Polaron formation, native defects, and electronic conduction in metal tungstates

Abstract

Iron tungstate (FeWO${}_4$) and manganese tungstate (MnWO${}_4$) belong to a family of wolframite-type materials that has applications in various areas, including supercapacitors, batteries, and multiferroics. A detailed understanding of bulk properties and defect physics in these transition-metal tungstates has been lacking, however, impeding possible improvement of their functional properties. Here, we report a first-principles study of FeWO${}_4$ and MnWO${}_4$ using screened hybrid density-functional calculations. We find that in both compounds the electronic structure near the band edges are predominantly the highly localized transition-metal $d$ states, which allows for the formation of both hole polarons at the Fe (Mn) sites and electron polarons at the W sites. The dominant native point defects in FeWO${}_4$ (MnWO${}_4$) under realistic synthesis conditions are, however, the hole polarons at the Fe (Mn) sites and negatively charged Fe (Mn) vacancies. The presence of low-energy and highly mobile polarons provides explanation for the good p-type conductivity observed in experiments and the ability of the materials to store energy via a pseudocapacitive mechanism.

arXiv comment8 pages, 5 figures

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Cited by in corpus (3)

• Defect physics in complex energy materials
• First-principles theory of doping in layered oxide electrode materials
• The effect of pressure in the crystal and magnetic structure of FeWO4