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

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 AWO(4) 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.