Structural modulation enables magneto-dielectric effect and enhanced photoactivity in ferroelectric bismuth iron niobate pyrochlore

Abstract

Bismuth-based pyrochlore oxides in which the structure tolerates significantly lower site misplacement and markedly higher vacancy concentrations exhibit unique physicochemical properties; therefore, manipulation of such a crystal structure by chemical substitution may give rise to intriguing phenomena and extraordinary properties. Herein, we have systematically investigated the effects of the Co substitution on the structural, magnetic, magneto-dielectric and optoelectronic characteristics of ternary bismuth iron niobate pyrochlore oxide with the highest recorded Fe content. Structural modulation induced by the Co dopant was clearly observed by Rietveld refinements and Raman spectra, which are attributed to the displacive disorder nature of the pyrochlore structure and lattice distortions induced by the substitution of Fe sites with Co ions. A dielectric anomaly exhibits a distinct peak temperature shift and intensity increasing under a magnetic field of 1 T, which may be explained in terms of the magnetic state transition and magnetic interactions or fluctuations, and the obvious magneto-dielectric (MD) effect with a maximal MD coefficient of ∼4% at ∼1 MHz was firstly found in ferroelectric Bi pyrochlores. Remarkably, the Fe/Co-coexisted nanoparticles showed an anomalous light absorption and exhibited an enhanced visible-light-responsive photocatalytic performance by means of the dye decomposition and the photoelectrochemical technique. The findings indicated structural modulation using element substitution can realize excellent physicochemical behaviours and novel phenomena and shed new light on controlling the atomic structure and functional properties in isostructural pyrochlore oxides.