Binary Intermetallics in the 70 atom % R Region of Two R–Pd Systems (R = Tb and Er): Hidden, Obscured, or Nonexistent?

Abstract

Although rare-earth-metal–transition-metal (R/T) phase diagrams have been explored extensively, our recent studies have uncovered new previously nonexistent binary intermetallics. These compounds belong to a narrow region between 70 and 71.4 atom % of the rare-earth metal but represent four different structure types. The binaries Tb 7 Pd 3 and Er 17 Pd 7 are compositionally approaching (less than 1 atom % difference) the previously reported R 2.16 Pd 0.89 (R = Tb and Er), and apparently form by peritectoid transformation, thus, being hard to detect by fast cooling. Tb 7 Pd 3 ( 1 ) crystallizes in the Th 7 Fe 3 structure type ( hP 20, P 6 3 mc , a = 9.8846(4) Å, c = 6.2316(3) Å, Z = 2) while Er 17 Pd 7 ( 2 ) belongs to the Pr 17 Co 7 type being its second reported representative ( cP 96, P 2 1 3, a = 13.365(2) Å, Z = 4). Er 17 Pd 7 ( 2 ) is overlapping with the cubic F -centered Er 2.11 Pd 0.89 ( 3b , Fd 3̅ m , a = 13.361(1) Å, Z = 32) with practically identical unit cell parameters but a significantly different structure. Electronic structure calculations confirm that heteroatomic R–T bonding strongly dominates in all structures; T–T bonding interactions are individually strong but do not play a significant role in the total bonding.

Overlooked Binary Compounds Uncovered in the Reinspection of the La–Au System: Synthesis, Crystal Structures, and Electronic Properties of La7Au3, La3Au2, and La3Au4

“…Rare earth metals (RE) that prefer the +III oxidation state form compounds with the Th 7 Fe 3 structure when combined with transition elements of groups 8–10. 54 − 66 In addition, binary compounds Sc 7 P 3 and La 7 Ge 3 , containing main-group elements, were reported to crystallize in this type. 67 , 68 From these examples, it is clear that the existence field of the Th 7 Fe 3 structure extends over a wide region of valence electron counts.…”

“…Among the gold-containing phases, the Th 7 Fe 3 type is adopted by M 7 Au 3 with M = Sr, Eu, and Yb, − i.e., the metals that have a tendency to adopt the +II oxidation state. Rare earth metals (RE) that prefer the +III oxidation state form compounds with the Th 7 Fe 3 structure when combined with transition elements of groups 8–10. − In addition, binary compounds Sc 7 P 3 and La 7 Ge 3 , containing main-group elements, were reported to crystallize in this type. , From these examples, it is clear that the existence field of the Th 7 Fe 3 structure extends over a wide region of valence electron counts. However, it is not clear at the moment if other RE 7 Au 3 compounds exist and whether any of them are thermodynamically stable.…”

Spotlight on Alkali Metals: The Structural Chemistry of Alkali Metal Thallides

“…16. Thallides very rich in alkali metal are only reported for lithium and sodium and in general, a high content of alkali metal increases the complexity of the compounds [70,71]. Lithium compounds crystallize in known intermetallic structure types, interestingly they are isotypic to lithium tetrelides, The corresponding range of distances to the adjacent atoms as well as the Wyckoff letters are given in Table 16.…”