Microstructural changes caused by Ba and Pr doping in nanosized Bi2Ce2O7 leading to interesting optical, magnetic, and catalytic properties

Abstract

Defect fluorite structured Bi₂Ce₂O₇ having equal concentrations of bismuth and cerium presents an exciting scenario in which one can tilt its redox character by appropriate doping schemes. In the current work, the correlation of microstructural changes brought about by the inclusion of aliovalent/isovalent ion doping (Ba²⁺, Pr³⁺/Pr⁴⁺) with the optical, magnetic, and catalytic properties of Bi₂Ce₂O₇ is attempted by synthesizing samples following a simple wet-chemical method. The fluorite structure was retained for the doped samples. The observed lattice contraction in both the doped systems was rationalized from the ionic radii of cations and oxygen vacancies. The doped samples had crystallites with an average size of 5 nm. A change in bond length and atomic geometry, brought about by the Pr-doping, resulted in the reduction in the intensity of the oxygen vacancy band in the Raman spectrum, whereas the Ba-doping enhanced the intensity of the oxygen vacancy band. Quantification of oxygen vacancies showed that the Ba-doped sample had more defects than the Pr-doped sample. The optical bandgap showed a reduction in both cases. While Pr⁴⁺ coexisted with Ce³⁺ and Ce⁴⁺ in the Pr-doped sample, cerium existed solely as Ce⁴⁺ in the Ba-doped sample. The Ce³⁺ emission intensity was enhanced in the Pr-doped sample, whereas oxygen vacancy blue-green emission dominated the Ba-doped sample. From magnetic field dependent measurements, the coexistence of ferro- and antiferromagnetic domains was observed in the Pr-doped sample. The rate of reduction of 4-nitrophenol, 4-aminophenol, and 2,4-dinitrophenol to their amine analogs in the presence of the barium doped sample was way higher than that with the Pr-doped sample. The higher catalytic capability of the barium doped sample was correlated with its highest oxygen vacancy concentration.