Lead-Free Hybrid Material with an Exceptional Dielectric Phase Transition Induced by a Chair-to-Boat Conformation Change of the Organic Cation.

Hybrid organic-inorganic perovskite materials have demonstrated great potential in the field of photovoltaics and photoelectronics. On the basis of the high degree of structural flexibility and compatibility, diverse molecular functional materials have been assembled by modifying the length of the organic components and/or dimensionality of the inorganic frameworks. In this paper, we present a chiral lead-free organic-inorganic hybrid, (piperidinium)SbCl (1), which follows the one-dimensional inorganic frameworks of the corner-sharing SbCl octahedra. Strikingly, 1 displays a dielectric phase transition at T = 338 K, changing from the chiral space group of P222 to polar Pna2 upon heating. Crystal structure analyses reveal that an unusual thermally activated conformation change of the piperidinium cations affords the driving force to the phase transition of 1. That is, organic piperidinium moieties display a chairlike conformation below T, which transforms to a boatlike structure above T. Such an unprecedented change is strongly coupled to the dielectric transition along with notable steplike anomalies, which suggest that 1 could be used as a potential switchable dielectric material. Besides, the temperature-dependent conductivity and theoretical analysis of its electronic structure disclose the semiconducting behavior of 1. This study paves the pathway to the design of new lead-free semiconducting perovskites with targeted properties for optoelectronic application.