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Abstract

Not only CDW and magnetocaloric materials but also ferroectrics show diffusionless phase transitions related to phonon softening and exceptional functional properties. In these insulating materials various competing instabilities and complex phases separated by martensitic transitions can be tuned by composition and elastic boundary conditions. These transitions are related to enhanced piezoelectric and dielectric responses and allow for a large electrocaloric effect, i.e. adiabatic temperature change in a varying external electrical field, which is promising for novel cooling devices. While ferroelectric phase transitions have been studied for decades and also the understanding of the caloric effect under ideal conditions made important progress in the last years, there are important gaps in knowledge with respect to the electronic and microscopic processes which govern their reversibility, time-stability and tunability [1,2]. Particularly, it is important to understand the impact of the time-dependent microstructure (atomic ordering, defects, domain walls, etc.) on the phase transitions and the functional responses. In this talk I will discuss how ab initio based molecular dynamics simulations allow to isolate these factors and help to predict design rules for ideal microstructures. Thereby I will focus on the coupling between strain, domain structure, and phase transition in prototypical ferroelectric BaTiO 3 [3,4].

References:
[1] A. Grünebohm et al., Energy Technol. 6, 1491, (2018)
[2] A. Grünebohm et al, J. Phys.: Condens. Matter 34, 073002, (2021)
[3] A. Grünebohm et al, Phys. Rev. Mater. 4, 114417 (2020)
[4] A. Everhardt et al, App. Phys. Rev. 7, 011402 (2020)