[institut] Center for Solid State Physics and New Materials seminar, Tuesday, July 9th

[Nenad Lazarevic]

Dear Colleagues,

You are cordially invited to the Center for Solid State Physics and New 
Materials seminar, which will be held on Tuesday, July 9th, 2024, at 
13:00, in the library reading room "Dr. Dragan Popović" of the Institute 
of Physics Belgrade.

The talk, entitled "Electrical and Thermal Transport in Complex 
Materials," will be given by Prof. Ante Bilušić from the University of 
Split, Faculty of Science.


Abstract:
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.

Best regards,
Nenad Lazarevic
-- 
Center for Solid State Physics and New Materials,
Institute of Physics Belgrade
Pregrevica 118, 11080 Belgrade, Serbia
http://www.ipb.ac.rs/