The Growth And Properties Of Organic Ferroelectrics With 4-aminopyridinium Cation

Ferroelectrics,as a kind of multifunctional materials,have a spontaneous electric polarization below the Curie temperature,which can be reversed by an external electric field.Its outstanding characteristics make ferroelectrics to be the one of promising candidates in the fields of electric random access memory,ferroelectric field-effect transistors,piezoelectric devices,nonlinear optical devices,capacitors,pyroelectric infrared detectors,and pyroelectric vidicons.Among the numerous ferroelectrics,organic ferroelectrics have drawn greater attention due to their unique advantages,such as easy and environmentally friendly processing,especial lightweight and mechanical flexibility,which make it more competitive to be applied to medical,micromechanical,and biomechanical field or industry.The history of organic ferroelectrics can be traced back to the discovery of Rochelle salt in 1920 by Valasek.Nevertheless,the organic ferroelectrics were not abundant until recent decades.Since diisopropylammonium bromide was reported to have a spontaneous polarization as large as that of BaTiO3(a famous inorganic ferroelectric),an army of new organic ferroelectrics have sprung up,such as MDABCO(N-methyl-N'-diazabicyclo[2.2.2]octonium)-ammonium triiodide,[S-l-(4-chlorophenyl)ethylammonium]2PbI4,and so on.The transition of 4-Aminopyridinium Perchlorate,used to be known as a pyroelectric below 246 K,remained a mystery to us unitl the high-quality crystal of APP has grown now.In this work,we conducted further study and discussion on the derivatives of 4-Aminopyridinium,which contains the following two parts:Part one:4-Aminopyridinium Perchlorate(APP)is first discovered to be a new molecular ferroelectric in this work.Owing to the dramatic changes of the protonated cations and order-disorder of anions,the crystal symmetry of APP transforms from P21/c to P21 in this first-order phase transition.As a result,APP is also found to have a perfect electric hysteresis loops with a large spontaneous polarization of 1.0 ?C/cm2 and a small coercive field of 0.67 kV/cm below 246 K,which is revealed by other measurements,such as differential scanning calorimetry,heat capacity,dielectric anomalies and Raman spectrum.Part two:As another one of derivatives of 4-Aminopyridinium,4-Aminopyridinium Iodide(API),was found to have the activity of ferroelectics.API has a beautiful electric hysteresis loops with a larger spontaneous polarization of 1.4 ?C/cm2 and a really tiny coercive field of 0.5 kV/cm below the temperature of ferro-para transformatin at about 276 K.Moreover,the dieletric content of API would change diffusely depand on the frequency,which is in accordance with the property of relaxation ferroelectrics.