WFD-4 Ferroelectric domain walls: Phenomenology, Local structure, and Probing Methods Venkatraman Gopalan Materials Science and Engineering, Center for Optical Technologies 253 Materials Research Laboratory, Pennsylvania State University University Park, PA 16803 　　　　　Ferroelectrics are widely used today in communications, lasers, precision motion, 　　　　　imaging, and memory applications. This talk will introduce the concept of 　　　　　ferroelectric domain walls and contrast it with ferromagnetic domain walls. Free 　　　　　energy phenomenological description of the wall structure will be developed. The 　　　　　local behavior of the key order parameters, namely, polarization, strain, and their 　　　　　coupling to each other and to other physical properties of the material such as 　　　　　electromechanical and optical properties will be described. A discussion of how the 　　　　　local domain wall properties translate to macro-scale ferroelectric properties will be 　　　　　presented. The role of small amounts of atomic defects in making dramatic 　　　　　differences to nanoscale and macroscale properties will be discussed.