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Rhombohedral Distortion of the Cubic MgCu2-Type Structure in Ca2Pt3Ga and Ca2Pd3Ga

TitleRhombohedral Distortion of the Cubic MgCu2-Type Structure in Ca2Pt3Ga and Ca2Pd3Ga
Publication TypeJournal Article
Year of Publication2018
AuthorsToombs, A, Miller, GJ
JournalCrystals
Volume8
Pagination186
Date Published05
Type of ArticleArticle
ISBN Number2073-4352
Accession NumberWOS:000435192500005
Keywordsband structure, brillouin-zone integrations, catalyst, chemistry, coloring problem, Crystallography, diffraction, Electronic structure, Intermetallics, laves, Materials Science, metals, phase, platinum, polar, stability, structure optimizations, ternary Laves phases, total energy, valence electron-concentration, x-ray
Abstract

Two new fully ordered ternary Laves phase compounds, Ca2Pt3Ga and Ca2Pd3Ga, have been synthesized and characterized by powder and single-crystal X-ray diffraction along with electronic structure calculations. Ca2Pd3Ga was synthesized as a pure phase whereas Ca2Pt3Ga was found as a diphasic product with Ca2Pt2Ga. Electronic structure calculations were performed to try and understand why CaPt2 and CaPd2, which crystalize in the cubic MgCu2-type Laves phase structure, distort to the ordered rhombohedral variant, first observed in the magneto-restricted TbFe2 compound, with the substitution of twenty-five percent of the Pt/Pd with Ga. Electronic stability was investigated by changing the valence electron count from 22e(-)/f.u. in CaPd2 and CaPt2 (2x) to 37e(-)/f.u. in Ca2Pd3Ga and Ca2Pt3Ga, which causes the Fermi level to shift to a more energetically favorable location in the DOS. The coloring problem was studied by placing a single Ga atom in each of four tetrahedra of the cubic unit cell of the MgCu2-type structure, with nine symmetrically inequivalent models being investigated. Non-optimized and optimized total energy analyses of structural characteristics, along with electronic properties, will be discussed.

DOI10.3390/cryst8050186
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