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.