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MnCoGe-based materials have the potential to exhibit giant magnetocaloric effects due to coupling between magnetic ordering and a martensitic phase transition. Such coupling can be realized by matching the temperatures of the magnetic and structural phase transitions. To understand the site preference of different elements and the effect of hole or electron doping on the stability of different polymorphs of MnCoGe, crystal orbital Hamilton population (COHP) analysis has been employed for the first time to evaluate peculiarities of chemical bonding in this material. The shortest Mn–Mn bond in the structure is found to be pivotal to the observed ferromagnetic behavior and structural stability of hexagonal MnCoGe. Based on this insight, eliminating anti-bonding features of the shortest Mn-Mn bond at the Fermi energy is proposed as a feasible way to stabilize the hexagonal polymorph, which is then realized experimentally by substitution of Zn for Ge. The hexagonal MnCoGe structure is stabilized due to depopulation of the anti-bonding states and strengthening of the Mn–Mn bonding. This change in chemical bonding leads to anisotropic evolution of lattice parameters. The structural and magnetic properties of Zn-doped MnCoGe have been elucidated by synchrotron X-ray diffraction and magnetic measurements, respectively.
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Chemical Bonding and the Role of Node-Induced Electron Confinement
The chemical bond is the cornerstone of chemistry, providing a conceptual framework to understand and predict the behavior of molecules in complex systems. However, the fundamental origin of chemical bonding remains controversial, and has been responsible for fierce debate over the past century. Here we present a unified theory of bonding, using a separation of electron delocalization effects from orbital relaxation to identify three mechanisms -- node-induced confinement (typically associated with Pauli repulsion, though more general), orbital contraction and polarization -- that each modulate kinetic energy during bond formation. Through analysis of a series of archetypal bonds, we show that an exquisite balance of energy-lowering delocalizing and localizing effects are dictated simply by atomic electron configurations, nodal structure and electronegativities. The utility of this unified bonding theory is demonstrated by its application to explain observed trends in bond strengths throughout the periodic table, including main group and transition metal elements.
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- Award ID(s):
- 2313791
- PAR ID:
- 10539298
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Journal of the American Chemical Society
- Volume:
- 146
- Issue:
- 14
- ISSN:
- 0002-7863
- Page Range / eLocation ID:
- 9532 to 9543
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/jacs.3c10633
