Exploring a lead-free organic-inorganic semiconducting hybrid with above-room-temperature dielectric phase transition.

Yuyin Wang,Yaobin Li,Dhananjay Dey,Zhihua Sun,Shiguo Han,Xitao Liu,Junhua Luo,Zhenyue Wu

doi:10.1039/c9ra09289g

Abstract

Recently, organic–inorganic hybrid lead halide perovskites have attracted great attention for optoelectronic applications, such as light-emitting diodes, photovoltaics and optoelectronics. Meanwhile, the flexible organic components of these compounds give rise to a large variety of important functions, such as dielectric phase transitions. However, those containing Pb are harmful to the environment in vast quantities. Herein, a lead-free organic–inorganic hybrid, (C6H14N)2BiCl5 (CHA; C6H14N+ is cyclohexylaminium), has been successfully developed. As expected, CHA exhibits an above-room-temperature solid phase transition at 325 K (Tc), which was confirmed by the differential scanning calorimetry measurement and variable temperature single crystal X-ray diffraction analyses. Further analyses indicate the phase transition is mainly governed by the order–disorder transformation of organic cyclohexylaminium cations. Interestingly, during the process of phase transition, the dielectric constant (ε′) of CHA shows an obvious step-like anomaly, which displays a low dielectric constant state below Tc and a high dielectric constant state above Tc. Furthermore, variable temperature conductivity combined with theoretical calculations demonstrate the notable semiconducting feature of CHA. It is believed that our work will provide useful strategies for exploring lead-free organic–inorganic semiconducting hybrid materials with above room temperature dielectric phase transitions.

Highlights

Solid state switchable dielectric materials have attracted great attention due to their signi cant roles in signal processing, phase shi ers, data communication, varactors and sensors, etc.[1,2,3,4,5,6,7,8] It is known that the dielectric constant re ects the electric polarizability of a material, which relates to the dipole movement such as molecular rotation
Polar molecules in the solid state usually show smaller electric permittivities than in the liquid state because of the “freezing” and “melting” of the molecular reorientations, which respectively corresponds to a low temperature phase (LTP) and a high temperature phase (HTP), which makes phase transition materials promising candidates as new dielectric switches
The large heat hysteresis of 8 K is indicative of the discontinues rst-order one.[33]

Summary

Introduction

Solid state switchable dielectric materials have attracted great attention due to their signi cant roles in signal processing, phase shi ers, data communication, varactors and sensors, etc.[1,2,3,4,5,6,7,8] It is known that the dielectric constant re ects the electric polarizability of a material, which relates to the dipole movement such as molecular rotation. Polar molecules in the solid state usually show smaller electric permittivities than in the liquid state because of the “freezing” and “melting” of the molecular reorientations, which respectively corresponds to a low temperature phase (LTP) and a high temperature phase (HTP), which makes phase transition materials promising candidates as new dielectric switches. In consideration of practical applications, the optimal phase transition temperature range of dielectric switching materials is between aState Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China cState Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, China † Electronic supplementary information (ESI) available.

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Conclusion