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

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 TbPd and ErPd are compositionally approaching (less than 1 atom % difference) the previously reported RPd (R = Tb and Er), and apparently form by peritectoid transformation, thus, being hard to detect by fast cooling. TbPd () crystallizes in the ThFe structure type (20, 6, = 9.8846(4) Å, = 6.2316(3) Å, = 2) while ErPd () belongs to the PrCo type being its second reported representative (96, 23, = 13.365(2) Å, = 4). ErPd () is overlapping with the cubic -centered ErPd (, 3̅, = 13.361(1) Å, = 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.