Synergistic Geometrical and Electronic Features in the Intermetallic Phases Ca2AgM2, Ca2MgM2, and Ca2GaM2 (M = Pd, Pt)

Ponou, Siméon; Miller, Gordon J.

doi:10.1002/zaac.201500090

Cited by 9 publications

(28 citation statements)

References 45 publications

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“…Dirac feSM candidate Ca 2 Pt 2 Ga.-We begin by discussing the best Dirac feSM candidate we found: the intermetallic compound Ca 2 Pt 2 Ga, which was reported to crystalize in the Ca 2 Ir 2 Si-type structure in Ref. [34] (Fig. 2a).…”

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confidence: 98%

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Topological materials discovery using electron filling constraints

Chen

Neaton

et al. 2017

Nature Phys

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Nodal semimetals, materials systems with nodal-point or -line Fermi surfaces, are much sought after for their novel transport and topological properties. Identification of experimental materials candidates, however, has mainly relied on exhaustive database searches. Here we show how recent studies on the interplay between electron filling and nonsymmorphic space-group symmetries can guide the search for nodal semimetals which are 'filling-enforced'. We recast the previously-derived constraints on the allowed electron fillings for band insulators in the 230 space groups into a new form, which enables effective screening of materials candidates based solely on their (1) space group, (2) electron count in the formula unit, and (3) multiplicity of the formula unit. This criterion greatly reduces the computation load for discovering topological materials in a database of previously-synthesized compounds. Of the more than 30,000 entires listed in a few selected nonsymmorphic space groups, our filling criterion alone eliminates 96% of the entries before they are passed on for further analysis. From this guided search, we discover a handful of candidates, including the monoclinic crystals Ca2Pt2Ga, AgF2, and Ca2InOsO6, and the orthorhombic crystal CsHg2. Based on ab initio calculations, we show that these materials have filling-enforced Dirac nodes near the Fermi energy. In addition, we also identify CaPtGa as a promising filling-enforced Dirac-ring semimetal candidate. arXiv:1611.06860v2 [cond-mat.mtrl-sci]

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“…39,40 We use a plane wave cutoff of 280 eV and a k-point grid for BZ integrations of 12 × 12 × 8. Experimental structural data 34 is used. From the projected density of states, we find that the character of the Ca 2 Pt 2 Ga band structure near the Fermi energy has contributions from all three atomic species (Fig.…”

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confidence: 99%

Topological materials discovery using electron filling constraints

Chen

Neaton

et al. 2017

Nature Phys

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“…12 Recently, some ternary phases with the formulation R2M2X with divalent 'active' metals (R = Ca, Sr and Eu) and noble metals of the platinum group (M = Pd, Ir, and Pt), started attracting attention as they frequently exhibited polymorphism with often reversible structural phase transition as a function of temperature, external pressure, valence electron count, and even the active metal size. [13][14][15][16][17][18][19][20][21][22][23] The noble metals therein are present in form of linear chains that are either pair-wise distorted or equidistant. They crystallize mainly in three structure types, and their structural selection seems to be governed by three competing factors.…”

Section: Introductionmentioning

confidence: 99%

Europium-rich ternary phases with noble metals Eu2M2X (M = Pd, Pt; X = Al, Ga, Ge, Cd), and their structural relationship to the Laves phase Ca2Pt3Al1–xAgx

Ponou,

Mudring

2024

Preprint

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The combination of divalent Eu with high magnetic moment and strong spin-orbit coupling (SOC) on Pd or Pt atoms in a single substance, makes Eu-Pd/Pt-X ternary phases attractive for materials with exotic physical properties. For that reason, compositions according to Eu2M2X (M = Pd, Pt; X = Al, Ga, Ge, Cd) were explored. X-ray diffraction analyses revealed that the three Pd analogues Eu2Pd2X with X = Al, Ga, and Ge, crystallize isostructural to Ca2Pd2Ge, a ternary ordered variant of the Zr2Al3-type (orthorhombic Fdd2). In contrast, Eu2Pt2Al adopts the Ca2Ir2Si type rival structure (monoclinic C2/c). The two structure types are closely related as they both feature linear chains of the noble metals, with the X atoms bridging the metal chains from adjacent layers. However, a striking difference is noticeable within the metal chains: The Pd linear chains consist of equidistant PdPd atoms (2.96 Å), whereas in the Pt chains are pairwise distorted with alternating shorter (Pt–Pt = 2.80 Å) and longer (2.98 Å) contacts. The pairwise distortion is, at first glance, is attributed to stronger relativistic influence on Pt atom. In addition, Eu2Pt2Cd, adopts the W2CoB2 type, suggesting that the valence electron count (vec) has strong influence in the structure selection. Finally, both Ca2Pd2Ge- and Ca2Ir2Si-type structures are also discussed as defect Laves phases in connection with the newly discovered phase Ca2Pt3Al1–xAgx (x = 0.13(1)) which adopts the TbFe2 type structure (space group R-3m). DFT first principles electronic band structure calculations, conducted on the Ag-free ordered model “Ca2Pt3Al”, suggested that Ag-inclusion is mainly due to geometric factors, while the chemical bonding picture is consistent with a polar intermetallic system.

