Thermoelectric materials
Thermoelectric magnetic sulfides
The project explores novel thermoelectric materials for the conversion of the waste heat to electric energy. Considering the price, processing and potential toxicity we will focus on optimization the thermoelectric behaviour of sulfide ternary systems based on copper, iron and chromium. As high absolute value of thermoelectric coefficient, low electrical resistance and low thermal conductivity are prerequisites of effective thermoelectric conversion, the interplay between magnetic interactions, crystal structure and thermoelectric response due to the constitutive role of magnetic metals will be studied. As optimization routes towards better materials both chemical doping and nanostructuring will be used, starting from pristine materials in single crystalline form. In addition to chemical, morphological and thermoelectric properties the materials will also be examined in high magnetic field and using special techniques, including high pressures and Mössbauer spectroscopy. Experiment will be supplemented by theoretical calculations of electronic structure and transport coefficients.
- Prague - Growth Pole of the Czech Republic (2018-2020).
The aim of the project is to develop innovative equipment that will help to exploit the energy losses in the management of primary energy sources and the subsequent commercialization of specific technologies, which will increase the efficiency of waste heat management. Waste heat currently accounts for about 60% of all energy consumed. From this amount of energy, about 5-8% can be converted to electricity by thermoelectric conversion. The technology of thermoelectric conversion has long been known, but has recently significantly increased its efficiency through the research of new materials and its efficiency can be expected to increase further. The intended output is therefore the lower energy demand of technological equipment, which produces a significant amount of waste heat. These activities will be implemented in particular in segments where the expected technologies can be effectively deployed, such as transport, building management and waste disposal. In particular, we plan a detailed mapping of energy inputs, operating temperatures, heat flows and potentials, and hence possible thermal leakage in the relevant technologies, which can be divided into three basic segments:
- Mobile waste heat sources (technology based on modern combustion power aggregates of urban and suburban buses).
- Low-potential sources (this technology is characterized by low temperature gradients, but with the possibility of overall high energy heat flows, such as large data centers and server rooms).
- High-potential sources (this technology is characterized by high temperatures and high heat flows. These are stationary sources serving either directly or indirectly for the production of heat where technologies are based on modern high-temperature combustion with high efficiency, such as waste incineration plants).
For a modern gasoline engine it is only about one third of the energy (for diesel engines this is about 40%) contained in fuel which is converted into mechanical work required to move the vehicle. Unused energy escapes into the environment in the form of hot exhaust gases, hot air, or thermal energy emitted from the surface of hot engine parts and accessories. The proposed project seeks to design a complex system for unused heat utilization, leading to increased engine efficiency and thus also reduction in the concentration of undesirable greenhouse gases. It is a combination of direct heat recovery (e.g. we use the heat from the exhaust gases to faster warm the engine and the interior after starting the engine) and the indirect “thermoelectric conversion of heat energy” recovery method, where the engine is already sufficiently warmed-up and thus we can use the heat from the exhaust gases to generate electricity to run electrical devices in the car.
The project is directed to a new class of intercalation systems Ln(x)CoO2 (Ln=La,Y,rare-earth), prepared by an ionic exchange from the isostructural sodium cobaltate. Their structure is based on hexagonal layers of the edge-sharing CoO6 octahedra that alternate along the c-axis with layers of lanthanide ions. Through the variable content of Ln3+ (x<1/3), an electronic behavior of the cobalt subsystem, in particular the conduction and thermopower, is effectively controlled. Our aim is to optimize the technology of the ionic-exchange using the rare-earth nitrates or halides, to vary the mixed valency Co3+/Co4+ by deintercalation or alkali-earth substitution, and to explore systematically the structural, magnetic and electric properties of the products. For a theoretical analysis, the ab-initio and effective Hamiltonian calculations will be undertaken. It is expected that the insertion of magnetic rare-earths will make the electric transport sensitive to external magnetic field.
Direct thermal to electric power generation represents a very prospective method for recovery of the high temperature waste heat. In this context the development of chemically stable and efficient thermoelectric ceramics, composed of nontoxic and price affordable elements, has a key role for extensive application of thermoelectric materials. The project is thus aims to investigate and characterize oxide materials, which form efficient thermoelectric unicouple. The targeted materials are principally derived from layered oxide cobaltates (as p-type legs) and Mn-based perovskites or ZnO (as n-type legs). Apart of the standard thermoelectric requirements for relevant materials, namely the low thermal conductivity, the special care will be focused, given the intense thermal strain and oxidation-reduction conditions at high temperatures, on the functionalization of thermal and electrical interfaces. In this respect we plan to utilize conducting oxide nanotubes, which are able to release mechanical stresses.
The project deals with a fundamental research on novel oxide thermoelectric materials of p-type considered for the electric power generation using waste heat. As concerns the conversion efficiency of such thermoelectric generators, the materials should operate in wide temperature range and keep at the same time a high figure of merit, ZT =(S
2R)T, where S is the Seebeck coefficient, R is the ratio of electric resistivity and thermal conductivity and T is the actual temperature of the thermoelectric segment. In this respect, some cobalt oxides have been found promising, especially thanks to the pioneering work of Terasaki on thermoelectric properties of Na
0.6CoO
2 in 1997. The present project is focused on material research of a broad class of complex cobaltites, based both on the hexagonal and tetragonal arrangements of the thermoelectrically active CoO
2 layers. The properties of the cobaltites will be optimized by an improvement of their intrinsic properties through modification of the chemical composition, as well as by a control of morphology and microstructure of the prepared materials.
