Structural, physical and photocatalytic properties of mixed-valence double-perovskite Ba$_{2}$Pr(Bi,Sb)O$_{6}$ semiconductor synthesized by citrate pyrolysis technique.

We demonstrated crystal structures, magnetic, optical, and photocatalytic properties of the B-site substituted double perovskite Ba$_{2}$Pr(Bi$_{1-x}$Sb$_{x}$)O$_{6}$ ($x$=0, 0.1, 0.2, 0.5 and 1.0) synthesized by the citrate pyrolysis method. The single-phase polycrystalline samples with the light Sb substitution crystallized in a monoclinic structure ($I2/m$). Magnetization measurements on all the samples showed that the effective magnetic moments are located around 3 $\mu_{B}$ , indicating the valence mixing states between Pr$^{3+}$ and Pr$^{4+}$.The magnitudes of band gap energy for the two end member samples were estimated from the optical measurements to be $E_{g}$ =1.06 eV at $x$=0 and 2.71 eV at $x$=1.0. The Ba$_{2}$Pr(Bi$_{1-x}$Sb$_{x}$)O$_{6}$ ($x$=0, and 0.1) powders obtained by the present technique exhibited enhanced photocatalytic activities when compared to the same compounds prepared by the conventional solid state method. Our findings suggest that the higher photocatalytic activities strongly depend on powder preparation method as well as the band gaps and charge separation.