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The temperature-dependent structure of crystalline methylammoniumtrihalogenoplumbates (II)—CH3NH+3PbX−3 (X=Cl, Br, I)—as determined by x-ray diffraction, is compared with measurements of the temperature-dependent complex permittivity at frequencies of 50–150 GHz. The dielectric measurements reveal a picosecond relaxation process which corresponds to a dynamic disorder of the methylammonium group in the high-temperature phases of the trihalogenoplumbates.
Poglitsch et al. (Tue,) studied this question.