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

Abstract

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.

Dimensional Reduction of Cs2AgBiBr6: A 2D Hybrid Double Perovskite with Strong Polarization Sensitivity

“…As shown in the band structures diagram (Figure 2 b), the bottom of conduction band locates at the S point, while the topmost of valence band is at the G point, revealing its indirect band gap feature. [17] The value of band gap from band structure calculation is about 2.35 eV, in accordance with our experiment value. From the partial density of states (PDOS), we can assert AgBr 6 and BiBr 6 octahedra dominate the optical band gap of 1, since the orbital states near the Fermi level mainly derive from the inorganic octahedra (Supporting Information, Figure S5).…”

A Metal-Free Molecular Antiferroelectric Material Showing High Phase Transition Temperatures and Large Electrocaloric Effects

“…The relatively large thermal hysteresis discloses the first-order feature for the phase transitions. In addition, the number of the possible molecular orientations ( N ) can be estimated to be 2.05 from the Boltzmann formula Δ S = nR ln N (where n is the number of guest molecules per mole and R is the gas constant), which reveals the typical order–disorder phase transition ( N = 2) . In addition, the variable-temperature PXRD measurements also verify the occurrence of its successive phase transitions, as shown in Figure S4.…”

Switchable Dielectric Behavior and Order‐Disorder Phase Transition in a New Organic‐Inorganic Hybrid Compound: (CH3NH3)4[InCl6]Cl

“…Based on the DSC curves, the associated entropy change Δ S was estimated with a value of 2.74 J/mol K for the phase transition at 284 K. According to the Boltzmann equation Δ S = R ln ( N 1/ N 2), in which R denotes the gas constant 8.314 and N 1 and N 2 are the numbers of independent directions of motion in the HTP and LTP. During cooling, the result showed that N = 1.39, manifesting a more complicated phase transition rather than the order‐disorder mechanism ( N = 2), the structural analysis will further confirmed it.…”