21.10.2021 - 12:15
On 21 October at 12:15 Evgenii Strugovshchikov will defend his doctoral thesis “First-principles studies on rare-earth metal-hydride-based smart materials” for obtaining the degree of Doctor of Philosophy (in Materials Science).
Dr. Aleksandr Pishtsev, University of Tartu
Prof. Dr. Smagul Karazhanov, Institute for Energy Technology (Norway)
Prof. Dr. Peter Kratzer, University of Duisburg-Essen (Germany)
Dr. Habil. Phys. Juris Purans, University of Latvia (Latvia)
There is currently a high demand for functional materials that can serve as the basis for the development of new energy-efficient devices and mechanisms with a wide range of applications, capable of operating under various Earth and space conditions. As the first results have shown, rare-earth metal oxyhydrides offer a number of useful functionalities that can be directly utilized in modern technological applications, especially in the design of high-performance optical and electromechanical devices. Chemical engineering of rare-earth metal oxyhydrides has begun more than 10 years ago when it was discovered that the addition of oxygen into the hydride structure not only rearranges the stoichiometry due to the flexible stabilization of hydrogen and oxygen positions in the crystal lattice, but also greatly expands the set of characteristics of the modified metal-hydride system. This has opened up great opportunities to improve a number of key properties of metal hydrides and enhance their functionality, thus enabling researchers to flexibly modify and improve their optical, mechanical, and electronic properties.
From a scientific and technological point of view, understanding what functional role the chemical addition of oxygen plays in the properties of solid oxyhydrides is the most important problem. Thus, the main goal of the present PhD thesis was to significantly extend our knowledge about the behavior of oxygen in rare-earth metal hydrides. Using modern methods of mathematics, theoretical physics and crystal chemistry, as well as extensive numerical calculations on a supercomputer, we investigated the most probable structural and compositional configurations in rare-earth metal oxyhydride systems. This allowed us to predict a large number of compounds with different crystal structures and oxygen/hydrogen ratios and construct a ternary phase diagramm for Y-H-O variables. We have characterized the key role of oxygen in the formation of new materials, which guides crystallization into a stable oxyhydride structure. Among all ternary oxyhydride compositions, we found that certain oxyhydrides can be stabilized in polar noncentrosymmetric phases that have outstanding elastic, piezoelectric, and electromechanical characteristics. One of these phases corresponds to a special tetragonal structure whose lattice configuration is characterized by a unique chiral structural organization encompassing all cations and anions in the unit cell. Based on the calculated electronic and optical properties, we also proposed two different prototypes of optical coatings in which oxyhydride thin films play a key role: (i) a low-emissivity coating model and (ii) a light-absorbing non-reflective coating model.
The results of our research have significantly enriched the knowledge base on the material properties of rare-earth metal oxyhydrides. They revealed details of the microscopic nature of the electronic, elastic, electrical, and optical properties of these materials. This allowed us to understand how their properties and functional characteristics could be driven by various chemical and physical factors. In addition, we proposed possible scenarios for the prediction and design of oxyhydride materials with promising functions, which can be further used in the development of modern optical and electromechanical devices.
W. Ostwaldi 1, aud B103