Effects of composition and pressure on electronic states of iron in bridgmanite

Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mössbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mössbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10–50% Fe/total cations, 0–25% Al/total cations, 12–100% Fe3+/total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe3+ provide a Mössbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at ~70 GPa. Thus center shift can easily distinguish Fe3+ from Fe2+ at high pressure, which exhibits two distinct Mössbauer sites with center shift ~1 mm/s and quadrupole splitting 2.4–3.1 and 3.9 mm/s at ~70 GPa. Correct quantification of Fe3+/total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. In Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to ~20% of the Fe may be a Fe2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.

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.

Особенности магнитной структуры поликристаллов Y-=SUB=-3-=/SUB=-Fe-=SUB=-5-=/SUB=-O-=SUB=-12-=/SUB=-, синтеризованных методом радиационно-термического спекания

The Mössbauer spectroscopy (MS) method was used to study polycrystalline iron yttrium garnet (YIG) samples synthesized by radiation thermal sintering (RTS) technology and by standard ceramic technology (CT). The best option for decomposing the MS spectra of the objects of study was selected, which is a model of the experimental spectrum with five sextets. An additional fifth sextet is caused by Fe3 + ions, surrounded by oxygen vacancies which lead to distortion of the Fe tetrahedra which reflected by an increase in the quadrupole splitting of Fe3+. An increase in the density of s-electrons on Fe ions in distorted tetrahedra lead to a decrease in the isomeric chemical shift δ of Fe ions up to a values closed to the δ value for Fe4+ ions. It was shown that the optimal crystalline structure realizes for Y3Fe5O12 polycrystals upon sintering by RTS method in the temperature range of 1350–1400 ° C for a time from 40 to 60 min.

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.

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.