Pressure-Induced Phase Transition and Band Gap Decrease in Semiconducting β-Cu 2 V 2 O 7 .

The understanding of the interplay between crystal structure and electronic structure in semiconductor materials is of great importance due to their potential technological applications. Pressure is an ideal external control parameter to tune the crystal structures of semiconductor materials in order to investigate their emergent piezo-electrical and optical properties. Accordingly, we investigate here the high-pressure behavior of the semiconducting antiferromagnetic material β-Cu 2 V 2 O 7 , finding it undergoes a pressure-induced phase transition to γ-Cu 2 V 2 O 7 below 4000 atm. The pressure-induced structural and electronic evolutions are investigated by single-crystal X-ray diffraction, absorption spectroscopy and ab initio density functional theory calculations. β-Cu 2 V 2 O 7 has previously been suggested as a promising photocatalyst for water splitting. Now, these new results suggest that β-Cu 2 V 2 O 7 could also be of interest with regards to barocaloric effects, due to the low phase -transition pressure, in particular because it is a multiferroic material. Moreover, the phase transition involves an electronic band gap decrease of approximately 0.2 eV (from 1.93 to 1.75 eV) and a large structural volume collapse of approximately 7%.