Date: 6 July 2018 (Friday)

Time: 10:00 am

Venue: B5207, Yeung Kin Man Academic Building

The discovery and deployment of multifunctional materials such as ferroelectrics have led to paradigm shifts in technologies. Ferroelectrics, a major class of high-coupling materials characterized by the switchable polarization, have become pervasive in modern devices ranging from medical ultrasound, thermal energy harvester, and solid-state refrigerator, to vibration-powered electronics. The device functionalities heavily rely on the dynamical interactions between the electric polarization and applied stimuli (e.g., electric fields). Understanding the materials chemistry/physics of ferroelectrics in response to external perturbations is therefore crucial for accelerated materials discovery and development of ferroelectrics. In this talk, I will cover a multiscale computational approach that combines methods at different length and time scales to elucidate the connection between chemical compositions, local structures, and dynamical properties of ferroelectrics. I will then present a theory-experiment collaboration wherein we demonstrated deterministic and repeatedly obtainable multistate polarizations in ferroelectric thin films, highlighting the potential of ferroelectrics for adaptive neuromorphic electronics to design "brain-like" computers. At the end, I will explain the negative piezoelectric effect, an unusual structural response in which a polar material contracts rather than expands in the direction of the electric field. By screening through a first-principles-based database of piezoelectrics of nearly 1000 inorganic compounds, we identified 93 materials possessing the negative response, showing that such counterintuitive effect is a general phenomenon.

Biography

Shi Liu graduated in 2009 with a B.S. in Chemical Physics from the University of Science and Technology of China, before completing his Ph.D. in Chemistry at the University of Pennsylvania in 2015. During the Ph.D. program, he worked under the direction of Professor Andrew M. Rappe, developing and applying predictive multiscale modeling techniques that combine methods at different length and time scales to understand the dynamics of ferroelectric materials from the atomistic level all the way up to the mesoscopic length scales. Dr. Liu's research interests also involve free radical reactions in polymerization, topological insulators, and organic-inorganic hybrid perovskites. He was awarded the 2015 Professor John G. Miller Award for the Best Thesis in UPenn Chemistry. Following completion of his Ph.D., Dr. Liu was offered a Carnegie Fellowship at the Carnegie Institution for Science in Washington, D.C., where he worked with Dr. Ronald E. Cohen on multiscale simulations of defects in ferroelectrics and hybrid perovskites for photovoltaic applications. He received the American Physical Society 2017 Nicholas Metropolis Award in Computational Physics. He was recently awarded 2018 SEDD (Sensors and Electronic Device Directorate) Distinguished Postdoc

Fellowship at U.S. Army Research Laboratory.

Enquiry:

Department of Materials Science and Engineering

Email: mse@cityu.edu.hk

Tel: 3442 2985