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.
Highlights
Platinum exhibits the second largest relativistic contraction of the 6s orbitals, second only toAu [1], and has interesting catalytic properties, making it an interesting metal to study, especially in reduced environments
Electronic structure calculations to obtain density of states (DOS) and crystal orbital Hamilton population (COHP) curves for bonding analysis were performed on CaM2 and Ca2 M3 Ga (M = Pd, Pt) using the Stuttgart Tight-Binding, Linear-Muffin-Tin
As Pt dissolves into the liquid, we hypothesize that the presence of Ag slows the reaction rate between Ca and Pt to form CaPt2 and allows Pt and Ga to achieve sufficient mixing in the liquid before crystallizing into Ca2 Pt3 Ga
Summary
Platinum exhibits the second largest relativistic contraction of the 6s orbitals, second only toAu [1], and has interesting catalytic properties, making it an interesting metal to study, especially in reduced environments. Exploration of the Ca-Pt-X (X = Ga, In) system revealed a new ternary compound, Ca2 Pt3 Ga, which turned out to be an ordered rhombohedral distortion of the MgCu2 -type. Laves phases are the largest class of intermetallic compounds with the general formula AB2. Binary Laves phases primarily crystalize in one of three crystal structures: MgCu2 , MgZn2 , or. These structure types, which appear in a vast number of intermetallic systems, contain topologically closed-packed Frank–Kasper polyhedra and have been intensely studied for magnetic and magnetocaloric properties, hydrogen storage, and catalytic behavior [3,4,5,6,7,8,9]. The stability of Laves phases has been described by using geometrical and electronic structure factors. Geometrical factors include packing densities and atomic size ratios of A/B whereas electronic factors include valence electron count (vec) and difference in electronegativities between A and B [10,11]
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