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AAuAl (A = Ca, Sc, and Ti): Peierls Distortion, Atomic Coloring, and Structural Competition
Joyce Pham1, Gordon J Miller1,2
1Department of Chemistry , Iowa State University , Ames , Iowa 50011-3111 , United States.
Inorganic Chemistry
|March 17, 2018
Summary
The crystal structure of AAuAl compounds (A = Ca, Sc, Ti) varies with electronic structure and atomic size. This variation is driven by maximizing gold-aluminum contacts and influenced by chemical pressure effects.
Area of Science:
- Solid State Chemistry
- Computational Materials Science
- Crystallography
Background:
- The interplay between electronic structure, atomic radii, and crystal symmetry is crucial for understanding intermetallic compound formation.
- Ternary intermetallic compounds like AAuAl exhibit diverse crystal structures influenced by constituent element properties.
Purpose of the Study:
- To investigate the correlation between crystal structure variations in AAuAl (A = Ca, Sc, Ti) and their underlying electronic structures.
- To elucidate the role of atomic size, valence electron count, and site preference in determining the preferred crystal symmetries.
- To analyze the influence of chemical pressure on structural transitions and understand the electronic origins of specific crystal phases.
Main Methods:
- Density Functional Theory (DFT) calculations were employed to model the electronic and structural properties of AAuAl compounds.
- Total energy versus volume calculations were performed to evaluate the effect of chemical pressure on structural stability.
- Analysis of nearest neighbor contacts and site occupancies for Au and Al atoms was conducted.
Main Results:
- Crystal structure transitions from orthorhombic Co2Si-type to hexagonal Fe2P-type and Ni2In-type were observed and correlated with electronic structures and valence electron counts.
- The size of the 'A' metal (Ca, Sc, Ti) and site preferences of Au and Al atoms significantly influence the crystal structure, favoring maximized Au-Al contacts.
- Larger unit cell volumes favor the orthorhombic structure, while smaller volumes promote hexagonal structures, consistent with chemical pressure effects.
- The Mg2Ga-type structure of ScAuAl, a distorted Fe2P-type supercell, is attributed to a Peierls-type distortion mechanism in Au chains.
Conclusions:
- The crystal structure of AAuAl compounds is intricately linked to electronic configurations, atomic sizes, and the drive for optimal bonding.
- Chemical pressure, modulated by the varying 'A' metal, acts as a key factor in dictating the observed structural phase transitions.
- DFT provides a robust framework for predicting and understanding structure-property relationships in complex intermetallic systems.
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