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

Abstract

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.

La2Pd3Ge5 and Nd2Pd3Ge5 Compounds: Chemical Bonding and Physical Properties

“…The lowest negative charges are associated with Pd species: Pd2 (−0.62) is less negative than Pd1 (−0.71), which can be explained by the presence of Pd2–Pd2 contacts, with distances of ∼3.09 Å (see Table ), whereas Pd1 is coordinated by only La and Ge. The anionic behavior of Pd and other noble metals, e.g., Pt, Au, and Ag, has been recently reported also for other rare-earth binary and ternary intermetallics. ,,, All of the Ge charges are close to zero, in contrast to the formal (2 b )­Ge 2– and (0 b )­Ge 4– . The tiny negative charges indicate that interactions of Ge with the surrounding La and Pd should be interpreted as covalent rather than ionic.…”

“…The anionic behavior of Pd and other noble metals, e.g., Pt, Au, and Ag, has been recently reported also for other rare-earth binary and ternary intermetallics. 13,20,43,44 All of the Ge charges are close to zero, in contrast to the formal (2b)Ge 2− and (0b)Ge 4− . The tiny negative charges indicate that interactions of Ge with the surrounding La and Pd should be interpreted as covalent rather than ionic.…”

Unpredicted but It Exists: Trigonal Sc2Ru with a Significant Metal–Metal Charge Transfer

“…The collected outcomes, however, show some discrepancies with the available experimental data, 8 including our recent results on the constitutional properties of several Sc– T systems. 2 …”

“…This is the case of the alloys of the platinum group metals, which are of great practical interest in many fields, including catalysis and electronic and jewelry applications. From the structural chemical point of view, these compounds range from simple Laves and Hume–Rothery phases to complex approximants and quasicrystals. − The stability of an impressive number of new phases in numeorus binary systems of transition elements ( T ) was predicted by Curtarolo et al − To do that, a big structural data set of artificially generated compounds was created and their calculated formation energies at 0 K were compared in terms of the convex hull construction. The collected outcomes, however, show some discrepancies with the available experimental data, including our recent results on the constitutional properties of several Sc– T systems …”

“…The collected outcomes, however, show some discrepancies with the available experimental data, 8 including our recent results on the constitutional properties of several Sc−T systems. 2 Here, we focus on the Sc 2 T family of compounds: the stateof-the-art on their existence and crystal structure is summarized in Figure 1 (the experimental data were taken from Pearson's crystal data 8 and the high-throughput data from the AFLOW library 7 ). The Sc 2 T phases with T = Mn, Re, Fe, and Rh were neither obtained nor predicted, so that their existence should probably be excluded; indeed, the experimental and calculated results also completely agree for Pd, Pt, and Au.…”