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Magnetic Characterization: Instruments and Methods
Published in Jeffrey N. Anker, O. Thompson Mefford, Biomedical Applications of Magnetic Particles, 2020
The electric quadrupole splitting depends upon the non-radially symmetric electrons (i.e. non s-shell electrons) producing an electric field gradient. For example, assume that the Fe57 atom is located at the center of a regular octahedron (a typical configuration). If the six nearest neighbor atoms are identical, the electric field gradient is zero. If the lattice is distorted either through pressure or temperature changes, or if different atoms with different charge configurations occupy the nearest neighbor positions, then we have changed the electric field gradient seen by Fe57 atom. This electric field gradient splits a single state into two, producing a doublet in the Mossbauer spectrum (Figure 5.7). Specifically, Fe57 has an excited state with an angular quantum number I of 3/2. Therefore, changes in the electric field gradient split the 3/2 to 1/2 transition into two spin substates: mI = ±1/2 and mI = ±3/2. This separation between the states can be used to measure the sign and magnitude of this electric field gradient.
Nuclear Radiation
Published in Mircea S. Rogalski, Stuart B. Palmer, Quantum Physics, 2020
Mircea S. Rogalski, Stuart B. Palmer
We see that EQ=0 for and the two-level splitting illustrated in Figure 12.8 (d) corresponds to the first excited state of , with (see Figure 12.7 (b)). The quadrupole splitting is a measure of the asymmetry of the electron charge distribution around the iron nucleus, such that the larger is the splitting of the two-line pattern, the larger is the local distortion from cubic symmetry.
Charge transfer of CsMnFe-Prussian blue analogue induced by pressure and temperature
Published in Phase Transitions, 2022
Qinghang Zhang, Jiajun Mo, Yimin Xie, Yanfang Xia, Min Liu
Figure 2 shows the room temperature Mössbauer spectra for different pressure treatments fitted with the least squares method. The values of isomer shift (IS), quadrupole splitting (QS) and line width (Γ) are displayed in Table 1. Quadrupole splitting represents the diversion of the electron cloud sphere symmetry. There is no quadrupole splitting since the nuclear charge distribution in the singlet is located at the centre of the symmetric octahedral CN ligand coordination sphere. The 3d electrons of the Fe ions in FeC6 unit are all located in t2g orbitals by the crystal field. In the case of the FeII ion, there are six electrons in its 3d shell layer with fully filled t2g orbitals, forming a spherical row of charge distribution. And one less electron in the t2g orbital of the FeIII ion creates a sizable electric field gradient where the nucleus is located. This allows the singlet and doublet observed in Figure 2 to be attributed to structures FeIILS-CN-MnIIIHS and FeIIILS-CN-MnIIHS, respectively. The sample treated with 0 Mpa pressure consists of a singlet with IS = 0.007 mm/s (32.5%) and a doublet with IS = −0.011, QS = 0.144 (67.5%). At this point both FeIII-CN-MnII and FeII-CN-MnIII microstructures exist in CsMn[Fe (CN)6]·xH2O samples.
2D ferrous nitroprussides stabilized through organic molecules as pillars: preparation, crystal structure and related properties
Published in Journal of Coordination Chemistry, 2021
Y. Avila, J. Rodríguez-Hernández, P. M. Crespo, M. González M., E. Reguera
Mössbauer spectra of iron-containing solids provide information on the valence and electronic configuration of the iron ion but also inform us of fine structural details for the sample under study. Such information is close to that expected under thermodynamic equilibrium because the spectra recording usually takes several hours, in some cases days, and it results from the accumulation of a large number of scans in terms of the γ-rays energy modulation through the source velocity by the Doppler effect. This explains why we are using Mössbauer spectroscopy in this study as a source of complementary structural information but also to explore the possibility of occurrence of a spin transition induced by a temperature change in the sample, an effect already observed for pyridine and its derivatives [12–14]. For this reason, the spectra were recorded at 295 and 5 K; first on the sample cooling and then on its heating. The obtained spectra were fitted as a superposition of quadrupole splitting doublets (Figures 6 and S18–S23). The values for the Mössbauer parameters, isomer shift (δ, in mm/s), quadrupole splitting (Δ, in mm/s), linewidth (Γ, in mm/s) and relative area (A, in %), derived from that fitting process are summarized in Table 4. The values of δ are reported relative to sodium nitroprusside at room temperature. The isomer shift parameter is an excellent sensor for the valence and electronic configuration for the iron ion, and also sheds light on the bonding properties of its first neighbors (ligands), and of the coordination number. The value of Δ results from the interaction of the nuclear quadrupole moment (Q) with the electric field gradient (∇E) sensed by the iron nucleus. Two factors contribute to the value of ∇E, the presence of unpaired electrons in the atoms, and the charge asymmetry due to its first neighbors (ligands). The value of Γ sheds light on small changes on the local interactions that determine the values of δ and Δ for a given structural site.