Identification of Possible Organoferroelectric Crystals
Mentor:Kimberley Cousins, Professor Organic Chemistry , California State University - San Bernardino
Ferroelectric materials show a spontaneous electric polarization, which can be manipulated by an applied electrical field. Ferroelectric materials have many potential applications, including ultra-high-density memory devices and sensors. Many inorganic ferroelectric materials are well known, while organic ferroelectric crystals are still being discovered and an effective way of identifying them is needed. Organic ferroelectric crystals could be used as an environmentally friendly alternative to their inorganic counterparts because of their lack of heavy metals and potential recyclability. We have developed a method to identify potential ferroelectric crystals from among eight hundred thousand structures in the Cambridge Structural Database (CSD). Organic ferroelectric crystals must be pseudosymmetric; that is, there must exist an accessible structure close in geometry to the original with higher symmetry on a plane nearly orthogonal to the net dipole vector. To develop and test our method, a list of 88 crystalline materials composed of small organic crystals with halide counterions that crystallized in polar space groups was generated. Next, a pseudosymmetric calculation on each compound was performed in order to determine possible phase transitions of the crystal structure to an orientation with higher symmetry. The dipole for the original crystal group was calculated using MOPAC (Molecular Orbital PACkage) and the angle between the dipole and pseudosymmetric plane was determined. Finally a visual comparison of pseudosymetric structures was made to qualitatively determine if the pseudosymmetric shift was feasible. Of the 88 crystals originally tested five were independently rediscovered and had previously been identified as ferroelectric. There are four additional candidates that have been identified as potential organoferroelectric crystals; these are undergoing further calculations prior to synthesis and evaluation.