Putting ScTGa<sub>5</sub>(T = Fe, Co, Ni) on the Map: How Electron Counts and Chemical Pressure Shape the Stability Range of the HoCoGa<sub>5</sub>Type

Engelkemier, Joshua; Green, Lance M.; McDougald, Roy N.; McCandless, Gregory T.; Chan, Julia Y.; Fredrickson, Daniel C.

doi:10.1021/acs.cgd.6b00855

Cited by 8 publications

(8 citation statements)

References 79 publications

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“…Since the 4f orbitals of the lanthanide atoms are highly contracted around their cores, they are not expected to participate significantly in interatomic interactions. As such, the lanthanides bring only their 6s, 5d, and 6p orbitals to the bonding, and they may be considered transition metals within the context of the 18- n rule, as was concluded previously for HoCoGa 5 -type compounds . Each RE Al 3 phase has 12 valence electrons per RE atom, which gives n = 6 for the number of nearest-neighbor RE - RE isolobal bonds needed around each RE atom.…”

Section: Resultsmentioning

confidence: 88%

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl₃ (RE = Sc, Y, Lanthanides) Series

2023

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Atomic packing and electronic structure are key factors underlying the crystal structures adopted by solid-state compounds. In cases where these factors conflict, structural complexity often arises. Such is born in the series of REAl 3 (RE = Sc, Y, lanthanides), which adopt structures with varied stacking patterns of face-centered cubic close packed (FCC, AuCu 3 type) and hexagonal close packed (HCP, Ni 3 Sn type) layers. The percentage of the hexagonal stacking in the structures is correlated with the size of the rare earth atom, but the mechanism by which changes in atomic size drive these large-scale shifts is unclear. In this Article, we reveal this mechanism through DFT-Chemical Pressure (CP) and reversed approximation Molecular Orbital (raMO) analyses. CP analysis illustrates that the Ni 3 Sn structure type is preferable from the viewpoint of atomic packing as it offers relief to packing issues in the AuCu 3 type by consolidating Al octahedra into columns, which shortens Al−Al contacts while simultaneously expanding the RE atom's coordination environment. On the other hand, the AuCu 3 type offers more electronic stability with an 18-n closed-shell configuration that is not available in the Ni 3 Sn type (due to electron transfer from the RE d z 2 atomic orbitals into Al-based states). Based on these results, we then turn to a schematic analysis of how the energetic contributions from atomic packing and the electronic structure vary as a function of the ratio of FCC and HCP stacking configurations within the structure and the RE atomic radius. The minima on the atomic packing and electronic surfaces are non-overlapping, creating frustration. However, when their contributions are added, new minima can emerge from their combination for specific RE radii representing intergrowth structures in the REAl 3 series. Based on this picture, we propose the concept of emergent transitions, within the framework of the Frustrated and Allowed Structural Transitions principle, for tracing the connection between competing energetic factors and complexity in intermetallic structures.

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Section: Resultsmentioning

confidence: 88%

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl₃ (RE = Sc, Y, Lanthanides) Series

2023

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“…Of note is the ease with which these two structural modules fit together: 4-fold-symmetric CaAl 4 -like polyhedra match perfectly into the concave holes of the fluorite structure fragment. Such compatibility between the BaAl 4 and fluorite types is well-known from their lamellar intergrowth in BaMg 4 Si 3 - and Ce 2 NiGa 10 -type compounds, among others. − …”

Section: Resultsmentioning

confidence: 92%

Intermetallic Reactivity: Ca₃Cu_7.8Al_26.2 and the Role of Electronegativity in the Stabilization of Modular Structures

2020

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The structural chemistry of intermetallic phases is generally viewed in terms of what crystal structure will be most stable for a given combination of metallic atoms. Yet, individual atoms do not always make the best reference points. As the number of elements involved in compounds increases, their structures can often appear to be assembled from structural motifs derived from simpler compounds nearby in the phase diagram rather than fundamentally new arrangements of atoms. In this Article, we explore the notion that complex multinary phases can be viewed productively in terms of motif-preserving reactions between binary compounds, as opposed to direct reactions of the component elements. We present the targeted synthesis and structure solution of Ca3Cu7.8Al26.2, an intermetallic phase whose placement in the phase diagram is suggestive of a reaction between CaAl4 and CuAl2. Single-crystal X-ray diffraction analysis reveals that this compound crystallizes in the Y3TaNi6+x Al26 (or stuffed BaHg11) structure type and is constructed from three modules: Ca@(Cu/Al)16 polyhedra derived from the BaAl4 type, Cu@Al8 cubes, and Al13 cuboctahedra. To help understand this arrangement, we identify forces driving the reactivity of one of the supposed starting materials, CaAl4, through visualization of its atomic charge distribution and chemical pressure (CP) scheme, which suggest that the Al sites closest to the Ca atoms should show a high affinity for substitution by Cu atoms. Such a process on its own, however, would lead to overly long Ca–Cu distances and electron deficiency. When Cu is made available to CaAl4 in the Ca–Cu–Al ternary system, its incorporation in the Ca coordination environments instead nucleates domains of a fluorite-like CuAl2 phase, which act as nodes in the primitive cubic framework of CaAl4- and fluorite-like units. The cubic holes created by this framework are occupied by Al13 face-centered-cubic fragments that donate electrons while also resolving negative CPs in the Ca environments. This structural chemistry illustrates how new elements added to a binary compound at sites with conflicting electronic and atomic size preferences can serve as anchor points for the growth of domains of different bonding types, a notion that can be applied as a more general design strategy for new intermetallic intergrowth structures.

