Analysis of the low-temperature dielectric relaxation in ${\text{CH}}_3{\text{NH}}_3{\text{PbI}}_3$ partially substituted with Sn and Ba

In this work, we partially replaced Pb with non-toxic elements to form hybrid perovskites ${\text{CH}}_3{\text{NH}}_3{\text{Pb}}_{0.9}{\text{M}}_{0.1}{\text{I}}_3$, where $\text{M}={\text{Sn}}^{2+}$ and ${\text{Ba}}^{2+}$ and studied their dielectric properties. According to room-temperature Rietveld analysis, all compositions with 10 % substitution were tetragonal with a space group $I4/\text{mcm}$. A notable dielectric relaxation was detected at $T\sim 60$–$100\text{ K}$, far below the orthorhombic-to-tetragonal phase transition at $T\sim 155\text{ K}$. 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 $E_a\sim 123-171\text{ meV}$.