Ab initio study of metastable layered perovskites $R_2$Ti${}_2$O${}_7$ ($R$ $=$ Sm and Gd)

The structural, electronic, and ferroelectric properties of metastable $R_2$Ti${}_2$O${}_7$($R=$ Sm and Gd) layered perovskites materials are investigated by first-principles density functional theory calculations. The computed structural parameters are found to be in good agreement with experimental findings. The calculated spontaneous polarizations of the studied titanates are found to be larger than the spontaneous polarization of the usual $R$${}_2$Ti${}_2$O${}_7$ layered perovskites materials. GGA+$U$ electronic structures predict a good photocatalytic activity for the studied compounds, in particular for Gd${}_2$Ti${}_2$O${}_7$, which lacks electron-carriers trapping in the conduction band. From the results of the total energy and the polarization as functions of structure we estimate the responses of the materials to external electrostatic fields.

Figure 1

Crystal structure of layered perovskites $R_2$Ti${}_2$O${}_7$.

Figure 2

GGA+$U$ partial densities of states (PDOSs) for SmTO (a) and GdTO (b). Minority-spin states are shown with a negative sign. Zero energy is set to the Fermi level.