High-Temperature Molecular Ferroelectric Tris(2-hydroxyethyl) Ammonium Bromide with Dielectric Relaxation.

We obtained one new molecular ferroelectric material tris(2-hydroxyethyl) ammonium bromide () that crystallizes in aqueous solution at room temperature with a space group of 3 which belongs to ten polar space groups. There is a paraelectric-to-ferroelectric phase transition at 424 K (from hexagonal 3̅ to hexagonal 3 phase). Such a high transition temperature is close to that of diisopropylamine bromide (426 K) and higher than that of many other molecular ferroelectrics, such as triethylmethylammonium tetrabromoferrate(III) (360 K); some of the organic-inorganic perovskite ferroelectrics, such as (cyclohexylammonium)PbBr (363 K); and some inorganic ferroelectrics, including BaTiO (393 K).

Ferroelectricity of the Orthorhombic and Tetragonal MAPbBr Single Crystal.

Hybrid organic-inorganic halide perovskites (HOIPs) MAPbBr and their ramifications have emerged because of the photovoltaic, optical, and other fascinating performances of HOIPs in recent years. However, many intrinsic properties, such as crystal structure and ferroelectricity, are still controversial. In this work, the ferroelectricity of the orthorhombic and tetragonal MAPbBr single crystal was confirmed through the dielectric behavior versus bias electric field ε( E), the temperature-dependent pyroelectric current with positive/negative poling, and the positive-up-negative-down (PUND) measurements.