Dielectric relaxation and Ac conductivity of perovskites CH3NH3PbX3 (X = Br, I)

MAPbX(3) (MA = CH3NH3, X = Br, I) are synthesized by the chemical route. The Rietveld refinement of the room temperature X-ray diffraction pattern of the materials shows that MAPbBr(3) is crystallized in the cubic Pm3m crystal symmetry whereas MAPbI(3) crystallizes in the tetragonal phase with space group I4/mcm. The dielectric relaxation of MAPbX(3) has been studied in the frequency range from 42 Hz to 0.2 MHz in the electric modulus formalism. The relaxation time is determined by the reciprocal of the frequency where the maximum of the imaginary part of the electric modulus is centred. The relaxation mechanism of the samples is investigated by the Cole-Cole model. The complex impedance plane plots are analyzed by an electrical equivalent circuit consisting of a resistance and a capacitance. The frequency dependent conductivity spectra follow the power law.