The Growth And Properties Study Of Molecular Ferroelectrics And Switchable Dielectric Materials

Ferroelectrics are a class of highly desirable intelligent materials and play important roles in information storage,microelectronics,remote sensing,which promotes the rapid development of the electronic information industry.The ferroelectrics can't be replaced because of unique characteristics including dielectricity,SHG,pyroelectricity,piezoelectricity,P-E hysteresis.At present,the applications are mainly limited to be based on the conventional oxide materials such as BaTiO3,PbTiO3 and PbZrxTi1-xO3.However,the expensive productive process and the resulting toxic substances can't cater to the necessary of the next-generation devices.Molecular ferroelectrics own more advantages such as controllable design and synthesis,solution processability,nontoxicity and flexibility,which greatly attracted people's attention.Most ferroelectrics can undergo ferroelectric phase transitions,and the resulting unique phenomena can be used to determine whether the material belongs to ferroelectrics.As the external conditions change,molecular switchable dielectric material can switch between the high dielectric state and the low dielectric state,which also owns advantages of molecular materials.It is an effective method to design and synthesize some dielectrics,and then use experiments to select the potential molecular ferroelectrics or switchable dielectric materials.In this work,a new molecular ferroeletcrics and two potential switchable dielectric materials will be studied.The study would be divided into two parts:The first part:Molecular ferroelectrics pyridine-4-ylmethanaminium?1?has been found and studied.1 was discovered undergoing ferroelectric-ferroelectric phase transition at 255.9 K and paraelectric-ferroelectric phase transition at 258.4 K.Because of the small-amplitude anomalies of the dielectric constants and the high pyroelectric coefficient values,the ferroelectric-ferroelectric phase transition of 1 shows two ultrahigh pyroelectric figures of merit?FOMs?with M₁ = 0.16 cm²/?C and M₂ = 0.21 cm^3/2·J^-1/2.The ultrahigh FOMs could make 1 a potential element of the sensitive small-area pyroelectric detectors or pyroelectric vidicons.The second part:Two potential molecular switchable dielectric materials have been found and studied.Blue compound?2?can crystallized from the solution of methanol solvent,which contains pyrrolidine,hydrochloric acid and CoCl2 with the mole ratio of 1:1:1.Compound 2 undergoes a reversible phase transitions above room temperature which is accompanied by obvious ladder-like dielectric anomalies,however,it should go through a heating process at first.The obvious ladder-like dielectric anomalies make 2 a potential switchable dielectric material.Compound 3 can crystallized from the solution of methanol solvent,which contains Dabco and benzoic acid with the mole ratio of 1:1.Compound 3 undergoes ladder-like reversible dielectric phase transitions at 235 K.However,the dielectric anomalies of cooling process are much larger than that of heating process.It may be an effective way to improve the dielectric response of phase transition through improving the quality of crystal 2.