Modellierung des elektrokalorischen Effekts in bleifreien Relaxor Ferroelektrika (DFG Priority Programme 1599 (SPP))
Lead-free relaxor ferroelectrics are promising candidate materials for achieving a large electrocaloric effect (ECE) at rather low electric fields.
In this subproject the polarization switching and the ECE of lead-free relaxor ferroelectrics will be computationally investigated by using both atomistic and continuum models. We will combine first-principles methods (DFT), molecular dynamics (MD) and phase-field approaches through free-energy and entropy calculations, that are based on Monte-Carlo (MC) simulations using effective Hamiltonians. For simulating the hysteresis behavior and the ECE in ferroelectric relaxors, the phase field theory and a Monte Carlo method will be employed. Simulations results are meant for prediction of the ECE of the materials. Continuum modeling based on the Landau free energy and the phase field simulation will be used to simulate the switching and domain structure evolution in ferroelectric relaxors.
Alternatively, we will make use of the Maxwell relation and express the temperature change and/or the isothermal entropy change. Correlation between the temperature dependent hopping probability and the domain switching will be analyzed. Influence of the exact role of the claimed polar nanoregions will be investigated.
Effects of domain structures on the ECE will be also studied by the Landau free energy approach. The formation preconditions of the ECE, i.e. whether the ECE prefers to occur above or below paraelectric to ferroelectric phase transitions, is particularly of interest. Special focuses will be given to the influence of strain/stress and the material parameters.
Fähler, S., Rößler, U. K., Kastner, O., Eckert, J., Eggeler, G., Emmerich, H., Entel, P., Müller, S., Quandt, E. and Albe, K. (2012), Caloric Effects in Ferroic Materials: New Concepts for Cooling. Adv. Eng. Mater., 14: 10–19. doi: 10.1002/adem.201100178