Public defence in Chemistry, M.Sc. (Tech) Kim Eklund

Title of the thesis: Pyroelectricity of ferroelectric perovskites investigated with quantum-chemical modelling methods

Thesis defender: Kim Eklund
Opponent: Dr. Chiara Gattinoni, King's College London, United Kingdom
Custos: Prof. Antti Karttunen, Aalto University School of Chemical Engineering

The consumption of electrical energy increases, for example due to artificial intelligence and data centres. In addition to minimizing consumption, it is necessary to consider the possibility of recovering energy converted to waste heat. There are several potential energy harvesting technologies available, yet energy harvesting at the device level remains technologically challenging. One possible method is the pyroelectric effect.

In the pyroelectric effect, temperature fluctuations cause a change in the polarization of the material. This can be recovered directly as electrical energy. The magnitude of the effect is determined by the pyroelectric coefficient. The utilization of the pyroelectric phenomenon is limited by materials that are not yet efficient enough for commercial applications, as well as the limited understanding of atomic-level phenomena. In addition, pyroelectric materials can be challenging from the perspective of sustainability, as the most efficient known pyroelectric materials contain lead.

Quantum-chemical modelling methods can be used to increase understanding of the atomic-level properties of materials. This can thus also aid in the development of new materials tailored for certain applications. The pyroelectric phenomenon has not previously been theoretically modelled on a large scale, especially for ferroelectric perovskite compounds. In these, the pyroelectric phenomenon is particularly strong. Measuring the pyroelectric coefficient experimentally is also challenging, giving additional reasons to develop accurate modelling methods.

As part of this doctoral thesis, a new quantum-chemical modelling methodology for pyroelectric compounds has been developed. It is applied to the calculation of the pyroelectric coefficients of three different perovskite compounds and two different perovskite solid solutions. The method used is based on density functional theory (DFT). In addition to the pyroelectric effect, other physical properties, such as thermal conductivity of the materials essential in device design, have been studied.

The results obtained in the thesis work are in line with previous experimental research data. The main finding is that the method has been validated for several different perovskite compounds, helping to understand the differences in their pyroelectric properties. This enables the further computational study and prediction of new lead-free pyroelectrics, optimized for applications in sustainable energy harvesting.

Keywords: pyroelectricity, perovskite, ferroelectricity, phonons, materials modelling, DFT

Thesis available for public display 7 days prior to the defence at Aaltodoc. 

Contact information: 
kim.eklund@aalto.fi