Dynamics and microscopic origin of the electrocaloric effect in relaxor ferroelectrics

• Applicant: Dr. Jörg Rudolph
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 418847609

We will study the complex dynamic behavior of the electrocaloric effect in relaxor ferroelectrics. Direct contactless measurements of the adiabatic temperature change Delta T via detection of thermal radiation will be correlated with below millisecond time-resolved structural data and time-resolved polarization data P(E). The structural and symmetry changes will be sensitively probed by optical second harmonic generation from laser pulses which allows for an extremely fast monitoring of, e.g., the change of polar regions in a material during electric field cycling and of structural fluctuations in thermal equilibrium. The unique combination of all three methods will give new insights into the fast dynamics of the so-called polar nano-regions in relaxor materials that are thought to be responsible for the huge electrocaloric effect in theses materials. Moreover, the slow aging and rejuvenation behavior found in relaxors will be investigated, aiming for guidelines for how to suppress aging in relaxor materials. We will extend the measurement bandwidth to beyond 1 MHz, which will allow us to beat fast heat diffusion into the substrate and to systematically investigate also new electrocaloric materials that (in their early stage of development) are only available as layers or thin-films.

• DFG Programme: Research Grants