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“…This method is based on the recognition that non-optimal interatomic distances are detectable in the local pressures that surround the atoms of a solid-state lattice, as constructed from the output of DFT calculations. In the study of a variety of intermetallic phases, CP analysis has provided explanations for diverse structural phenomena, such as the insertion of interfaces into simple structures [19,20,24,25], the adoption of local icosahedral symmetry in quasicrystal approximants [26][27][28], the emergence in incommensurability [29][30][31][32][33][34], the stabilizing effects of various kinds of single point substitutions [23][24][25]35,36], and the formation of intergrowth structures [27,35,[37][38][39]. The CP maps generated in the process can also be used to analyze the forces involved in chemical bonding and molecular structure [40][41][42][43].…”

Section: Introductionmentioning

confidence: 99%

Tutorial on Chemical Pressure Analysis: How Atomic Packing Drives Laves/Zintl Intergrowth in K3Au5Tl

Buskirk

Cheng

et al. 2021

Crystals

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The tight atomic packing generally exhibited by alloys and intermetallics can create the impression of their being composed of hard spheres arranged to maximize their density. As such, the atomic size factor has historically been central to explanations of the structural chemistry of these systems. However, the role atomic size plays structurally has traditionally been inferred from empirical considerations. The recently developed DFT-Chemical Pressure (CP) analysis has opened a path to investigating these effects with theory. In this article, we provide a step-by-step tutorial on the DFT-CP method for non-specialists, along with advances in the approach that broaden its applicability. A new version of the CP software package is introduced, which features an interactive system that guides the user in preparing the necessary electronic structure data and generating the CP scheme, with the results being readily visualized with a web browser (and easily incorporated into websites). For demonstration purposes, we investigate the origins of the crystal structure of K3Au5Tl, which represents an intergrowth of Laves and Zintl phase domains. Here, CP analysis reveals that the intergrowth is supported by complementary CP features of NaTl-type KTl and MgCu2-type KAu2 phases. In this way, K3Au5Tl exemplifies how CP effects can drive the merging for geometrical motifs derived from different families of intermetallics through a mechanism referred to as epitaxial stabilization.

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Putting ScTGa₅(T = Fe, Co, Ni) on the Map: How Electron Counts and Chemical Pressure Shape the Stability Range of the HoCoGa₅Type

Cited by 8 publications

References 79 publications

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl₃ (RE = Sc, Y, Lanthanides) Series

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl₃ (RE = Sc, Y, Lanthanides) Series

Intermetallic Reactivity: Ca₃Cu_7.8Al_26.2 and the Role of Electronegativity in the Stabilization of Modular Structures

Tutorial on Chemical Pressure Analysis: How Atomic Packing Drives Laves/Zintl Intergrowth in K3Au5Tl

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Putting ScTGa5(T = Fe, Co, Ni) on the Map: How Electron Counts and Chemical Pressure Shape the Stability Range of the HoCoGa5Type

Cited by 8 publications

References 79 publications

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl3 (RE = Sc, Y, Lanthanides) Series

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl3 (RE = Sc, Y, Lanthanides) Series

Intermetallic Reactivity: Ca3Cu7.8Al26.2 and the Role of Electronegativity in the Stabilization of Modular Structures

Tutorial on Chemical Pressure Analysis: How Atomic Packing Drives Laves/Zintl Intergrowth in K3Au5Tl

Contact Info

Product

Resources

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Putting ScTGa₅(T = Fe, Co, Ni) on the Map: How Electron Counts and Chemical Pressure Shape the Stability Range of the HoCoGa₅Type

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl₃ (RE = Sc, Y, Lanthanides) Series

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl₃ (RE = Sc, Y, Lanthanides) Series

Intermetallic Reactivity: Ca₃Cu_7.8Al_26.2 and the Role of Electronegativity in the Stabilization of Modular Structures