A structural and 121Sb Mössbauer-spectroscopic study of PrPdSb and NdPdSb

Phase-pure samples of the antimonides PrPdSb and NdPdSb were prepared by arc-melting pieces of the elements and subsequent annealing. The samples were investigated by powder and single crystal X-ray diffraction: NdPtSb type, space group P63mc, a = 458.70(5), c = 780.55(6) pm, wR2 = 0.0272, 244 F2 values, 11 variable parameters for PrPdSb and a = 458.18(4), c = 771.25(6) pm, wR2 = 0.0317, 229 F2 values, 11 variable parameters for NdPdSb. The palladium and antimony atoms form slightly puckered Pd3Sb3 hexagons which are rotated by 60° in every other layer. The rare earth (RE) atoms are coordinated by two Pd3Sb3 hexagons with the RE–Pd shorter than the RE–Sb contacts. The 121Sb Mössbauer spectra at T = 5 K confirm the antimonide character with isomer shifts of −7.55 (PrPdSb) and −7.47 mm · s−1 (NdPdSb). In agreement with the crystal structures, each spectrum could be fitted with one quadrupole split signal.

Behavior of Graphite and Graphene under Mechanochemical Activation with Hematite and Magnetite Nanoparticles

ABSTRACTEquimolar mixtures of graphene and iron oxide nanoparticles were subjected to mechanochemical activation. The phase sequence was investigated using Mӧssbauer spectroscopy as function of ball milling time. For low milling times (2-4 hours) the series with hematite (Fe2O3) nanoparticles was fitted with 2 sextets, corresponding to hematite with carbon introduced in the lattice. At high milling times (8-12 hours) the same series exhibited an additional sextet with hyperfine parameters characteristic to iron carbides and a quadrupole-split doublet, which could be assigned to carbon clusters with small amounts of iron in them. The series with magnetite nanoparticles (Fe3O4) at low milling times was analyzed considering 2 sextets, corresponding to the tetrahedral and octahedral sites of magnetite. At high milling times, the magnetite series also exhibited a broad sextet representing iron carbides and the doublet associated with iron-containing carbon clusters. Supporting information was obtained by determinations of the recoilless fraction. The results were compared with those obtained by ball milling graphite with hematite and magnetite nanoparticles.

Carbon-Substituted Hematite and Magnetite Nanoparticles

ABSTRACTGraphite-doped hematite and magnetite nanoparticles systems (∼50 nm) were prepared by mechanochemical activation for milling times ranging from 2 to 12 hours. Their structural and magnetic properties were studied by 57Fe Mössbauer spectroscopy. The spectra corresponding to the hematite milled samples were analyzed by considering two sextets, corresponding to the incorporation of carbon atoms into the iron oxide structure. For ball milling time of 12 hours a quadrupole split doublet has been added, representing the contribution of ultrafine particles. The Mössbauer spectra of graphite-doped magnetite were resolved considering a sextet and a magnetic hyperfine field distribution, corresponding to the tetrahedral and octahedral sublattices of magnetite, respectively. A quadrupole split doublet was incorporated in the fitting of the 12-hour milled sample. The recoilless fraction for all samples was determined using our previously developed dual absorber method. It was found that the recoilless fraction of the graphite-doped hematite nanoparticles decreases as function of ball milling time. The f factor of graphite-containing magnetite nanoparticles for the tetrahedral sites stays constant, while that of the octahedral sublattice decreases as function of ball milling time. These findings reinforce the idea that carbon atoms exhibit preference for the octahedral sites of magnetite.

Synthesis and Characterization of Indium Oxide Doped Hematite xIn2O3·(1-x)α-Fe2O3 Solid Solution

ABSTRACTIndium oxide-doped hematite xIn2O3·(1-x)α-Fe2O3 (x = 0.1-0.7) solid solution systems were synthesized using mechanochemical activation. The microstructures, magnetic and thermal properties of the system were dependent on In2O3 molar concentration x and ball milling time. XRD results showed that the completion of In3+ substitution of Fe3+ in hematite lattice occurs after 12 h ball milling for x = 0.1. For x = 0.3, 0.5 and 0.7, the substitutions between In3+ and Fe3+ into hematite and In2O3 lattices occur simultaneously. The lattice parameters of hematite and In2O3 vary as a function of ball milling time. The change in these parameters was due to ions substitution between In3+and Fe3+ and the decrease in grain sizes. Mössbauer spectra of the system with x = 0.3 were fitted with three sextets and two quadrupole-split doublets after milling, representing In3+ substitution of Fe3+ in hematite lattice and Fe3+ substitution of In3+ in two different sites of In2O3 lattice. TGA results showed that the hematite decomposition is enhanced due to the smaller hematite grain size. The crystallization of hematite and In2O3 was suppressed with the drops of enthalpy values due to the stronger solid-solid interactions after ball milling. These caused gradual In3+-Fe3+ substitution in hematite/In2O3 lattices.

The Mössbauer Spectrum Research of the Lanthanon Compound R3Fe29-xCrX

We have systemically investigated mössbauer spectrum of R3Fe29-xCrx (R=Y, Gd, Tb, Dy) compound. Isomer shift、Quadrupole split and Hyperfine field at room temperature are studied. We know that the electronics transfer occurs between R and Fe atoms in the R3Fe29-xCrx compound.

The Mössbauer Spectrum Research of the Lanthanon Compound Tb3Fe29-xCrx

A systematic investigation on the isomer shift, quadrupole split, hyperfine field and the preferential occupation of Cr atom of the crystal site at different temperatures of the novel compounds Tb3Fe29-xCrx (x=1.0,1.2,2.0,3.0)has been performed. Our research method is to use ATOM process to protract the crystal site structure map and every sit near neighbor configuration map of the Tb3Fe26.0Cr3.0, and calculate the bond length of neighboring atoms. At the base of the careful research of the Tb3Fe26.0Cr3.0 crystal structure, we establish the Mössbauer Spectroscopy fitting program.The result of the research indicates that the Cr substitutes the Fe in 4i crystal site priority when the content of the Cr atom in the Tb3Fe29-xCrx is x=1.0, 1.5, the Cr substitutes the Fe in 8j crystal site priority when the content of Cr atom is x=2.0, 3.0, Tb3Fe29-xCrx hyperfine field reduces as x adds up from 1.0 to 3.0.

Quadrupole Splitting and Paramagnetic Iron Core Structure in Iron-Dextran Complexes: A Mössbauer Effect Study

The pharmaceutical^ important iron-dextran complexes (ferritin models) were studied by Mössbauer spectroscopy in frozen solution at 87 K and in lyophilized form at 297 and 87 K. The quadrupole splittings of the lyophilized forms of iron-dextran complexes measured at 297 and 87 K were slightly different. The quadrupole splittings of several complexes in lyophilized form and frozen solutions measured at 87 K were also different. Slight differences in the quadrupole split-ting were found for various iron-dextran complexes. Mössbauer spectra of iron-dextran complexes were better fitted using two quadrupole split doublets. Slight differences in the corresponding quadrupole splittings and doublet ratios were observed for various complexes.