From simple to complex crystal chemistry in the RE–Au–Tt systems (RE = La, Ce, Pr, Nd; Tt = Ge, Pb)

Abstract

Polar intermetallics are an intriguing class of compounds with complex relationships between composition and structure that are not fully understood. This work reports a systematic study of the underexplored ternary composition space RE−Au−Tt (RE = La, Ce, Pr, Nd; Tt = Ge, Pb) to expand our knowledge of the intriguing chemistry and diversity achievable with these metallic constituents. These composition spaces are particularly interesting because of the potential to find Au-bearing, highly polar intermetallic compounds. The elements were first reacted through arc welding under an inert atmosphere, followed by annealing at 850 °C. X-ray diffraction of the products identified seven unreported compounds ranging from the simple NaTl-type compounds La 1.5 Au 2 Pb 0.5 and Nd 2−x Au 2 Pb x to the more structurally complex La 5 AuPb 3 in the Hf 5 CuSn 3 -type structure and Pu 3 Pd 4 -type RE 3 Au 3 Ge (RE = La, Ce, Pr, Nd). Firstprinciples electronic structure calculations investigate the combination of Fermi surface−Brillouin zone interactions, electrostatic interactions, and delocalized metallic bonding that contributes to the formation of these phases. These calculations show that a mixture of electrostatic and metallic bonding plays a dominant role in these phases. The RE−Au−Tt composition space remains full of potential for discovering materials with relevant magnetic and quantum properties, provided the crystal chemistry can be comprehended.

Electronic and structural properties of Y6Pt13X4, site occupancy variants of the Ba6Na16N subnitride (X = Al, Ga)

“…81,89 The described bonding characteristics, found for alkali metal suboxides and subnitrides, were recently paralleled with novel intermetallics. [90][91][92][93][94][95] The polar intermetallic phases show lower valence electron concentration relative to those of the Zintl phases, 96,97 but close to those of the Hume-Rothery phases. 98 Due to the lack in straightforward valence electron rules for polar intermetallics, the exploration of this category of compounds is desirable to expand the understanding of chemical principles that govern their stabilities and chemical bonding.…”

“…83 Concerning rare earth intermetallics with noble metals, some already available phases in related systems ( e.g. , a polar intermetallic La 3 Au 3 Ge 93 which crystallizes with the Pu 5 Pd 4 -type and exhibits the modified Au/Ge network which surrounds the [AuLa 6 ] octahedra, etc .) are excellent indications of novel possibilities for developments of new polar metallic phases, with further perspectives of exploring new bonding interactions, modulated by composition.…”

From Laves Phases to Quasicrystal Approximants in the Na–Au–Cd System

“…The exploratory synthesis of metal-rich, inorganic solids has revealed a collection of unprecedented crystal structures, distinct bonding motifs, and unique electronic features . Ternary systems containing metal constituents featuring exceedingly different electronegativities have been particularly bountiful, yielding a wide variety of exciting intermetallic compounds. − These compounds have attracted great interest because of their fascinating physical properties such as superconductivity, − topology, − magnetism, − and catalytic properties. − They also contain unique structural traits like complex networks, , clusters, quasicrystals, and their approximants . Nevertheless, the specific chemistry dictating crystal structure formation and the ensuing properties has remained ambiguous.…”

Twists and Puckers: Tuning Crystal Chemistry in the La(AuxGe1–x)2 Compositional Series

“…18,19 In this space, Au-containing polar intermetallics are of particular interest because Au's high electron affinity enables unique crystal chemistries not seen in analogous systems. 20,21 RE-Au-Tt (RE = rare earth, Tt = group IV metal/metalloid) compounds highlight this competition through their structural diversity, as evidenced by the 34 unique structure types reported for these compositions in the ICSD. 22 Thus, these systems are an ideal venue to explore subtle changes in structure−composition relationships.…”

“…In this work, we investigate the subtle interplay between composition and structure preference by examining the La­(Au x Ge 1– x ) 2 compositional series. This family of polar intermetallics exists in a poorly understood middle ground between the more classical Hume–Rothery (e – /atom ≤2) and Zintl (e – /atom ≥4) regimes, with valence counts between 1.2 and 4.0 electrons per atom. , − Unlike their counterparts, these compounds do not follow simple electron counting rules and often produce crystal structures that hang in the balance between chemical bonding, electrostatic interactions, and atomic size requirements. , In this space, Au-containing polar intermetallics are of particular interest because Au’s high electron affinity enables unique crystal chemistries not seen in analogous systems. , RE- Au- Tt ( RE = rare earth, Tt = group IV metal/metalloid) compounds highlight this competition through their structural diversity, as evidenced by the 34 unique structure types reported for these compositions in the ICSD . Thus, these systems are an ideal venue to explore subtle changes in structure–composition relationships.…”