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

Abstract

We demonstrated crystal structures, magnetic, and optical properties of the B-site substituted double-perovskite Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Pr(Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> for the lightly Sb-substituted samples, indicating the valence mixing between Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> . The magnetic moments with the heavy Sb substitution are close to the valence of Pr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> . The magnitudes of bandgap energy for the two end-member samples were estimated from the optical measurements to be E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 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.