First-principles Study Of The Electronic, Mechanical And Optical Properties Of BiVO₄

Bismuth vanadate(BiVO4)is a promising candidate compound for photocatalytic hydrogen production and photocatalytic degradation of organics.It has been found that there are four phases of BiVO4:tetragonal zirconium silicate phase(T-1),tetragonal scheelite phase(T-2),orthorhombic pucherite phase(O)and monoclinic β-fergusonite phase(M),and they exhibit significant band structure and optical properties.In this paper,the first-principle calculations of its structural stability,band structure and optical properties were performed.The results show that the stable phase is pressure-dependent and the most stable phases are the T-1 and T-2 phases under 0 GPa and 2 GPa,respectively,while the most stable one is M phase under 4GPa,6GPa and 8GPa.BiVO4 in any case are indirect band gap semiconductors,and its band gaps decreases with increasing pressure.What is more,the external pressure can improve the hybridization of O 2p,V 3d and Bi 6s orbitals,and the band edges shift to lower energies.We studied the dielectric function,optical refractive index,absorption coefficient and reflectivity of the material.We found that the optical curves occurred red-shifted with increasing pressure in the low-energy region,and the T-1 phase and M phase has almost the same optical characteristics although they have different lattice structures.That is to say,the optical properties can be adjusted to some extent by changing the pressure,which is beneficial for optical applications.Furthermore,we used first-principles calculations to investigate the effect of oxygen vacancy of the monoclinic BiVO4 on the structural,electronic,elastic,and optical properties.The results show that oxygen vacancy of BiVO4(Vo-BiVO4)can stably exist,and the transition of band gap from indirect to direct.Basically,oxygen vacancy can improve the hybridization of 02p,V3d and Bi6s orbitals and the band edges shift to lower energies.The result is similar to the above,the curves of dielectric functions,refractive indices,absorption coefficients,reflectivities,loss functions,and electrical conductivity occurred red-shifted at low energies.Therefore,the introduction of oxygen vacancy can control the optical properties of BiVO4 to a certain degree,which is conducive to optical applications.Finally,in this paper,we also calculated the elastic constants,structural stability,electronic properties and optical properties of ideal BiVO4 and Vo-BiVO4 under quivalent hydrostatic pressure and z-axial pressure.It is found that although the elastic constants of ideal BiVO4 and Vo-BiVO4 have changed due to external quivalent hydrostatic pressure and z-axial pressure,its structural stability is not affected and BiVO4 always maintains indirect band gap semiconductors under pressure.The hybridization of 02p,V3d and Bi6s orbitals improved in the ideal BiVO4,while the hybridization of the 02p,V3d and Bi6p orbitals improved in Vo-BiVO4 with increasing pressure.Under external pressure,all of the band edges move to lower energies,resulting in a noticeable decrease in band gap and might improved photocatalytic performance.The light absorptions of the ideal BiVO4 and Vo-BiVO4 increase with increasing z-axial pressure,thus contributing to the increase of visible light absorption of the ideal BiVO4 and Vo-BiVO4.