Study on the mechanism of tunable ferromagnetic composites with different rare earth ions

After doping RE elements, the corresponding Ms decreases, and the magnetization decreases with the increase of doping concentration. The RE ions were more inclined to replace some Fe2+ ions in the octahedral position from the VSM results.

Study of Niobium Diffusion and Clusterization in hcp Zr-Nb Dilute Alloys

We perform atomistic simulations aimed on study of diffusion of constituents and niobium precipitation in hcp Zr-Nb. We report diffusivities of Zr and Nb in hcp Zr-Nb alloys computed for the models containing up to 5 at.% of niobium. The calculated diffusivity of niobium rises with increase of its content in the alloy. The simulations also show that for a studied concentration range addition of niobium slightly enhances self-diffusion of zirconium in the alloys. The work is also devoted to description of niobium incorporation and clusterization in hcp zirconium. It is confirmed that for a single niobium atom incorporated in hcp zirconium lattice the octahedral position is the most favorable. We estimated the energy describing niobium cluster formation in pure hcp zirconium. According to the simulation results, we can suggest that the minimum niobium cluster size that can be expected in hcp Zr corresponds to about 80 atoms.

Structure of Magnesium Hydroxide Sulfate [2MgSO4.Mg(OH)2] and Solid Solution in Magnesium Hydroxide Sulfate Hydrate and Caminite

Magnesium hydroxide sulfate [2MgSO4.Mg(OH)2; MHS] is tetragonal with a = 7.454 (1), c = 12.885 (2) Å, V = 716.0 Å3, space group P43212, Z = 4 and D x 2.774 g cm−3. The structure (single-crystal X-ray, R = 0.025, wR = 0.023) comprises spiral (43) single chains of corner-shared Mg(2) octahedra cross-linked by SO4 tetrahedra and face-shared Mg(1) octahedra. A linear ternary group of face-shared Mg octahedra [Mg(2)—Mg(1)—Mg(2)] alternates with an unoccupied octahedral position in rows along [\overline 110]. A crystal of MHS was grown hydrothermally (0.15 GPa, 673 K) from gold-bearing Mg—S—O—H fluid. The MHS structure, with Mg(1) octahedra sharing two octahedral faces with Mg(2) octahedra, revises the structure assumed for the complex solid solution magnesium hydroxide sulfate hydrate and the related ocean-floor mineral caminite [2MgSO4.xMg(OH)2.(2 − 2x)H2O; 0.5 < x < 1.0]. The substitution reaction appears to be Mg(1)2+ ⇋ 2H+. The H-substituted MHS structure is distinguished from that of kieserite (MgSO4.H2O), which has straight single chains of corner-shared Mg octahedra.

ESR and IR Evidence for Chromium in Kaolinites

Evidence obtained from ESR and IR studies is presented for the presence of structural Cr in two natural kaolinites (MILO and GEY) formed in an hydrothermal environment in Sonoma County, California. The XRD patterns show a greater structural disorder for GEY than for MILO, but both have the usual hexagonal shapes as shown by TEM observations. On the basis of EDX analysis of different particles, GEY, on average, appears to be richer in Cr (2.1% Cr203) than MILO (0.6% Cr203). The presence of Fe oxide particles containing some Cr, Ni and V is also indicated by EDX analysis. By FT-IR observation, the octahedral Cr 3+ position was easily detected by a well resolved spectral feature at 3586 cm -1. The adsorbed Cr 3+ kaolinite (KMRXCR) presents no band at 3586 cm -1, but two other bands situated at 3527 and 3477 cm -1. The main features of the ESR spectra of these two kaolinites are a set of resonances near geff4; a broad resonance centred near geff2 with some modulations; and a set of resonances near gcffl. The broad resonance centred near geff2 is interpreted as the free iron oxide signal with modulations due to VO 2+. The set of resonances near geff4 is similar to that observed for octahedral Fe 3+, but the position is shifted compared to that of octahedral Fe 3+. This set of resonances near geff4 is, therefore, interpreted as belonging to Cr 3+ in octahedral position. The resonances at geff1 are also interpreted as belonging to Cr 3-. Comparison with the Cr 3+ surface-adsorbed ESR signal of a Cr-saturated kaolinite (which is a broad resonance centred near geff2) strengthens the interpretation of the geff4 resonances belonging to Cr 3+ in the octahedral position. The results obtained by the combination of FT-IR and ESR spectroscopics indicate that Cr 3+ is present in the octahedral position of the MILO and GEY kaolinites.

Untersuchung des MÖSSBAUER-Effekts in Elpasolithen A2INaFeF6.

57Fe-MÖSSBAUER spectra of the cubic elpasolithes A2INaFeF6 (AI = K, Rb, Cs) show strong single line broadening in the temperature range 4.2 K ≤ T ≤ 600 K. This broadening is attributed to a statistical distribution of differently distorted FeF63-octahedra, causing a statistical distribution of electric fieldgradients at the 57Fe-position. With the aid of a model calculation it was tried to estimate the order of the octahedral distortion. For the compound Rb2NaFeF6 normal to the cell axis an anion displacement of Δ q = 0.11 Å from the regular octahedral position was derived from the Mössbauer data. This value agrees with the root mean square displacement ū = 0.13 Å, which results in this direction from the strongly anisotropic fluorine temperature factors found by X-ray structure determination.

The Synthesis and Structural Studies of some Dialkyltin(IV) Salts of Strong Monobasic Acids

A number of dialkyltin(IV)-bisfluorosulfates, -bistrifluoromethanesulfonates, and -bisdifluorophosphates are synthesized by solvolysis of dialkyltin(IV) chlorides in an excess of the corresponding acid according to [Formula: see text] R = CH3, C2H5, n-C3H7, n-C4H9, and n-C8H17; X = SO3F, SO3CF3, and PO2F2. The structural proposals, hexacoordination for tin with the alkyl groups in trans-octahedral position and bidentate bridging anionic groups with coordination through oxygen, are based on 119Sn Mössbauer, infrared and, where obtainable, Raman spectra. The vibrational spectra of the difluorophosphates are discussed in detail. Variations in isomer shift and quadrupole splitting values with different alkyl groups in all three groups of compounds follow the same regular pattern as in the series R2SnF2. The results of point charge calculations are reported.