Understanding pressure-induced depolarization and energy harvesting in ferroelectric and antiferroelectric crystals by fast compression experiments

• Applicant: Dr. Lkhamsuren Bayarjargal
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 468566236

Ferroelectric materials can release very large amounts of stored electrical energy in a very short time scale as pressure-induced phase transitions generate an intense pulsed current during shock compression. The latter is typically induced by gas guns or explosives. However, a detailed characterisation of the energy release processes triggered by the shock waves is difficult in such experiments, as they suffer from numerous problems such as electric breakdowns, leakage currents, the need for large samples which can only be used once, and the effect of thermal heating. Here, we propose to use dynamic diamond anvil cells (dDAC) and laser-induced shock waves for fast compression studies in order to understand energy conversion processes in ferroelectric and antiferroelectric materials with high power densities during pressure-induced phase transitions. In experiments with dDACs very high compression rates can be reached and very small µm-sized samples can repeatedly be used. Due to their high thermal conductivity, diamond anvils alleviate the heating of the samples during the compression processes and will allow us to separate the influence of pressure from that of temperature. Laser-induced shock waves can provide pressures up to several GPa for small µm-sized or larger samples and thus complement the dDAC studies.This energy release and pressure-dependent behaviour of the electric polarization during pressure-induced phase transitions in ferroelectric materials depends on several aspects, including type of the phase transition (ferroelectric or antiferroelectric), the character of phase transition (displacive or order-disorder) and the transition path (tetragonal-cubic or rhombohedral-cubic). We therefore propose to study BaTiO3- and BiFeO3-based ferroelectrics and Bi0.5Na0.5TiO3- based antiferroelectrics, in order to allow investigations of all these aspects.For the characterisation of samples, we will employ the second harmonic generation (SHG) method, electric measurements, Raman spectroscopy and x-ray diffraction. The SHG measurements will provide information on the character of the phase transitions and the pressure-induced behaviour of polarization and furthermore allow an evaluation of nanodomains or polar nanoregions in relaxor ferroelectrics. Methodological developments will allow novel SHG measurements of the polarization during fast compression in dDAC- and laser-induced shock wave experiments. The combination of in situ second harmonic generation and charge density measurements will help us to understand the interdependence between electric polarization, electronic conductivities, breakdown field and leakage current during the fast compression. Raman spectroscopy and x-ray diffraction will provide information on the local structure, long-range order and texture, and thus allow us to understand the correlation between structural modifications and polarization changes.

• DFG Programme: Research Grants