BiOF_(1-x)Cl_(x)固溶体的光电性质优化及第一性原理研究

Optimization of Optoelectronic Properties and First-principles Study of BiOF_(1-x)Cl_(x)Solid Solutions

BiOF和BiOCl都是紫外光响应降解有机污染物的高效典型光催化剂,但其光吸收带边分别为4.00eV和3.77eV,只能吸收部分紫外光进行催化反应,因此光催化效率受到限制。受到半导体能带弯曲现象的启发,本文采用团簇展开方法(cluster expansion,CE)并结合第一性原理计算,搜索了BiOF_(1-x)Cl_(x)有序及无序固溶体的晶体结构,计算了这些固溶体的热力学性质和光电性质。计算结果表明,在BiOF_(1-x)Cl_(x)的有序固溶体中,Cl-更倾向于优先取代同一层的F-;在BiOF_(1-x)Cl_(x)的无序固溶体中,Cl-随机取代F-。以BiOF_(0.50)Cl_(0.50)为例,无序固溶体的形成焓ΔH比有序固溶体高60meV·(f.u.)-1。BiOF_(1-x)Cl_(x)(0<x<1)的有序及无序固溶体多为间接带隙半导体,且带隙大小呈现不同程度的能带弯曲。低温时,BiOF_(1-x)Cl_(x)固溶体多为有序固溶体,x=0.17时,能带弯曲程度最大。高温时,无序BiOF_(1-x)Cl_(x)固溶体更容易形成,且x=0.60时,能带弯曲程度最大,吸收带边红移至3.59eV,带边吸收强度提升了2个数量级。基于本工作的计算结果,我们预测BiOF和BiOCl形成的固溶体在紫外区的光吸收范围和吸光效率,会得到进一步的提升。

Both BiOF and BiOCl were highly efficient photocatalysts for organic pollutants degradation under ultra-violet radiation.However,the photocatalytic efficiencies were limited by their light harvest beyond 4.00eV and 3.77eV.Inspired by the band gap bowing effect of semiconductor alloys,the ordered and disordered crystal structures of BiOF_(1-x)Cl_(x) solid solutions were searched and calculated by the cluster expansion method(CE)combined with the first-principle calculations.The thermodynamic and electronic,and photoelectronic properties of the obtained alloy structures were further studied.Cl-prefered to replace F-in the same layer to stabilize the ordered BiOF_(1-x)Cl_(x) solid solutions according to the calculation.In contrast,Cl-randomly replaced F-in disordered BiOF_(1-x)Cl_(x) solid solutions.The formation enthalpyΔH of the disordered BiOF_(0.50)Cl_(0.50) solid solution was 60meV/f.u.higher than that of the ordered phase.The obtained band structure of the ordered and disordered BiOF_(1-x)Cl_(x)(0<x<1)were mostly indirect,and the widths of the band gaps exhibited bowing effecpt to different extents.At low temperature,the BiOF_(1-x)Cl_(x) solid solution was flavored,when x=0.17 the band gap bowing was dramatic.Whereas,at high temperature,the disordered BiOF_(1-x)Cl_(x) solid solution was more easily synthesized,and the band gap bowing was most dramatic when x=0.60.The absorption band edge of the BiOF0.40Cl0.60 was predicted to red-shifted to 3.59eV and the absorption intensity was enhanced by two orders.No matter ordered or disordered,alloying BiOF with BiOCl could broaden the light absorption range and intensity,and further enhanced the photocatalytic efficiency of BiOF_(1-x)Cl_(x)(0<x<1)solid solutions.