Dielectric studies on CH3NH3PbX3 (X=Cl and Br) single crystals

Dielectric dispersion measurements have been performed on CH3NH3PbX3 (MAPbX(3), X = Cl and Br) single crystals at frequencies between 50 Hz and 1 MHz. Significant dielectric dispersion was observed in the cubic and tetragonal II phases for MAPbCl(3) and in the cubic, tetragonal I and tetragonal II phases for MAPbBr(3). The apparent dielectric dispersion was attributed to the ionic conductivity in the crystals. The static bulk conductivity was expressed by the Arrhenius-type formula sigma = (A/T) exp(-Delta E/kT). The activation energies for the ionic conduction along [100] axis for each phase are estimated to be 0.13 eV (cubic phase) for MAPbCl(3) and 0.132 eV (cubic phase) and 1.60 eV (tetragonal I phase) for MAPbBr(3).