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

[Image: see text] 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 (hP20, P6(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 (cP96, P2(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, Fd3̅m, 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.