Pressure-Induced Phase Transition and Band Gap Decrease in Semiconducting β-Cu2V2O7.

Robin Turnbull,Akun Liang,Alfonso Muñoz,Fernando Rodríguez,Daniel Errandonea,Javier González-Platas,Zhangzhen He,Plácida Rodríguez-Hernández,David Santamaría-Pérez,Catalin Popescu

doi:10.1021/acs.inorgchem.1c03878

Abstract

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-Cu2V2O7, finding it undergoes a pressure-induced phase transition to γ-Cu2V2O7 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-Cu2V2O7 has previously been suggested as a promising photocatalyst for water splitting. Now, these new results suggest that β-Cu2V2O7 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%.

Highlights

We investigate the electronic structure via absorption spectroscopy and ab initio density functional theory calculations, in particular the optical band gap and sub-band d−d transitions associated with Cu2+ coordination complexes, finding the phase transition to be characterized by a 0.2 eV band gap decrease and a decrease in the average crystal field strength
The pressure-induced β → γ phase transition is unambiguously confirmed by single-crystal X-ray diffraction (XRD) and ab initio density functional theory calculations
The β → γ phase transition is associated with a volume collapse of approximately 7%, an increase in oxygen coordination of half of the Cu2+ coordination complexes, and a reorientation of 1-dimensional chains composed of edge sharing CuO6 units

Summary

Introduction

Copper(II) pyrovanadate, Cu2V2O7, has been highlighted as a favorable material for the photocatalytic splitting of water into hydrogen and oxygen due to its band gap energy.[1−3]. The present work investigates β-Cu2V2O7 under highpressure conditions at ambient temperature to explore the effect of pressure on the crystal and electronic structures. Cu2V2O7 has a number of interesting and useful properties; for example, β-Cu2V2O7 is a semiconducting antiferromagnetic material which has an (indirect) electronic band gap energy of ∼2 eV, which is optimal for absorbing energy within the solar range.[10] β-Cu2V2O7 exhibits interesting magnetic properties, due to its spin-1/2 honeycomb lattice of Cu2+ [3d9] ions, including quasi-1D antiferromagnetism.[11−13] β-.

Methods

Results

Conclusion