Structural phase transition, electrical and semiconducting properties in a lead-free 2D hybrid perovskite-like compound: [Cl-(CH2)(2)-NH3](2)[CuCl4]
Résumé
A new layered perovskite-type organic-inorganic hybrid compound [Cl-(CH2)(2)-NH3](2)[CuCl4] (1), in which 2-chloroethylammonium cation occupies the space enclosed by the CuCl6 octahedra, has been successfully synthesized. It is found that the compound exhibits the semiconducting properties with the optical band gap equal to 1.98 eV, confirmed by AC conductivity measurements, which varies between 10(-5) and 10(-4) omega(-1) m(-1). Also, the low activation energy at low temperatures (0.26 eV) can indicate the electronic conduction of this material. Compound (1) displays phase transitions at T-1 = 281 K and T-2 = 380 K, confirmed by DSC, electrical and dielectric measurements. Single-crystal X-ray diffraction data at variable temperatures reveal that symmetry-breaking occurs from P2(1)/c (at 296 K > T-1) to P-1 (at 150 K < T-1), originating directly from the [Cl-(CH2)(2)-NH3](+) cation conformational changes and the distortions of CuCl64- octahedra caused by the Jahn-Teller effect in the inorganic layers. Meanwhile, organic 2-chloroethylammonium moieties display some boat-like conformation below T-1, which transforms to a chair-like structure above T-1. This study paves the pathway to explore new lead-free hybrid perovskites with targeted properties for thermoelectric, supercapacitors, batteries, environmentally friendly processing and semiconductor applications.