Exploiting microstructure and symmetry in new ferroelectric materials

Abstract

Ferroelectric materials exhibit naturally occurring electronic polarization states, inspiring a wide array of potential use and function in technology. Charge separation from internal fields and the bulk photovoltaic effect are promising properties for photo-current generation, and control over the orientation of ferroelectric polarization allows for non-volatile memory storage. Coupling ferroelectricity to other properties of symmetry, as in multiferroics, provides an external knob which can be used to tune such material properties as the crystal structure, band gap, and spin via the electric field; great for sensor and spintronic applications. Real-world application of ferroelectric materials is hindered however by their insulating nature; where larger band-gaps discourage photo-absorption. Semiconducting materials whichmaintain ferroelectricity are therefore highly desired. In this work I present research done on the ferroelectric materials Silver-Bismuthate (Ag2BiO3) and Cyclohexylethylamine-Triiodo-Plumbate ([CYHEA]PbI3). In addition to first principles calculations, a phase field model was developed and used to simulate larger scale effects of microstructure such as domain formation and hysteresis. [CYHEA]PbI3 is a new class of chiral-ferroelectric, akin to a multiferroic in how it couples broken symmetry in a single material. Coupling of chirality and ferroelectricity could lead to properties such as selective domain switching or optical force generation, and could find use in spintronic applications. Ag2BiO3 represents a charge-disproportionate ferroelectric, a class of materials which shows promise in photovoltaic applications. Of particular interest with this material is the presence of a Weyl semimetallic state, which is shown here to possibly be stabilized in a polar domain interface.