RESEARCH
The research of our group encompasses a variety of research fields associated with the fundamental and applied investigations of the new materials, and include complementary experimental and theoretical approach.
Experimental research is mainly focused on hyperfine interactions, which have been subject of investigations in this group for a long time within TDPAC, and recently Mössbauer spectroscopy. These experiments are used in a research of the structural and dynamic properties of the intermetallic and the semiconductor samples on the atomic scale. Complementary to this, fundamental research of several viable applications have also emerged, particularly in the field of new materials for renewable energy application (hydrogen storage and hydrogen production)
A detailed theoretical study of the structure, electronic properties and the hyperfine interactions parameters is performed using DFT and molecular dynamics codes.
In the past century mankind has become accustomed to enjoy the benefits of constantly available energy sources, but in the past few decades mankind has also became aware of the fact that this situation will not last forever. Besides the fact that the fossil fuels are becoming less and less available, they also contribute, great deal, to the destruction of nature. Therefore, it has become very well known that energy sources based on the fossil fuels must be replaced, or at least supplemented with alternatives. As a consequence, extensive research is conducted to find the alternative power sources, and to avoid any undesirable side effects present in fossil fuels.
Hydrogen-based sources are, among others, recognized as promising, renewable, future sources of energy. Nevertheless, limiting factor for the exploitation of hydrogen as a fuel is related to the difficulty of its storage. Recently, many experimental and theoretical investigations were conducted to understand the process of storing hydrogen in metals and intermetallics, especially to study structural, thermodynamical and kinetical factors of hydride formation. Besides these macroscopic aspects it is also of great importance to study the microscopic properties of promising storage materials. Therefore, to understand the overall process of hydrogen storage, and to improve the storage capacities, reversibility of absorption-desorption cycles, or reaction kinetics, many investigations are still conducted from the fundamental point of view.
To widen the knowledge that we have on the interaction of hydrogen with structure, and its behaviour within the material, nuclear-based methods can be of great importance in the investigation and characterization of possible hydrogen storage materials. It should be amplified that combination of various methods plays an important role in many ongoing activities.
In our group we have two nuclear-based methods Time Differential Perturbed Angular Correlation (TDPAC) and Mossbauer spectroscopy. Both methods use hyperfine interactions to obtain information on the microstructure of solids. PAC method is based on the detection of spatially anisotropic gamma rays, which are emitted from radioactive probe atoms, while Mossbauer spectroscopy is based upon the resonant apsorption and emission of gamma rays by Fe ions. Unlike Mossbauer and Nuclear Magnetic Resonance (NMR), which detect nuclear energy level splitting that occurred as a consequence of interaction of nuclear moments with its surrounding field, PAC methods measure time dependence of gamma ray emission pattern. Another speciality of this method is that atomic probes used are 181Hf and 111In. They exhibit radioactive decay into 181Ta and 1a1Cd, which are then considered to be impurities, located somewhere in the crystal lattice.
Nuclear methods are very sensitive to any changes in electronic structure, and they can easily be recorded. Nevertheless, if we know that something has happened to our system, but we can’t explain what, or even utilise that knowledge for future, one is free to say that that knowledge is limited, and to a certain point useless. Therefore, it is important to interpret the results equally qualitatively and quantitatively, and even more important is the future usability of new knowledge! To be able to do that, combination of advanced modeling, various synthesis methods and various characterization tools is therefore essential.
Because computational investigations are only limited by the available computational sources and the imagination of a scientist, possibilities for calculations are, in general, endless. If one wants to study one particular property, one just has to know how to set up the starting system, and to manipulate it. From there possibilities are endless.
Even though most scientific research conducted these days is focused on obtaining only practical solutions, fundamental research is equally, extremely important, because, in time, appropriate fundamental research leads to an appropriate application.
Parameter that is easily calculated and obtained from various nuclear methods is, for example electric field gradient (EFG), or asymmetry parameter. Microscopic properties of materials can be studied in details when this parameter is obtained with appropriate computer software. In our group, for the calculation and analysis of hyperfine interaction parameters in solid state materials we use Wien2k. EFG directly depends on the charge distribution around observed nucleus, nearest neighbor distance and their distribution. That is why investigation of electron density from Wien2k can lead to knowledge of desired physical properties.