Fe-Ga rare earth elements
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Fe-Ga Rare Earth Elements: Insights from Recent Research
Atomic Ordering and Anelasticity in Fe-Ga-RE Alloys
Thermally Activated Effects and Phase Transitions
Research on Fe-(16-21)at% Ga-RE (rare earth elements such as La, Tb, Dy, Er, Yb) alloys has revealed significant insights into their atomic ordering and anelastic properties. Studies have identified two thermally-activated and two transient effects in these alloys. These phenomena are linked to structural and phase transitions, particularly the D03 ordering of rapidly cooled alloys with the A2 structure at around 300°C and disordering at around 500°C for annealed samples. These findings were supported by neutron diffraction, vibrating sample magnetometry, and positron annihilation experiments.
Stress-Induced Reorientation and Atomic Jumps
The thermally activated transitory effects observed in these alloys are tentatively explained by stress-induced reorientation of Ga-Ga pairs, vacancy-vacancy pairs, and carbon atom jumps. This understanding is crucial for developing applications that rely on the mechanical properties of these materials.
Enhancing Magnetostriction in Fe-Ga Alloys with Rare Earth Doping
Ce-Doping and Melt-Spinning Techniques
To improve the magnetostrictive properties of Fe-Ga alloys, researchers have explored the effects of doping with rare earth elements like Ce and employing melt-spinning techniques. The introduction of Ce into Fe83Ga17 alloys and subsequent melt-spinning resulted in the formation of the CeGa2 phase and an asymmetrical DO3 phase. These structural changes significantly enhanced the magnetostriction of the alloys, with the melt-spun Fe83Ga17Ce0.8 alloy showing the highest magnetostriction, followed by the as-cast Fe83Ga17Ce0.8 alloy, and then the as-cast Fe83Ga17 alloy.
Mechanisms Behind Enhanced Magnetostriction
The enhanced magnetostriction is attributed to the formation of new phases and the preferred orientation along the (100) direction. This insight is valuable for designing Fe-Ga alloys with superior magnetostrictive properties for various technological applications.
Origin of Large Magnetostrictive Properties in Rare Earth Doped Fe-Ga Alloys
Controversy and Resolution
The origin of the large magnetostrictive properties in rare earth-doped Fe-Ga alloys has been a subject of debate. Some researchers attribute it to the distortion of the A2 lattice, while others believe it is due to the formation of (0 0 1) oriented textures. Recent studies have clarified that the increase in magnetostrictive properties is closely related to whether the rare earth elements enter the A2 crystal lattice. When rare earth elements do not enter the A2 lattice, the large magnetostriction is mainly due to (0 0 1)-oriented columnar crystals. Conversely, when rare earth elements enter the A2 lattice, the large magnetostriction is primarily due to residual stress or lattice distortion, with (0 0 1)-oriented columnar crystals playing a secondary role.
Rare Earth Elements in Precambrian Fe Formations
REE Systematics and Marine Redox Conditions
The study of rare earth element (REE) compositions in Archean and Paleoproterozoic Fe formations has provided new perspectives on the significance and mechanisms of deposition. Analyses of Fe formation samples from 3.0 to 1.8 billion years ago reveal temporal trends in REE and Y patterns that reflect shifts in marine redox conditions. Archean Fe formations generally lack significant shale-normalized negative Ce anomalies, while those younger than 1.9 Ga display prominent positive Ce anomalies. These differences suggest varying REE cycling in the water column, with late Paleoproterozoic Fe formations recording evidence of a metal and Ce oxide shuttle across the redoxcline from oxic shallow seawater to deeper anoxic waters.
Implications for Fe Oxidation Mechanisms
The absence of REE Y patterns indicative of an oxide shuttle in Archean Fe formations implies a lack of a distinct Mn redoxcline before the rise of atmospheric oxygen. This finding challenges classical models that invoke oxidation by free oxygen and supports the idea that metabolic Fe oxidation, possibly controlled by microbial activity, was a more likely mechanism for Fe formation deposition in the Archean ocean.
Conclusion
The integration of rare earth elements into Fe-Ga alloys significantly enhances their magnetostrictive properties and provides valuable insights into their atomic ordering and phase transitions. Additionally, the study of REE compositions in ancient Fe formations offers a deeper understanding of the marine redox conditions and Fe oxidation mechanisms in the early Precambrian. These findings have important implications for both material science and our understanding of early Earth environments.
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