Biography
Prof. Sohini Kar-Narayan is Professor of Device & Energy Materials at the Department of Materials Science & Metallurgy at the University of Cambridge since 2018, prior to which she was appointed as a University Lecturer in the same department since 2015. She received a BSc (Honours) in Physics in 2001 from the University of Calcutta, India, followed by MS (2004) and PhD (2009) in Physics from the Indian Institute of Science, Bangalore. Following a postdoctoral appointment at the Department of Materials Science in Cambridge, she was awarded a prestigious Royal Society Dorothy Hodgkin Fellowship in 2012, marking the beginning of her independent research group. Prof. Kar-Narayan is interested in functional nanomaterials for applications in energy, sensing and bio-medicine.
Research
Ferroelectric materials for cooling and energy applications
My research within the Device Materials Group aims at developing an efficient and clean solid-state cooling technology based on the electrocaloric (EC) effect associated with phase transitions in ferroelectric materials. My interest lies in the development and understanding of new EC materials and the subsequent design of prototype cooling devices. Additionally, the piezoelectric and pyroelectric properties of these EC materials are attractive for energy harvesting applications.
Electrocaloric refrigeration
Electrocaloric (EC) refrigeration is a candidate for solid-state cooling that exploits electric field‑driven temperature/entropy changes near phase transitions in ferroelectric materials. There has been renewed interest in the field of electrocalorics since the discovery of giant EC effects (~12 K) in ferroelectric thin films, prior to which EC temperature changes were restricted to a few Kelvin in bulk ferroelectrics. This enhancement arises as thin films possess order-of-magnitude larger breakdown fields than in the bulk. However, reports of large EC temperature changes in films have mostly been predicted from indirect thermodynamic analysis of electrical data. These predictions are difficult to confirm via conventional thermometry/calorimetry as films cannot pump significant heat due to low thermal mass. We are focusing on novel techniques to accurately measure the EC effect in thin films of promising materials, and on modeling EC heat flow, to provide a basis for developing optimized EC devices for cooling applications.
Energy harvesting
Energy harvesting for small power applications is a hot research topic due to its potential applications in powering portable electronics, wireless sensors and medical implants, to name a few. Fixed energy sources such as batteries and fuel cells are the most commonly used power sources, but have serious disadvantages such as the constant need for replacing and recharging due to their short lifetime, and their size which does not scale with the diminishing sizes of modern electronic devices. Powering devices from scavenged ambient energy from the environment is an attractive avenue for replacing or extending the lifetime of traditional power sources. Our research in this area entails scavenging energy from mechanical vibrations and temperature variations of ambient environments using the piezoelectric and pyroelectric properties respectively of ferroelectric thin films and multilayer capacitors.
