Mössbauer study of structural relaxation at the glass transition

Mössbauer spectra of very dilute solutions of ⁵⁷Fe²⁺ ions in propane-(1,2)diol show distinct anomalies in the quadrupole splitting, the linewidth and the recoilfree fraction near the glass transition temperature. The observed time and temperature dependence of these anomalies can be correlated with structural relaxation processes which occur in a glass upon stabilization into the supercooled liquid phase.     

Mössbauer characterization of an amorphous steel with optimal Mo content

Three amorphous steel alloys, Fe_71.2?xC_7.0Si_3.3B_5.5P_8.7Cr_2.3Al_2.0Mo_x (x = 0, 4.5 and 6.5 at.%), have been produced by the melt-spinning technique and characterized by X-ray diffraction and transmission Mössbauer spectrometry (TMS). TMS allows us to study the local environments of the Fe atoms in the glassy state, showing the changes in the amorphous structure due to the addition of Mo. A reduction of the mean hyperfine field is observed as the amount of Mo increases. With intermediate Mo content, this reduction is associated to the substitution of Fe by Mo in a disordered magnetic Fe-rich structure, whereas for high Mo content, this structure is destroyed leading to an increase of paramagnetic environments. Finally, the relationship between the glass forming ability (GFA) of these alloys and their local structure determined by TMS will be discussed.     

Study of alkali borate glass containing tin by the Mössbauer effect

A number of alkali borate glasses containing tin oxide of base composition (100?X) % B₂O₃ + X % Me₂O + Y SnO₂ where Me = Li, Na or K, X = 10, 20 or 30 and Y is the quantity of SnO₂ introduced, were prepared and studied by the Mössbauer effect. It was shown that the value of the isomer shift increases while the value of the quadrupole splitting decreases with increasing ionic radius of the alkali ion. The value of the isomer shift and quadrupole splitting decrease with increasing alkali content. The observed asymmetry in the absorption lines was attributed to the Goldanskii effect. An explanation is suggested for the dependence of the ratio of the various valence and coordination structural states of the tin in the glass on the amount and nature of the alkali ions.     

Synthesis, X-ray and neutron diffraction and Mössbauer studies of SrFeOx crystals

Tetragonal single crystals of the nonstoichiometric strontium ferrate with the lattice parameters a = 3.8525(3) and c = 3.8781 (3) Å have been synthesized for the first time by the method of floating-zone melting in the SrFeO_x system. The neutron diffraction patterns of the crystals showed weak additional reflections indicating the formation of the superstructure with double spacing along the [hh0] direction. The Mössbauer spectra of the crystals were obtained and measured in the temperature range 80–300 K. It was established that below the temperature T _N = 232(1) K, the crystals are in the magnetically ordered state with 3/5 of iron ions being in the trivalent state and all the remaining iron ions in the tetravalent state. This leads to the crystal composition SrFeO_2.71. The electric resistivity of the crystals equal to 100 ω cm at room temperature drastically decreases at temperatures exceeding 470 K.     

Crystal structures of (η5-C5H4COMe)M(CO)3Me (M=Mo,W)

The crystal structures of ( ⁵-C₅H₄COMe)M(CO)₃Me (M=Mo,W) have been determined. They are not isostructural. M=Mo isP2₁/c,a=10.205(6),b=14.192(8),c=8.135(6) Å,=93.43(4)° andD(calc)=1.71 g cm^–3 forZ=4. M=WisP2₁/c,a=12.580(7),b=6.830(5),c=13.750(7) Å,=93.72(4)° andD(calc)=2.20 g cm^–3 forZ=4. Both have a four-legged piano stool geometry with the substituted carbon making the closest M-C( ⁵) approach. The methyl group in the M=W derivative is disordered between twotrans-ligand positions. The average bonding parameters for the more accurately determined Mo analog are: Mo-C()⁵)=2.34(3) Å, Mo-CO=1.98(2) Å, Mo-Me=2.304(4) Å.     

