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 Ba₂Pr(Bi_1−xSb_x)O₆ (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 (C²}/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 μ_B for the lightly Sb-substituted samples, indicating the valence mixing between Pr³⁺ and Pr⁴⁺. The magnetic moments with the heavy Sb substitution are close to the valence of Pr³⁺. 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. [ABSTRACT FROM AUTHOR]