First principles calculation of optical absorption and polarization properties of In doped <i>h</i>-LuFeO₃

The h -LuFeO 3 is a kind of narrow band gap hexagonal ferrite material, with a good application prospect in the field of ferroelectric photovoltaic. However, the low polarization intensity of h -LuFeO 3 makes the recombination rate of photogenerated electrons and holes large, which is not conducive to the improvement of the efficiency of h -LuFeO 3 -based ferroelectric photovoltaic cells. In order to improve the ferroelectricity and optical absorption properties of h -LuFeO 3 , the first principles method is used to calculate the doping formation energy values of In atom at different positions of h -LuFeO 3 , and the most stable doping position is determined. The comparisons of band gap, optical absorption performance and polarization intensity among h -Lu 1- x In x FeO 3 ( x = 0, 0.167, 0.333, 0.667) are made. With the increase of In doping, the cells of h -Lu 1– x In x FeO 3 stretch along the c -axis. The ratio of the lattice constant c / a increases from 1.94 at x = 0 to 2.04 at x = 0.667 when all the positions of In replace P1 position. Using the qualitative calculation of Berne effective charge, the results show that the ferroelectric polarization intensity of h -LuFeO 3 , h -Lu 0.833 In 0.167 FeO 3 , h -Lu 0.667 In 0.333 FeO 3 and h -Lu 0.333 In 0.667 FeO 3 along the c -axis are 3.93, 5.91, 7.92, and 11.02 μC·cm –2 , respectively. Therefore, with the increase of the number of In atoms replacing Lu atoms, the lattice constant c / a ratio of h -Lu 1– x In x FeO 3 increases, which can improve the ferroelectric polarization strength of the material. By analyzing the density of states of h -LuFeO 3 and h -Lu 0.333 In 0.667 FeO 3 , we can see that In doping enhances the Fe-O orbital hybridization in h -Lu 0.333 In 0.667 FeO 3 , and makes the optical absorption coefficient of h -Lu 0.333 In 0.667 FeO 3 in the solar light range larger. In summary, In doped h -LuFeO 3 is an effective method to improve its polarization intensity and optical absorption coefficient, which is of great significance for improving the performance of ferroelectric photovoltaic.