【摘要】 获得窄的带隙和大的极化强度是提高铁电光伏材料性能的关键。本文采用第一性原理方法,研究了S掺杂对SnTiO₃带隙和极化强度的影响。通过计算两种最可能的替换掺杂位置,确定了稳定的SnTiO_3-xS_x掺杂结构。研究发现,S的掺杂会引起SnTiO₃沿c轴拉伸,使c/a值变大,带隙宽度变小,极化强度变大。SnTiO_3-xS_x在x=0. 33和x=0. 5时的带隙相同,此时S掺杂量的改变并没有引起带隙的变化;但S掺杂量增加到x=1时（即SnTiO₂S）具有金属性。进一步的态密度分析表明,S适量掺入后与Ti和Sn成键,降低了Ti的非占据态能量,导带的Ti 3d轨道向低能级移动,从而使掺杂SnTiO₂S的带隙由SnTiO₃的1. 87 e V降低到1. 01 e V。通过Bader电荷分析SnTiO₂S带隙降低的原因,结果显示,S的引入导致SnTiO₂S中离子电荷的总数变小,体系整体电离度变弱,从而引起带隙变小。使用Berry相方法计算表明,随着掺杂量的增加,SnTiO_3-xS_x的极化强度也会增加。本工作从理论上预测S掺杂能够降低无Pb材料SnTiO₃的带隙并使其保持大的极化强度,为改善SnTiO₃的铁电光伏特性提供了一种有效手段。更多还原

【Abstract】 The narrow bandgap and the large polarization play important roles to improve the ferroelectric photovoltaic properties of ferroelectric materials. In this work,the effects of S doping to the bandgap and polarization of the Pb-free SnTiO₃ are investigated. The stable structure of SnTiO_3-xS_xis obtained by the calculation of the two possible S doping sites. It is found that the c axils would be stretched to induce the increase of c/a,and to obtain the narrow bandgap and the large polarization. The bandgaps of SnTiO_3-xS_xis nearly same when x is 0. 33 and 0. 5. However,the SnTiO₂S is not semiconductor but metal when x = 1. Furthermore,the density of states analysis demonstrates that the energy of unoccuping state of SnTiO₂S reduced comparing with SnTiO₃ when S atom bond with Ti and Sn atom after S doping. The bandgap of Sn TiO₂ S decrease as the Ti 3 d ortitals moves to the lower energy. Bader charge analysis shows that the total ionizability of Sn TiO₂ S is lower than SnTiO₃,inducing the bandgap decrease of SnTiO₂S. The polarization of SnTiO_3-xS_x increases with the increase of S doping by the Berry phase method. In this work,it is predicted that the narrow bandgap and the large polarization of Pb-free SnTiO₃ can be obtained by the S doping. It provides an effective way to improve the ferroelectric photovoltaic properties of SnTiO₃.更多还原