Synthesis And Properties Study Of Hexagonal Heterocyclic Molecular Ferroelectrics

Ferroelectric is a kind of multifunctional polar material due to its dielectric,piezoelectric and pyroelectric effects.These properties make it widely used in intelligent switches,sensors and other fields of intelligent electronic devices.At present,inorganic ferroelectrics containing lead and other heavy metals are mainly used.Their production costs are high,and their production will pollute the environment with toxic and harmful substances.Molecular-based ferroelectrics is a branch of ferroelectrics.It can avoid the shortcomings of inorganic ferroelectrics.It is not only low-cost and environmentally friendly,but also easier to fabricate devices for intelligent wearable devices.Therefore,it has great potential to replace inorganic ferroelectrics as new star materials.In this paper,we focus on how to design and synthesize new molecular-based ferroelectric materials,and try to find practical molecular ferroelectric materials with superior performance.Starting from the hexagonal heterocyclic,three hexagonal heterocyclic compounds were selected according to the controllable characteristics of molecular ferroelectrics,four new molecular ferroelectrics were synthesized,and their ferroelectric properties were characterized.The main contents of the paper are divided into three parts:The first part:A new piperidyl-based molecular ferroelectric piperidine-4-ylmethanaminium perchlorate(compound 1)has been successfully synthesized,which is ferroelectric below Tc = 258.8K and undergoes a ferroelectric phase transition at Tc.The spontaneous polarization of compound 1 is 0.63 p.C/cm2,and the coercive field is 1.14 kV/cm at temperature of 192 K.The ladder-like dielectric behavior reveals that it is a potential switchable dielectric material.X-ray diffraction reveals that the space group from LTP to HTP changes from P2,to P212121.By measuring the pyroelectricity and hysteresis loop of compound 1,the ferroelectric properties of the compound 1 were further proved.The second part:A new molecular ferroelectrics pyridin-2-ylmethanaminium perchlorate(compound 2)was discovered,which undergoes a ferroelectric phase transition around 264.8 K.The spontaneous polarization reaches 0.22?C/cm2 and the coercive fields as small as 1.1 kV/cm at 202 K.Single-crystal X-ray diffraction reveals that the space group transforms from a polar space group of P21 at 173 K to a centrosymmetric space group of P21/c at 293 K.By analyzing the crystal structure changes below and above the phase transition temperature,it can be concluded that the phase transition induced by disorder of perchlorate.Its ferroelectricity was confirmed by measurements of differential scanning calorimetry,dielectric and hysteresis loop.The third part:A hexagonal heterocyclic compound 1,4-dimethylpiperazine,which is similar to DABCO and has high symmetry,was selected to synthesize two new ferroelectrics 1,4-dimethylpiperazine perchlorate(3)and 1,4-dimethylpiperazine fluoroborate(4),respectively.Ferroelectrics 3 has a very low Curie temperature(207.6K),one of its molecules contains a crystalline water,and organic solvents are more conducive to its crystal growth.Ferroelectrics 4 has a very high spontaneous polarization(7.4?C/cm2),which is much higher than the previous three ferroelectrics and higher than most molecular-based ferroelectrics.One of its molecules contains two crystalline waters.This section simply verifies the ferroelectric properties of these two ferroelectrics,and there are many other related properties that can be studied.