Growth and characterization of Fe1 ? x M x VO4 single crystals (M = Al, Cr, Co, Ga)

Triclinic Fe_{1 ? x} M _x VO₄ single crystals (M = Al, Ga, Co, Cr) have been grown by the flux method from systems based on PbO-V₂O₅. Their crystallographic parameters are determined by powder X-ray diffraction. Fe_{1 ? x} Ga _x VO₄ single crystals (x = 0?C0.3) with a volume more than 1cm³ are grown using the seeding technique. The temperature and field dependences of magnetization and magnetic susceptibility of the grown Fe_{1 ? x} Ga _x VO₄ and Fe_{1 ? x} Al _x VO₄ single crystals (x = 0.3 in the solution-melt) are reported. It is shown that the magnetizations of these crystals exceed that of FeVO₄, and both of their antiferromagnetic phase transitions are shifted to lower temperatures.     

Magnetic Susceptibility of Deintercalated Tunnel Compound of KxCr5Se8 and Mössbauer Spectra of Kx(Cr0.95 57Fe0.05)5Se8

Abstract

KCr₅Se₈ has a TIV₅S₈-type structure, containing K ions in one-dimensional tunnels. Deintercalated samples of K_xCr₅Se₈ (0.32 ≤ x ≤ 0.93) were prepared by leaching method using Alc₃/FeCl₃ aqueous solution. These samples showed a broad peak of magnetic susceptibility at ca. 130 K. ⁵⁷Fe-Mössbauer spectra of K_x(Cr_0.95 ⁵⁷Fe_0.05)₅Se₈ (x = 1.0, 0.49) showed a quadrupole doublet at 300 K. Magnetic sextets appeared at 4.2 K in both samples, indicative of magnetic ordering. The observed isomer shift indicated that the charge of Fe is +3 in both samples. It was proposed that Se^2- was partially oxidized by the deintercalation.     

Study of hyperfine interactions in Fe–Co nanocomposite films by Mössbauer spectroscopy and NMR

Nanogranular magnetic films were produced by the specially designed UHV plasma-jet system with DC hollow-cathode discharge. We investigated the properties of these ferromagnetic FeCo-AlN films. The samples were studied by nuclear magnetic resonance, Mössbauer spectroscopy, and transmission electron microscopy. The films are composed of nanoparticles of cubic FeCo, 2–10 nm in size, embedded in amorphous matrix containing Al, N and O. The Mössbauer spectra indicate that the orientation of local magnetic moments on the surface is random for the sample with 1:1 Fe/Co ratio, while the magnetization lays in the plane of the layer for samples with Fe/Co smaller than 1 (0.91–0.95).     

Structural mechanisms of superionic conductivity in M 1−x R x F2+x single crystals

The relationship between the superionic transport in fluorite phases M _{1 ? x} R _x F_{2 + x} (M = Ca, Sr, or Ba; R are rare earth elements) and their defect structure has been analyzed. The superionic conductivity of M _{1 ? x} R _x F_{2 + x} crystals is provided by the high concentration of charge carriers. However, the carrier concentration is several tens of times lower than the concentration of anionic defects, which is explained by the presence of defect regions (DRs), which partially block carriers. The dependence of the superionic conductivity of M _{1 ? x} R _x F_{2 + x} phases on the RF₃(x) content has a percolation nature. Crystals of these phases are divided into two groups with respect to the percolation threshold: x _{p, 1} = 2–3 mol % RF₃ and x _{p, 2} = 7–8 mol % RF₃. The corresponding DR volumes are 3000–4000 ų (x _{p, 1}) and 500–700 ų (x _{p, 2}). The x _{p, 1}, and x _{p, 2} values correlate, respectively, with the octahedral cubic {M _{14 ? p} R _p F_{68 ? 69}} and tetrahedral {M _{4 ? p} R _p F₂₆} clusters, which are DR cores. The DR model and cluster structure are indicative of the heterogeneity of nonstoichiometric M _{1 ? x} R _x F_{2 + x} crystals at the nanoscale level with respect to the chemical composition and the electrical and crystallochemical (coordinations of M and R) characteristics.     

