A review of the systematic Mossbauer studies on the most encountered iron oxides and hydroxides is given in which the qualitative and quantitative aspects, helpful in the characterization of natural smaples, are emphasized. The present possibilities of Mossbauer spectroscopy in soil characterization are further illustrated from some examples of natural soils.

Some aspects concerning the characterization of iron oxides and hydroxides in soils and clays

${\text{SnO}}_{2}$ nanoparticles doped with Fe of different concentrations were synthesized by a chemical coprecipitation method. After calcination at $600\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, the samples were characterized using x-ray diffraction (XRD), transmission electron microscope (TEM), and superconducting quantum interference device magnetometer. XRD shows that the solubility of Fe in ${\text{SnO}}_{2}$ (${\text{Sn}}_{1\ensuremath{-}x}{\text{Fe}}_{x}{\text{O}}_{2}$: primary phase where Fe substitutes Sn in ${\text{SnO}}_{2}$ matrix) is less than 7.5% $(xl0.075)$ and ${\text{Fe}}_{2}{\text{O}}_{3}$ (hematite) or ${({\text{Fe}}_{1\ensuremath{-}y}{\text{Sn}}_{y})}_{2}{\text{O}}_{3}$ (where Sn substitutes Fe in ${\text{Fe}}_{2}{\text{O}}_{3}$ matrix) is evolved as a secondary phase for $x\ensuremath{\ge}0.075$ along with ${\text{Sn}}_{1\ensuremath{-}x}{\text{Fe}}_{x}{\text{O}}_{2}$ (primary phase). TEM shows that the particles are crystalline and of size in the nanometric regime $(10\ifmmode\pm\else\textpm\fi{}3\text{ }\text{nm})$. The $M(T)$ and $M(H)$ studies indicated an antiferromagnetic (AFM) interaction in 3% and 5% (atomic weight) Fe-doped ${\text{SnO}}_{2}$ nanoparticles. The observed AFM interaction can be explained by the bound magnetic polaron model for insulating diluted magnetic semiconductor systems. It is seen that the strength of AFM interaction reduces with increase in doping concentration. On the other hand, 7.5% Fe-doped ${\text{SnO}}_{2}$ nanoparticles show the ferromagnetic interaction, but the origin of the observed ferromagnetism is identified due to the presence of ${({\text{Fe}}_{1\ensuremath{-}y}{\text{Sn}}_{y})}_{2}{\text{O}}_{3}$ as a secondary phase.

Structure and magnetism of Fe-doped SnO 2 nanoparticles

In recent years, hematite's potential as a photoanode material for solar hydrogen production has ignited a renewed interest in its physical and interfacial properties, which continues to be an active field of research. Research on hematite photoanodes provides new insights on the correlations between electronic structure, transport properties, excited state dynamics, and charge transfer phenomena, and expands our knowledge on solar cell materials into correlated electron systems. This research news article presents a snapshot of selected theoretical and experimental developments linking the electronic structure to the photoelectrochemical performance, with particular focus on optoelectronic properties and charge carrier dynamics.

The "Rust" Challenge: On the Correlations between Electronic Structure, Excited State Dynamics, and Photoelectrochemical Performance of Hematite Photoanodes for Solar Water Splitting.

[1] A major disparity is observed between the late Paleozoic-early Mesozoic apparent polar wander paths (APWPs) of Laurussia and Gondwana when the landmasses are re-assembled in a conventional “A-type” Pangea. This discrepancy has endured from the earliest paleomagnetic reconstructions of the supercontinent, and has prompted discussions of non-dipole paleomagnetic fields and alternative paleogeographic models. Here we report on a joint paleomagnetic-geochronologic study of Late Permian and Early to Middle Triassic volcanic and volcaniclastic rocks from Argentina, which demonstrates support for an A-type model, without requiring modification to the geocentric axial dipole hypothesis. New SHRIMP U-Pb and 40Ar-39Ar isotopic dating has reinforced the inferred age of the sequences, which we estimate at ∼264 Ma (Upper Choiyoi Group) and ∼245 Ma (Puesto Viejo Group). Field-stability tests demonstrate that the volcanic rocks are carrying early/primary magnetizations, which yield paleopoles: 73.7°S, 315.6°E, A95: 4.1°, N: 40 (Upper Choiyoi) and 76.7°S, 312.4°E, A95: 7.3°, N: 14 (Puesto Viejo). A comprehensive magnetic fabric analysis is used to evaluate structural restorations and to correct for magnetization anisotropy. The paleomagnetic results derived from volcaniclastic rocks are interpreted to be affected by inclination shallowing, and corrections are discussed. A comparison of these new results with the existing Permian-Triassic paleomagnetic data from Gondwana suggests the presence of widespread bias in the latter. We contend that such bias can explain the observed APWP disparity, at least for Late Permian-Middle Triassic time, and that alternative paleogeographic reconstructions or non-dipole paleomagnetic fields do not need to be invoked to resolve the discrepancy.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JB008495

Support for an “A‐type” Pangea reconstruction from high‐fidelity Late Permian and Early to Middle Triassic paleomagnetic data from Argentina

Iron being the fourth most abundant element in the earth crust, 57Fe Mossbauer spectroscopy has become a suitable additional technique for the characterization of all kind of soil materials and minerals. However, for that purpose a good knowledge of the spectral behavior of the various minerals is indispensable. In this chapter a review of the most important soil materials and rock-forming minerals is presented. It starts with a description of the Mossbauer spectroscopic features of the iron oxides and hydroxides, which are essentially present in soils and sediments. Further, the Mossbauer spectra from sulfides, sulfates and carbonates are briefly considered. Finally, the Mossbauer features of the typical and most common silicate and phosphate minerals are reported. The chapter ends with some typical examples, illustrating the use and power of Mossbauer spectroscopy in the characterization of minerals.

Application of Mössbauer Spectroscopy in Earth Sciences

A Mossbauer spectroscopic study is reported on a series of titanium-substituted hematites, (Fe1-xTix)2O3 with x < 0025 It is found that, even in powder samples, Ti influences the Morin transition (TM) quite strongly One percent of Ti is enough to depress TM below 10 K and this is likely true for a homogeneous sample with 05% of Ti too The magnetic ordering temperature lowers with Ti-content

https://iopscience.iop.org/article/10.1088/0031-8949/33/1/013/pdf

B K Srivastava

Papers

Morin-Transition in Ti-Substituted Hematite: A Mössbauer Study