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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
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Higher Dimensionality in the Mg-Co-B System: Synthesis and Structure of Incommensurate Composite Mg1+εCo4B4
Paul Oftedahl1, Gourab Bhaskar1, Nawsher J Parvez2
1Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States.
Journal of the American Chemical Society
|December 10, 2025
Summary
Researchers discovered and synthesized Mg1+εCo4B4, an incommensurate composite crystal. This new material, Mg1+εCo4B4, shows no magnetic ordering or superconductivity down to 5 K.
Area of Science:
- Solid State Chemistry
- Materials Science
- Crystallography
Background:
- Incommensurate composite crystals exhibit unique structural properties due to mismatched lattice periodicities.
- The Nd1+εFe4B4 structure type is known for its complex, incommensurate nature.
Purpose of the Study:
- To discover and synthesize a new Mg-Co-B compound.
- To characterize the crystal structure and magnetic properties of the novel Mg1+εCo4B4.
- To refine a superspace symmetry model for this incommensurate composite compound.
Main Methods:
- High-temperature in situ X-ray diffraction for synthesis and initial characterization.
- Neutron powder diffraction and high-resolution powder X-ray diffraction for detailed structural refinement.
- Scanning transmission electron microscopy and electron diffraction for structural confirmation.
- Density Functional Theory (DFT) calculations for theoretical analysis of magnetic properties and stability.
Main Results:
- Successful synthesis and discovery of Mg1+εCo4B4 (ε ≈ 0.272) using a MgH2 precursor.
- Refined crystal structure in a (3 + 1)-dimensional superspace model (P42/ncm(00γ)s00s) with Mg occupying the rare-earth site.
- Magnetic measurements and DFT calculations indicate no long-range magnetic ordering or superconductivity down to 5 K.
- Confirmed that Mg1+εCo4B4 is not a hydrogen-stabilized phase.
Conclusions:
- Mg1+εCo4B4 is the second reported compound in the Mg-Co-B system.
- This work presents the first superspace symmetry model of a Nd1+εFe4B4-type incommensurate composite refined from powder diffraction data.
- The compound exhibits interesting structural complexity without magnetic ordering or superconductivity at low temperatures.
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