Near-room-temperature tunable dielectric response induced by dual phase transitions in a lead-free hybrid: (C3H8N)2SbBr5

Abstract

Organic–inorganic hybrid materials, which exhibit structural diversity and rich physical properties, have shown great potential as basic device elements in the optoelectronic field. Herein, we report a new lead-free organic–inorganic hybrid compound, [C₃H₈N]₂SbBr₅ (1, where C₃H₈N⁺ is the cyclopropylammonium cation), which demonstrates tunable dielectric responses near room temperature, derived from its two successive structural phase transitions at the vicinity of T₁ = 290 K and T₂ = 315 K, respectively. That is, its dielectric constants change from high-dielectric (above T₂), moderate-dielectric (between T₂ and T₁) and low-dielectric states (below T₁). Such dielectric behaviors coincide well with a series of reversible thermal peaks in the DSC curve. Further structural analyses reveal that the order–disorder of organic cationic moieties accounts for the phase transition at T₂, while the change of the molecular configuration provides the driving force to the phase transition at T₁. Such phase transition behaviours differ from those of the majority of previously reported dielectric phase transition materials. Moreover, theoretical calculation of the electronic band structure of 1 reveals the direct feature with a band-gap value of ∼2.36 eV. This work affords broader design flexibility for the future exploration of electrically-ordered materials in the organic–inorganic hybrid family.