Analysis of the low-temperature dielectric relaxation in CH3NH3PbI3 partially substituted with Sn and Ba

In this work, we partially replaced Pb with non-toxic elements to form hybrid perovskites CH 3 NH 3 Pb 0.9 M 0.1 I 3, where M = Sn 2+ and Ba 2+ and studied their dielectric properties. According to room-temperature Rietveld analysis, all compositions with 10 % substitution were tetragonal with a space group I4/ mcm. A notable dielectric relaxation was detected at T similar to 60-100 K, far below the orthorhombic-to-tetragonal phase transition at T similar to 155 K. To clarify the conflicting literature reports, the dielectric relaxation was fitted to both Arrhenius and Vogel-Fulcher models and showed no indication of the finite ( i. e. non-zero) dipolar freezing temperature. It is concluded, therefore, that the low-T dielectric dispersion is a signature of the Debye-type thermally activated re-orientation of the non-interacting electric dipoles with an activation energy of E a similar to 123 -171 meV.