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“…In this context, PIC Mg 3 Pt was recently identified in the Mg-based core–shell Mg@Pt nano-composite via in situ TEM (transmission electron microscopy), showing a remarkable “hydrogen pump” effect, as it can solubilize H atoms and transfer them, expediting the desorption rate of MgH 2 . However, very little is known regarding the structural or electronic factors behind the extraordinary properties of Mg 3 Pt. , In this context, the relativistic effects on the chemical bonding are of interest − and seem to be important for the excellent performance of Pt alloys as catalysts and hydrogen storage materials, and it is important to gain a deeper knowledge on the electronic structure of such materials. Interestingly, Mg 2 PtSi (Na 3 As-type, or more precisely the related ternary Li 2 CuAs type) is structurally very close to Mg 3 Pt (Cu 3 P type), and the former can be derived from the latter by the substitution of one Mg site by a Si atom.…”

Section: Introductionmentioning

confidence: 99%

Optimization of Chemical Bonding through Defect Formation and Ordering─The Case of Mg₇Pt₄Ge₄

2023

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The new phase Mg7Pt4Ge4 (Mg8□1Pt4Ge4; □ = vacancy) was prepared by reacting a mixture of the corresponding elements at high temperatures. According to single crystal X-ray diffraction data, it adopts a defect variant of the lighter analogue Mg2PtSi (Mg8Pt4Si4), reported in the Li2CuAs structure. An ordering of the Mg vacancies results in a stoichiometric phase, Mg7Pt4Ge4. However, the high content of Mg vacancies results in a violation of the 18-valence electron rule, which appears to hold for Mg2PtSi. First principle density functional theory calculations on a hypothetical, vacancy-free “Mg2PtGe” reveal potential electronic instabilities at E F in the band structure and significant occupancy of states with an antibonding character resulting from unfavorable Pt–Ge interactions. These antibonding interactions can be eliminated through introduction of Mg defects, which reduce the valence electron count, leaving the antibonding states empty. Mg itself does not participate in these interactions. Instead, the Mg contribution to the overall bonding comes from electron back-donation from the (Pt, Ge) anionic network to Mg cations. These findings may help to understand how the interplay of structural and electronic factors leads to the “hydrogen pump effect” observed in the closely related Mg3Pt, for which the electronic band structure shows a significant amount of unoccupied bonding states, indicating an electron deficient system.

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Synergistic Geometrical and Electronic Features in the Intermetallic Phases Ca₂AgM₂, Ca₂MgM₂, and Ca₂GaM₂ (M = Pd, Pt)

Cited by 9 publications

References 45 publications

Topological materials discovery using electron filling constraints

Topological materials discovery using electron filling constraints

Europium-rich ternary phases with noble metals Eu2M2X (M = Pd, Pt; X = Al, Ga, Ge, Cd), and their structural relationship to the Laves phase Ca2Pt3Al1–xAgx

Optimization of Chemical Bonding through Defect Formation and Ordering─The Case of Mg₇Pt₄Ge₄

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Synergistic Geometrical and Electronic Features in the Intermetallic Phases Ca2AgM2, Ca2MgM2, and Ca2GaM2 (M = Pd, Pt)

Cited by 9 publications

References 45 publications

Topological materials discovery using electron filling constraints

Topological materials discovery using electron filling constraints

Europium-rich ternary phases with noble metals Eu2M2X (M = Pd, Pt; X = Al, Ga, Ge, Cd), and their structural relationship to the Laves phase Ca2Pt3Al1–xAgx

Optimization of Chemical Bonding through Defect Formation and Ordering─The Case of Mg7Pt4Ge4

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Synergistic Geometrical and Electronic Features in the Intermetallic Phases Ca₂AgM₂, Ca₂MgM₂, and Ca₂GaM₂ (M = Pd, Pt)

Optimization of Chemical Bonding through Defect Formation and Ordering─The Case of Mg₇Pt₄Ge₄