Y2O3:Eu and the Mössbauer isomer shift coefficient of Eu compounds from ab-initio simulations

We report on a full potential density functional theory characterization of Y2O3 upon Eu doping on the two inequivalent crystallographic sites 24d and 8b. We analyze local structural relaxation,electronic properties and the relative stability of the two sites. The simulations are used to extract the contact charge density at the Eu nucleus. Then we construct the experimental isomer shift versus contact charge density calibration curve, by considering an ample set of Eu compounds : EuF3, EuO,EuF2, EuS, EuSe, EuTe, EuPd3 and the Eu metal. The, expected, linear dependence has a slope of α= 0.054 mm/s/Å3, which corresponds to nuclear expansion parameter ∆R/R= 6.0·10−5.αallows to obtain an unbiased and accurate estimation of the isomer shift for any Eu compound. We test this approach on two mixed-valence compounds Eu3S4 and Eu2SiN3, and use it to predict theY2O3:Eu isomer shift with the result +1.04 mm/s at the 24d site and +1.00 mm/s at the 8b site.

Study of Structural, Magnetic, and Mossbauer Properties of Dy2Fe16Ga1−xNbx (0.0 ≤ x ≤ 1.0) Prepared via Arc Melting Process

Intermetallic compounds of Dy2Fe16Ga1−xNbx (x = 0.0 to 1.00) were synthesized by arc melting. Samples were investigated for structural, magnetic, and hyperfine properties using X-ray diffraction, vibration sample magnetometer, and Mossbauer spectrometer, respectively. The Rietveld analysis of room temperature X-ray diffraction data shows that all the samples were crystallized in Th2Fe17 structure. The unit cell volume of alloys increased linearly with an increase in Nb content. The maximum Curie temperature Tc ~523 K for x = 0.6 sample is higher than Tc = 153 K of Dy2Fe17. The saturation magnetization decreased linearly with increasing Nb content from 61.57 emu/g for x = 0.0 to 42.46 emu/g for x = 1.0. The Mössbauer spectra and Rietveld analysis showed a small amount of DyFe3 and NbFe2 secondary phases at x = 1.0. The hyperfine field of Dy2Fe16Ga1−xNbx decreased while the isomer shift values increased with the Nb content. The observed increase in isomer shift may have resulted from the decrease in s electron density due to the unit cell volume expansion. The substantial increase in Tc of thus prepared intermetallic compounds is expected to have implications in magnets used for high-temperature applications.

MÖSSBAUER SPECTROSCOPY OF FERROUS FUMARATE IN PHARMACEUTICAL PRODUCT USED TO TREAT ANEMIA

The World Health Organization (WHO) considers iron deficiency anemia a serious public health problem in developing countries and recommends the use of iron tablets containing iron II for prevention and treatment. The results of Mössbauer measurements of the drug “Ferretab”, which is widely used in medicine for the treatment and prevention of iron deficiency anemia, are presented. This drug contains fumarate iron, C4H2FeO4, and has a small amount of folic acid. In this paper, the temperature dependence of isomer shift and quadrupole splitting values of 57Fe nuclei in iron fumarate were studied. The measurements show that when the temperature increases, the isomer shift and quadrupole splitting of 57Fe nuclei in iron fumarate decreases, the decrease in the isomer shift value is associated with the second-order Doppler effect. Based on Mössbauer measurements, the Debye temperature of this drug was determined. The Debye temperature gives us information about the strong bonding of 57Fe atoms with the environment. A high temperature value means a strong bond and vice versa, a small temperature value means a bond with low rigidity. The coupling constant (Debye temperature) defined for “Ferretab” iron nuclei has been compared with different Debye temperatures found in previous studies on some iron deficiency anemia drugs. Additionally, the values were compared with various clinical studies conducted in in-vivo and in-vitro for comparison of the efficacy of some of the most commonly used drugs to treat and prevent iron deficiency anemia. According to these comparisons, it was established a possible relationship between the Debye temperature of the iron atoms of the drugs under study and their effectiveness. It was noted that the lower the Debye temperature of iron atoms of the drug, the more iron absorbs the human body.

A 119Sn Mössbauer-spectroscopic characterization of the diamagnetic birefringence material Sn2B5O9Cl

The crystal structure of diamagnetic borate chloride Sn2B5O9Cl exhibits two crystallographically independent tin sites which both show pronounced lone-pair activity of the tin atoms. This is reflected in substantial quadrupole splitting in the 119Sn Mössbauer spectrum. The isomer shifts of 3.887(8) and 4.137(7) mm s−1 clearly indicate divalent tin. In agreement with bond valence calculations, the Sn1 atoms have a lower charge and the higher isomer shift, compatible with a higher electron density at the tin nuclei.

Separation of hyperfine interactions in Mössbauer spectrocsopy

Problem of determination of isomer shift, all components of the electric field gradient and hyperfine magnetic field in case of mixed hyperfine interactions is presented. Orientation of hyperfine fields in the absorber Cartesian frame can be determined by few measurements with use of unpolarized radiation under different directions of wave vector with respect to the absorber. The method can be applied for absorbers with well separated absorption lines in their spectra. Explicit formulas for tensor components of hyperfine interactions derived from velocity moments formalism are presented.

Zero-Dimensional Graphene and Its Behavior under Mechanochemical Activation with Zinc Ferrite Nanoparticles

ABSTRACTEquimolar mixtures of zero-dimensional graphene (SkySpring Nanomaterials, 1-5 nm particle size) and zinc ferrite nanoparticles (Alfa Aesar, 50 nm particle size) were exposed to mechanochemical activation by high-energy ball milling for time intervals of 0-12 hours. Their structural and magnetic properties were analyzed by Mӧssbauer spectroscopy and magnetic measurements. The spectra of zinc ferrite milled without graphene were fitted with one quadrupole-split doublet (quadrupole splitting 0.5 mm/s, isomer shift 0.23 mm/s) and indicated that zinc ferrite was superparamagnetic. The line width of the doublet increased from 0.41 to 0.64 mm/s, which correlates with a reduction in particle size as effect of the ball milling processing performed. When graphene was added to the milling powders, the Mӧssbauer spectra showed the appearance of another quadrupole doublet, with a quadrupole splitting of 0.84 mm/s and an isomer shift of -0.38 mm/s. Its abundance to the spectrum remained constant to 4.48% while the milling time was increased. This second doublet could be related to carbon atoms occupying neighborhoods in the proximity of iron atoms. Hysteresis loops were recorded in an applied magnetic field of 5 T at a temperature of 5 K. A change in the approach to saturation of the loop was observed, with saturation being achieved for the sample milled for 12 hours with graphene. Zero-field-cooling-field-cooling (ZFC-FC) was performed on all samples between 5-300 K with an applied magnetic field of 200 Oe. Graphene was found to stabilize the magnetic properties of the milled system of powders to a blocking temperature of about 90 K.