Spectroscopic Study of Structural Phase Transition and Dynamic Effects in a [(CH3)2NH2][Cd(N3)3] Hybrid Perovskite Framework

• Published in: Journal of physical chemistry. C 2019-05, Vol.123 (18), p.11840-11849
• Main Authors: Trzebiatowska, Monika, Mączka, Mirosław, Ptak, Maciej, Giriunas, Laisvydas, Balciunas, Sergejus, Simenas, Mantas, Klose, Daniel, Banys, Juras
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.9b01121

We present a combined study of a [(CH3)2NH2]­[Cd­(N3)3] hybrid perovskite dense metal–organic framework by infrared (IR), Raman, continuous-wave electron paramagnetic resonance (CW EPR), phase-transition-induced current, and dielectric measurements. The Raman and IR studies have shown that the phase transition observed near 175 K is associated with a pronounced narrowing and intensity increase of bands related to the NH2 group of dimethylammonium (DMA+) cations located in the cavities of the framework. This observation has proved that the phase transition is associated with an ordering of DMA+ cations. The dielectric response of the [(CH3)2NH2]­[Cd­(N3)3] single crystal has revealed a weakly expressed anomalous behavior of the dielectric constant at the phase transition point. In the low-temperature phase, a pronounced dispersion in the kilohertz frequency range has been observed, which might be assigned to the twofold reorientation dynamics of the DMA+ cations. The phase-transition-induced current measurements of the DMACd­(N3)3 single crystal reveal a small anomaly at the phase transition temperature, demonstrating a nonferroelectric behavior. The CW EPR experiments of manganese-doped DMACd­(N3)3 disclose that the paramagnetic Mn2+ probe ions have been successfully incorporated in the crystal structure and form MnN6 octahedra. The temperature evolution of the CW EPR spectrum reveals that these centers are sensitive to the structural changes of the cadmium-azide framework occurring during the phase transition. The temperature evolution of the spin Hamiltonian parameters and CW EPR linewidth of the Mn2+ ions have allowed the detection of the effects of the DMA+ cation dynamics and characterization of the type of the phase transition.