Electronic structure of yttrium-doped zinc ferrite – Insights from experiment and theory

In this work we have studied the effects of yttrium-doping to electronic structure of zinc ferrite. Our present study encompasses combination of experimental and computational procedures, with the aim of understanding how important and typical properties of title nanomaterial could be modified with frequently employed rare-earth element. Co-precipitation approach was used for the synthesis of zinc ferrite and its yttrium-doped derivatives, followed by characterization and experimental measurements of activation energies. Structures of zinc ferrite and yttrium-doped zinc ferrite were then subjected to detailed computational investigations in the framework of density functional theory (DFT). It has been shown that yttrium doping at the sites of zinc atoms produces significantly higher increase of unit cell parameter. DFT calculations encompassed geometrical optimizations, thanks to which information about structural properties have been acquired. Details about band structure have been obtained by DFT + U calculations and the calculated band gaps were related with the experimentally obtained information on activation energies. It has been shown by calculations that band gap of pristine ZFO is 0.922 eV, and that it can be manipulated by replacing iron ions with yttrium. The band gap values decrease to 0.899 eV when two yttrium ions are introduced to sites of iron ions, while the third Y increases band gap to the value of 1.027 eV. On the other side, replacing of zinc ions with yttrium leads to the formation of n-type semiconductor. Detailed insights into the effects of yttrium were also discussed through investigation of density of states. The results indicate different effects of yttrium doping, depending on whether iron or zinc atoms are replaced. It was particularly interesting to identify the formation of intermediate bands in cases when mixed spinel phase zinc ferrite was doped with yttrium.