Structural characterization of a series of cyclohexaphosphates: M0.5((C6H5CH2)2NH2)5P6O18·H2O (M = Co, Cu, Cd)

Three new cyclohexaphosphates with general formula M_0.5((C₆H₅CH₂)₂NH₂)₅P₆O₁₈·H₂O (M=Co, Cu, Cd) are reported. They crystallize with monoclinic unit-cells and are isotropic. We have determined their structure from the salt M=Co. This later exhibits the following unit-cell parameters: a = 22.739(5), b = 17.682(3), c = 18.342(3) Å, = 91.22(1)°, Z = 4,P2₁/n, V = 7373 ų, and Dx = 1.373 g cm^–3. The atomic arrangement can be described as layers containing P₆O₁₈ ring anions and CoO₆ octahedra spreading in the (101) planes and intercalated by the dibenzylammonium groups and the water molecules. Synthesis and characterization by X-ray diffraction, IR absorption, and TA are described.     

Precision X-ray diffraction and Mössbauer studies and computer simulation of the structure and properties of malayaite CaSnOSiO<Subscript>4</Subscript>

The structure and some physical properties of malayaite CaSnOSiO₄ have been studied by the precision X-ray diffraction, Mössbauer spectroscopy, and computer simulation of the structure. The unit-cell parameters a = 7.152(2) Å, b = 8.888(2) Å, c = 6.667(2) Å, β = 113.37(2)°, V = 389.0(3) ų, and μr = 0.68 are refined on a synthetic impurity-free sample. The distribution of the deformation electron density is analyzed in the basic fragments of the crystal structure forming an anionic framework. The constructed potentials of pair and three-particle interaction reproduced quite well the elastic, dielectric, and energy characteristics and allowed us to predict their numerical values, which are in good agreement with the limited available experimental data.     

Synthesis,infrared and Mössbauer characterization and X-ray crystal structure of 1,10-phenanthrolinium tetrachloromethoxy phenylantimonate(V)

The compound has been characterized by X-ray crystal structure determination, Mössbauer and i.r. spectroscopy. It crystallizes in the monoclinic space groupP2 ₁ /c (No. 14) witha=24.228(4),b=8.335(2),c=23.975(4) Å,=117.83(3)° andZ=8. Least-squares refinement on 3749 observed reflections gave finalR=0.034 (R _w=0.037). The compound is constituted by [(C₆H₅)SbCl₄OMe]^– anions andphenH⁺cations. The coordination polyhedron about Sb is an octahedron (Sb-Cl 2.416(3), Sb-O 1.962(7) and Sb-C 2.138(9) Å). The whole structure is characterized by two short contacts (O(1)N(2) 2.76(1) O(2)N(4) 2.75(1) Å) involving the methoxy oxygens of the two independent anionic units [(C₆H₅)SbCl₄OMe]^– and two nitrogens of the two independent phenanthrolinium moieties.     

Eightfold-coordinated diethylenetriaminepentaacetates: Crystal structures of K[M(Dtpa)] ⋅3H2O (M = Zr or Hf) and NH4[Sn(Dtpa)] ⋅ H2O

The crystal structures of K[M(Dtpa)] ? 3H₂O (M = Zr or Hf) and NH₄[Sn(Dtpa)] ? H₂O are studied by X-ray diffraction. The coordination number of the metal atom in all the compounds is eight. The NH₄[Sn(Dtpa)] ? H₂O complex is isostructural to the (H₅O₂)[M(Dtpa)] ? H₂O (M = Sn or Hf) compounds studied earlier.     

