У оквиру семинара Центра за физику чврстог стања и нове материјале Института за физику у Београду, у уторак, 9. јула 2024. године у 13 часова у читаоници библиотеке „др Драган Поповић“ Института за физику, проф. Анте Билушић (Природословно-математички факултет, Свеучилиште у Сплиту) одржаће предавање:
Electrical and Thermal Transport in Complex Materials
САЖЕТАК:
Two currently active research topics are discussed: electrical transport in anatase and rutile, two mineral forms of titanium dioxide TiO2 and the investigation of the thermal conductivity of the proton exchange membrane of a hydrogen fuel cell. The polaron, which consists of a free electron and an accompanying phonon cloud, is a quasiparticle created by the electron-phonon interaction. It was first proposed to exist back in the 1930s and 1940s. Although polarons as a physical concept are already ninety years old, they and their effects on the physical properties of various systems are still being intensively investigated. They are categorised in terms of size into small polarons (with a size of the order of the lattice parameter) and large polarons (spread over many lattice sites). Anatase and rutile, two mineral forms of titanium dioxide TiO2, are examples of systems in which large (anatase) and small polaron excitations (rutile) occur. Our results on the temperature dependence of the electrical resistivity of rutile and anatase crystals at different magnetic fields show an activated behaviour between 5 K and 30 K, which is attributed to a polaron contribution. The magnetic field dependence of the activation energy increases linearly with the magnetic field, which can be explained by the discretisation of the electron energy into Landau levels and their dependence on the magnetic field. The low-temperature magnetoresistance data are in favour of an Efros–Shklovskii type line. Another aim of our research is to investigate and modulate the thermal conductivity of a proton exchange membrane (PEM) in order to improve the efficiency and longevity of hydrogen fuel cells. PEMs in polymer electrolyte fuel cells are ionomers that exhibit anisotropic thermal conductivity. It depends on the chemical composition, the degree of hydration and the size of the water domains, which are surrounded by polymer chains whose geometry is influenced by the stresses and strains caused by localised overheating in the membrane during operation. Frequency domain measurement methods (3ω method) with arbitrary sensor geometries enable the measurement of the general thermal conductivity tensor. In the inverted geometry of the 3ω method, we can determine the thermal conductivity of both the substrate and the polymer droplet above it.
The introductory part of the lecture will present the research and teaching opportunities in physics at the Faculty of Science of the University of Split.