Crystals of Fe3R(BO3)4 (R
= Y, La, Nd) have been grown. Their structure and
properties
show close relations. The structures of these materials have been
established by single-crystal X-ray diffraction. They crystallize in the huntite,
CaMg3(CO3)4, structure
type,
trigonal system, space group R32 (No. 155), Z =
3, with unit-cell parameters (Å) a =
9.592(1),
9.578(1), and 9.563(2) and c = 7.597(7),
7.605(3), and 7.575(2), for R = La, Nd, and
Y0.5Bi0.5,
respectively. They contain RO6 trigonal prisms and
smaller FeO6 octahedra forming layers
and giving rise to Fe−R distances of ≃3.78 Å. RO6
polyhedra are interconnected within the
layers by corner sharing with triangular BO3 groups of two
types and FeO6 octahedra.
FeO6
octahedra form 1D helicoidal chains with relatively short Fe−Fe
distances, ≃3.18 Å. The
temperature dependence of the magnetic susceptibility from 350 to 1.8 K
for Fe3R(BO3)4
shows two maxima at about 260 and 35 K and, for R = Nd, another
maximum at 6 K. The
presence of magnetic order is attributed to magnetic Fe−Fe or
Fe−O−Fe interactions.
Infrared spectra in the range 4000−240 cm-1 show
the ν1, ν3, and ν4 IR-active
bands of the
B(1)O3
3- triangular groups as well as
ν2 of less symmetrical
B(2)O3
3-.