Crystal chemistry and chemical order in ternary quasicrystals and approximants

Gómez, Cesar Pay; Tsai, A.‐P.

doi:10.1016/j.crhy.2013.10.007

Cited by 10 publications

(7 citation statements)

References 35 publications

(43 reference statements)

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“…The atomic ordering follows an empirical rule for isostructural approximants. This rule states that the middle edge positions of the RTH shell (M3) are occupied by pure p-block elements (i.e., Al, Ga, In, Sn, Ge, or Si), while the vertex positions of the shell (M5) are predominantly occupied by d-block elements (i.e., Zn, Cd, Ag, or Au) . In addition, positions M2, M6, and M7 are commonly occupied by mixtures of Au and Ga/Al in both Yb–Ga–Au and Yb–Al–Au 1/1 APs.…”

Section: Resultsmentioning

confidence: 99%

“…However, the selective occupation of various constituent elements has been observed in RTH clusters. As an example, the vertices of the triacontahedron shell are preferentially occupied by Mg atoms when the Cd sites in both the Yb–Mg–Cd 1/1 AP and the iQCs are occupied by Mg. , The presence of ordered and mixed sites thus indicates that both the electronic structure and the extent of partial chemical disorder are important factors in the stabilization mechanism.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and Atomic Structure of the Yb–Ga–Au 1/1 Quasicrystal Approximant

Yamada

Kurihara

Prots³

et al. 2019

Inorg. Chem.

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The Yb–Ga–Au 1/1 quasicrystal approximant (AP) composition ranges from Yb14.0Ga20.6Au65.4 to Yb14.8Ga46.3Au38.9, and single crystals of the 1/1 AP having the composition Yb13.8Ga26.1Au60.1 were obtained by the self-flux technique. X-ray structural analysis demonstrated that the atomic structure [space group Im ; a = 14.6889(9) Å] can be described by the body-centered packing of Tsai-type rhombic triacontahedron (RTH) clusters. The positional disorder in these clusters, interpreted as the average of an orientationally disordered tetrahedron and triangle, results in positional disorder in the outer shells. The elemental distributions and positions of mixtures of Au and Ga atoms in the RTH clusters correspond to those in the isostructural Yb15Al36Au49 1/1 AP.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Synthesis and Atomic Structure of the Yb–Ga–Au 1/1 Quasicrystal Approximant

Yamada

Kurihara

Prots³

et al. 2019

Inorg. Chem.

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“…Statistical data elaboration based on symmetry properties, such as space group, Pearson symbol, lattice parameters, and standardized representations may help to some extent, but it is also known that among intermetallics, frequently, structural relations exist between chemically different systems with different numbers of atoms in the unit cell, different sets of Wyckoff sequences, and different space groups. The Hume-Rothery (HR) phases and ACs offer numerous examples of this. − …”

Section: Resultsmentioning

confidence: 99%

“…From the above discussion, it becomes clear that starting from the central atom, substitutions are initially more favored (from Pd1 to Sc8), then the formation of defects of both types (from Pd2 to Sc9) competes, whereby the fourth shell is the preferred one for disordering phenomena. This observation is consistent with the structural trends observed in Tsai-type clusters: the atomic positions of the inner shell are less affected by chemical disorder but instead the RTH sites are susceptible to mixed occupancies …”

Section: Resultsmentioning

confidence: 99%

New Quasicrystal Approximant in the Sc–Pd System: From Topological Data Mining to the Bench

et al. 2020

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Intermetallics contribute significantly to our current demand for high-performance functional materials. However, understanding their chemistry is still an open and debated topic, especially for complex compounds such as approximants and quasicrystals. In this work, targeted topological data mining succeeded in (i) selecting all known Mackay-type approximants, (ii) uncovering the most important geometrical and chemical factors involved in their formation, and (iii) guiding the experimental work to obtain a new binary Sc–Pd 1/1 approximant for icosahedral quasicrystals containing the desired cluster. Single-crystal X-ray diffraction data analysis supplemented by electron density reconstruction using the maximum entropy method, showed fine structural peculiarities, that is, smeared electron densities in correspondence to some crystallographic sites. These characteristics have been studied through a comprehensive density functional theory modeling based on the combination of point defects such as vacancies and substitutions. It was confirmed that the structural disorder occurs in the shell enveloping the classical Mackay cluster, so that the real structure can be viewed as an assemblage of slightly different, locally ordered, four shell nanoclusters. Results obtained here open up broader perspectives for machine learning with the aim of designing novel materials in the fruitful field of quasicrystals and their approximants. This might become an alternative and/or complementary way to the electronic pseudogap tuning, often used before explorative synthesis.

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“…The predominance of i-QCs over the other QC classes seemingly correlates with the predominance of the 12-atom pseudoicosahedral local environments within many complex intermetallic compounds, and the complexity of i-QCs, especially among multinary systems, suggests the need for more structural research . Crystalline phases that are nearby in composition to corresponding QCs are coined “crystalline approximants” (CAs) because they are proposed to approximate the structures of related i-QCs, and are good starting points for study …”

Section: Introductionmentioning

confidence: 99%

From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation

Pham¹,

Meng

Lynn

et al. 2018

J. Am. Chem. Soc.

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The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAuAl to its cubic 2/1 crystalline approximant (CA) CaAuAl (CaAuAl, Pa3̅ (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at ∼570 °C and complete by ∼650 °C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [AuAl□] and an icosahedral shell of only Al [Al□]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au-Al nearest neighbor contacts over homoatomic Al-Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. According to electronic structure calculations, a cubic 1/1 CA, "CaAuAl" (CaAuAl) is proposed.

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Crystal chemistry and chemical order in ternary quasicrystals and approximants

Cited by 10 publications

References 35 publications

Synthesis and Atomic Structure of the Yb–Ga–Au 1/1 Quasicrystal Approximant

Synthesis and Atomic Structure of the Yb–Ga–Au 1/1 Quasicrystal Approximant

New Quasicrystal Approximant in the Sc–Pd System: From Topological Data Mining to the Bench

From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation

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