Multiple dielectric relaxations and superior sonocatalysis of bismuth iron niobate pyrochlores via high-level Co-doping

Abstract Manipulating the structure of Bi-based pyrochlores can produce excellent physicochemical properties and novel phenomena due to lattice disorders and distortions. Herein, bismuth iron niobate pyrochlores via high-level Co-doping were successfully fabricated by a sol-gel auto-combustion method and the doping effects on their structural, magnetic, dielectric and sonocatalytic properties were systematically investigated. Rietveld refinements revealed substituting Fe sites with Co ions (at a ratio of 30%–80%) can maintain the pyrochlore phase and induce larger lattice distortion. New dielectric relaxation and outstanding magneto-dielectric effect with a maximal 4% coefficient were clearly observed in the heavily Co-doped sample at low temperatures, which correlate with structural disorder and magnetic state transitions. New types of dielectric anomalies that gradually change the relative permittivity but maintain the dielectric loss almost constant with increasing temperature or frequency and can be tuneable at different doping levels were first observed above room temperature. The activation of ultrasonic vibration-driven degradation in the specimens was evaluated by the catalytic oxidation of dye, and the Fe/Co-coexisting catalysts exhibited superior sonocatalytic activity with magnetic recyclability, opening up a new pathway of developing feature-rich pyrochlores in the catalytic field.