Magnetic States and Bandgaps of B-Site Substituted Double-Perovskite Ba2Pr(Bi, Sb)O6

We demonstrated crystal structures, magnetic, and optical properties of the B-site substituted double-perovskite Ba
₂
Pr(Bi
_1−x
Sb
_x
) O
₆
(
$x=0$
, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, and 1.0). The single-phase polycrystalline samples with the light Sb substitution are formed in a monoclinic structure (
$C^{2}/m$
). The heavily Sb-substituted samples crystallize in the rhombohedral system accompanied by B-site disorder. Magnetization measurements show that the effective magnetic moments are located around
$3.2~\mu _{B}$
for the lightly Sb-substituted samples, indicating the valence mixing between Pr
³⁺
and Pr
⁴⁺
. The magnetic moments with the heavy Sb substitution are close to the valence of Pr
³⁺
. The magnitudes of bandgap energy for the two end-member samples were estimated from the optical measurements to be
$E_{g} = 0.977$
eV at
$x=0$
and 2.395 eV at
$x=1.0$
. The effect of the bandgap opening due to Sb substitution is examined by using the density functional theory. The lightly and heavily Sb-doped compounds show typical absorption edges in indirect and direct semiconductors, respectively. These findings are qualitatively consistent with the calculated results.