Crystallochemical model of ion-transport percolation in nonstoichiometric M 1−x RxF2+x phases with the defect CaF2-type structure

A crystallochemical model of ion-transport percolation in M _1?x R_xF_2+x (M = Ca, Sr, Ba; R = RE) solid solutions with the “defect” CaF₂-type structure has been suggested. Within this model, the percolation thresholds in M _1?x R_xF_2+x crystals with tetrahedral R ₄F_26? and octahedral R ₆F_37? clusters are considered, whose existence is highly probable in these disordered fluorite phases. It is established that the calculated percolation thresholds x _c = 2.8 mol % for nnn (next nearest neighbors) [(R ₆F₃₇) _M6F32 ?F_i] and x _c = 4.7 mol % for nn (nearest neighbor) [(R ₄F₂₆) _M6F32 ?F_i] are in satisfactory accord with the experimental percolation thresholds determined from the conductometric data.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...     

Mössbauer study of nanocrystalline Co60Fe30Ni10 and Co50Fe35Ni15 alloys obtained during mechanical synthesis

The mechanical alloying method was used to prepare Co₆₀Fe₃₀Ni₁₀ and Co₅₀Fe₃₅Ni₁₅ alloys from the elemental powders. As X-ray diffraction studies proved the final products of milling were the solid solutions with b.c.c. lattice and the average grain size of about 60 nm. After heating of the alloys up to 993 K, the mixtures of two solid solutions with a b.c.c. and f.c.c. lattices were formed. Annealing of the alloys at 1173 K for 1 h resulted in the formation of solid solutions with an f.c.c. lattice. Mössbauer spectroscopy revealed hyperfine magnetic field distributions which reflected the different surroundings of ⁵⁷Fe isotopes by Co, Fe and Ni atoms, depending on the chemical composition of the alloy. The most probable atomic configurations were determined on the basis of a local environment model. The results of the macroscopic magnetic measurements testified that Co₆₀Fe₃₀Ni₁₀ and Co₅₀Fe₃₅Ni₁₅ alloys exhibited relatively good soft magnetic properties.     

Peculiarities of the microstructure of a nanoscale modification of η-TiO2

Samples with nanoscale η-TiO₂ phase have been obtained by sulfate and modified sulfate methods and are characterized by a complex of techniques: X-ray diffraction, electron diffraction, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy, and X-ray energy-dispersive analysis. The effect of sample formation conditions on the size and shape of crystallites, content of the amorphous component in the samples, and their elemental composition has been established. A significant change (depending on the synthesis conditions) in the parameters of the diffraction reflection with d ～ 17–21 Å (intensity and interplanar spacing d, Å), pronounced for η-TiO₂, is revealed. This change is most likely related to the variation in the content of water molecules in the interlayer space of η-TiO₂ structure and/or the change in crystallite shape.     

Crystal structure of the Λ-[4M] enantiomer of cis-diaqua-bis(1,3-dimethylpteridine-2,4(1H,3H)-dione-N5,O4) copper(II) perchlorate monohydrate

Single-crystal X-ray diffraction studies have been performed on the complex cis-diaqua-bis(1,3-dimethylpteridine-2,4(1H,3H)-dione-O⁴,N⁵) copper(II) perchlorate monohydrate, [Cu(DLM)₂(H₂O)₂](ClO₄)₂ · H₂O. This compound crystallizes in the orthorhombic system, P2₁2₁2₁ space group, Z = 4 with a = 8.749(1) Å, b = 14.213(1) Å, c = 21.200(2) Å, and V = 2636.2(4) ų. The metal ion is surrounded in octahedral geometry by two mutually quasi-perpendicular N5,O4-coordinated lumazine chelators with the O4 atoms trans and the N5 atoms cis. The polyhedron is completed by two cis-coordinated water molecules. The absolute configuration of the complex can be described, following Bailar's nomenclature, as the enantiomer of the stereoisomer 4M. A three-dimensional hydrogen-bond network is defined by water molecules, perchlorate anions, and the O2 of the pteridine A.