently be controlled by applying LI, although Mössbauer spectra of the particles were not obtained in previous studies. In the present study, LA of metallic iron in flowing water was performed to produce LA particles that were then further modified by LI in water. These LA and LI processes were analyzed separately to better understand the LAL mechanism.

Metastable iron carbide thin films (χ-Fe5C2 and o-Fe7C3) were produced by pulsed laser deposition of Fe in a CH4 atmosphere, and their Mössbauer spectra and X-ray diffraction patterns were measured. Films consisting of amorphous Fe-C carbide were obtained when the substrate temperature was kept at 300 K during deposition, while crystalline films were produced for a substrate temperature of 573 K. The effect of CH4 pressure was investigated. Films produced below 4.0 Pa consisted of a combination of χ-Fe5C2 and α-Fe, and single-phase carbide films were produced at higher pressure: pure χ-Fe5C2 and o-Fe7C3 films were produced at 4.0 and 6.0 Pa, respectively. At 13 Pa, a film was produced consisting of o-Fe7C3 and paramagnetic amorphous Fe-C containing a large amount of C atoms. The film produced at the highest pressure of 40 Pa consisted solely of paramagnetic amorphous Fe-C.

Cu-doped maghemite (γ-Fe2O3) and Cu-doped feroxyhyte (δ-FeOOH) nanoparticles were synthesized using a wet chemical method. The synthesis was performed starting from a mixture of iron and copper salts. Cu-doped γ-Fe2O3 and Cu metal nanoparticles were obtained from a solution with a high Cu/Fe ratio, whereas Cu-doped δ-FeOOH nanoparticles were obtained from a solution with a low Cu/Fe ratio. The size of the nanoparticles was below 10 nm. The superparamagnetic behavior of the nanoparticles was determined from their Mössbauer spectra. The hyperfine magnetic field of Cu-doped δ-FeOOH nanoparticles was larger than that of undoped δ-FeOOH nanoparticles. The Cu content of the intermediate species plays an important role in the oxidation process. The intermediate species in the precipitates before rinsing was speculated to be Cu1-xFeIIxFeIII2O4 (x = 0.4–0.7), which was subsequently oxidized in air to form Cu-doped γ-Fe2O3 or Cu-doped δ-FeOOH, depending on the amount of Cu.

Mn-doped feroxyhyte (δ-FeOOH) nanoparticles were synthesized using a wet chemical method, starting from a mixture of iron and manganese salts. The particles obtained were needle-like, around 100 nm in length, and formed had a nano-urchin structure. The compositions of the four samples obtained were calculated to be δ-Fe0.92Mn0.08OOH, δ-Fe0.75Mn0.25OOH, δ-Fe0.56Mn0.44OOH, and δ-Fe0.32Mn0.68OOH. The superparamagnetic behavior of the nanoparticles was determined from their room-temperature Mössbauer spectra. The hyperfine magnetic field of the Mn-doped δ-FeOOH nanoparticles decreased when iron atoms were substituted by Mn atoms. Furthermore, Mn atoms were locally doped into δ-FeOOH.

Synchrotron-Radiation-based \(^{\mathrm {149}}\)Sm Mössbauer spectroscopy was applied to Sm intermetallics, SmBe13 and SmTi2Al20. Temperature dependence of the Mössbauer parameters in SmBe13 indicate the Sm valence state is purely trivalent. SmBe13 also showed second-order Doppler shift in synchrotron-radiation-based \(^{\mathrm {149}}\)Sm Mössbauer spectroscopy. The Mössbauer parameters obtained in SmTi2Al20 suggest that the Sm valence is fluctuating and the magnitude of the magnetic moment is reduced by hybridization between 4f and conduction electrons and/or effect of crystal electric field.

Zinc-iron oxide nanoparticles (ZnxFe3−xO4 and δ-ZnxFe1−xOOH) were successfully synthesized by room temperature chemical reaction of a solution containing ZnCl2 and FeCl2 in the presence of gelatin. The composition of products could be controlled by variation of the Zn/Fe mixture ratio of the starting material. ZnxFe3−xO4 nanoparticles were obtained from a solution with a high Zn/Fe ratio, whereas Zn-doped feroxyhyte (δ-ZnxFe1−xOOH) nanoparticles were obtained from a solution with a low Zn/Fe ratio. The ZnxFe3−xO4 nanoparticles were spherical with diameters of approximately 10 nm, and the δ-ZnxFe1−xOOH particles were needle-like with lengths of approximately 100 nm. Mössbauer spectra measured at room temperature indicated superparamagnetic behavior of the nanoparticles, whereas the magnetic components were observed at low temperature. The Zn content of the intermediate species (\((\text {Zn}^{\text {II}}_{\mathrm {x}}\text {Fe}^{\text {II}}_{\mathrm {1-x}}\text {Fe}^{\text {III}}_{\mathrm {2}}\mathrm {O}_{4})\)) plays an important role in the oxidation process. When the Zn concentration was high, the content of Fe2+ in the intermediate species was small, and Zn2+ prevented further oxidation of the nanoparticles. When the starting material had low Zn concentration, the amount of Fe2+ in the intermediate species became large and was rapidly oxidized into δ-ZnxFe1−xOOH while rinsing under the ambient atmosphere.

A mixture of acetylacetone and water was condensed in low-temperature Ar matrices at 5 K, and infrared spectra were observed. It was found that the H2O molecules formed hydrogen bonds with the acetylacetone. The structure of the H2O-C5H8O2 complex was estimated with the aid of a density functional calculation. A similar sample was prepared using deuterium-substituted water to confirm the structure of the complex. Upon annealing the matrix-isolated sample, aggregation of H2O molecules was observed and the amount of the complex remained unchanged. (C) 2017 Elsevier Inc. All rights reserved.

A mixture of silver and iron oxide nanoparticles were synthesized by the reaction of FeSO4, AgNO3, and N2H4 in the presence of gelatin at room temperature. The silver/iron oxide nanoparticles were subsequently examined using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Mössbauer spectroscopy. TEM observations revealed two distinct sizes of nanoparticles. The small nanoparticles with diameters of less than 10 nm were assigned to maghemite, and the large particles with diameters of approximately 20 nm were assigned to metallic silver. A Mössbauer spectrum of the maghemite nanoparticles at room temperature showed superparamagnetic behavior due to the small particle sizes. The Mössbauer spectrum measured at low temperature showed a magnetic sextet and a component of distributed hyperfine magnetic fields (DHMF). The DHMF component corresponded to the surface or defects of the maghemite nanoparticles. Silver enhanced the production of maghemite nanoparticles, and the size of the maghemite particles could be controlled by varying the amount of silver salt.

Copper ferrite nanoparticles were synthesized via the oxidation of precipitates obtained from the reaction of FeCl 2 , CuSO 4 and N 2 H 4 in the presence of gelatin. These copper ferrite particles were subsequently examined using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Mössbauer spectroscopy. The average size of the copper ferrite nanoparticles was less than 5 nm, and they exhibited superparamagnetic behavior as a result of their small size. The low temperature Mössbauer spectrum exhibited three sets of sextets, two corresponding to the tetrahedral and octahedral sites of the copper spinel structure and one with small hyperfine magnetic field corresponding to the surface or defects of the nanoparticles. When the ratio of copper salt was increased, the tetrahedral site became preferable for copper, and metallic copper and copper ferrite were both present in a single nanoparticle.