Keynote
BENDING MATERIALS TO OUR WILL: THE MATERIALS DESIGN OF FERROELECTRICS THROUGH COORDINATED THEORY AND EXPERIMENTATION

Ferroelectric materials offer compelling fundamental physical challenges and outstanding promise for applications, only some of which has been realized. Recently, a new paradigm for research in this field has emerged along with a new perception of its relationship to other fields. In particular, new experimental techniques have illuminated the extent and the limitations of analogies between ferroelectrics and other functional materials including ferromagnets, glasses, liquids, and liquid crystals. A consensus view may be that these analogies are all helpful but incomplete, leaving ferroelectrics as a class with unique properties. Signature features include strong and competitive interactions on different length scales, as well as coexisting long-range order and strong disorder.

Theoretical researchers have adopted and modified analytical techniques that originated in related disciplines, synthesizing them to create refined tools well suited to describe and understand the complexity of ferroelectrics. This includes elements of critical phenomena and phase transition theory, solid-state physics, crystal chemistry, theory of liquids, and nucleation and growth theory. On the one hand, this state of affairs could be considered idiosyncratic and perhaps nearly incomprehensible to those entering the field. Instead, I will put forward the view that ferroelectrics serve as the crossroads of materials science, chemistry, and physics.

In this lecture, several areas of contemporary ferroelectric research will be highlighted, in order to illustrate the integrated research paradigm described above, with emphasis on the relationships between physical mechanism and materials design as well as between theory and experiment. The dynamics of ferroelectric domain walls has seen great progress in the last decade. I will discuss these developments, with focus on current perceptions of how walls move and how they influence material properties. The relaxor ferroelectrics are perhaps the epitome of complexity, offering multiple length and time scale dynamics. I will talk about recent work in this field, including new understanding of the formation and behavior of polar nanoregions. An exciting materials design challenge has been the search for ferroelectric photovoltaics, and I will provide a report of progress toward materials with strong visible light absorption and photocurrent generation. As an extension of this, I will comment on connections between ferroelectricity in oxides and hybrid perovskites. Beyond bulk phenomena, I will highlight interesting developments in the area of interfaces between ferroelectrics and other active systems, including graphene and molecular fluids. The commonalities in physical mechanism and applicable synthesis and characterization techniques in these functional systems offer enhanced prospects for integrated electronics and optoelectronics, in which ferroelectrics concurrently play many roles.