Evidence for Ferroelectricity of All-Inorganic Perovskite CsPbBr3 Quantum Dots

The combination of ferroelectric-optical properties in halide perovskites has attracted tremendous interess because of its potential for optoelectronic and energy applications. However, very few reports focus on the ferroelectricity of all-inorganic halide perovskites quantum dots. Herein, we report a excellent ferroelectricity in CsPbBr3 quantum dots (QDs) with a saturation polarization of 0.25 mu C/cm(2). Differential scanning calorimetry, X-ray diffraction, and transmission electronic microscopy revealed that the mechanism of ferroelectric-paraelectric switching of CsPbBr3 QDs can be attributed to the phase transition from cubic phase (Pm (3) over barm) to the orthorhombic phase (Pna2(1)). In the orthorhombic CsPbBr3, the distortion of octahedral [PbBr6](4-) structural units and the off-center Cs+ generated the slightly separated centers of positive charge and negative charge, resulting in the ferroelectric properties. The variable-temperature emission spectrum from 328 to 78 K exhibits green luminescence and a gradual red shift due to the phase transition. This finding opens up an avenue to explore the ferroelectric-optical properties of inorganolead halide perovskites for high-performance multifunctional materials.