Electronic properties and high-pressure behavior of wolframite-type CoWO4

Abstract

In this work we characterize wolframite-type CoWO₄ under ambient conditions and under compression up to 10 GPa, with emphasis on its electronic structure. X-Ray diffraction and vibrational experiments, supported by ab initio calculations, show that CoWO₄ is stable under high-pressure conditions, as no structural changes are detected in the studied pressure range. Interesting findings come from optical absorption spectroscopy. On the one hand, CoWO₄ is confirmed to have one of the lowest band gaps among similar wolframites, around 2.25 eV. This makes CoWO₄ suitable for use in applications such as the photocatalysis of organic pollutants and water splitting. Additionally, a monotonic decrease of the band gap is found upon compression. This phenomenon is seldom observed in AWO₄ wolframites and is attributed to the open character of the d shell of Co²⁺. Our results are supported by theoretical ab initio simulations and are discussed with reference to other wolframites.