Materials for energy applications
Magnetic materials have an enormous impact in the energy sector as they play an important role in improving the performance of devices in electric power generation and conversion technologies (soft magnets), in electric motors and transportation technologies (hard magnets), in refrigeration technologies (magnetocaloric materials). Indeed, magnetic materials are essential components of motors, generators, transformers and actuators. Thus, the optimization of their properties is essential to face the continuous and unstoppable need of energy supply. Energy saving too has become a very importan issue in designing magnetic materials and their application in magnetoelectronic devices. With the progressive replacement of oil based fluids in trasportation by electric motors, the need of performant permanent magnets will increase more and more. The risk of supply and the high cost rare-earth (e.g. Nd, Sm, Pr) based and Pt and Pd based (FePt, CoPt L10 phase) magnets have stimulated computational and experimental investigations on novel and commercially attractive hard magnetic materials based on non-critical, easily accessible, stable and easily recyclable 3d metals like Fe, Co and Ni, with a high saturation magnetization and magnetic anisotropy suitable for ensuring a maximum energy product approaching, hopefully surpassing, that of RE-based PMs.
2a) Magnetocaloric materials: "Erasteel materials”
The magnetic cooling is a new promising technology in refrigeration systems. It has many advantages when compared to the standard gas compression technology, such as a decrease of energy consumption and reduction of the acoustic and environmental pollution. The magnetic cooling is based on Magnetocaloric effect (EMC). Research on magnetocaloric materials has made a far step ahead with the discovery of the giant magneto caloric effect (GMCE) by Gschneider and Percharsky in 1996. Recently, Erasteel developed components with a giant magnetocaloric effect using powder metallurgy. This development includes the synthesis of magnetocaloric alloys powders by gas atomization method tand heir functionalization in order to fulfill the requirements of magnetic refrigeration systems.
In our work we are looking for materials which can be applied in the industry. We will be in charge of the synthesis of magnetocaloric materials, with transition temperature near room temperature, and erasteel materials especially doped La (Fe, Si) 13 using the arc melting technique and other methods of preparation (ball milling, autocombustion). We will optimize the structural and magnetic properties of these alloys substituting the rare earth and the transition metal by other elements. We will test our samples and make them useful for magnetic refrigération.
Aims and methodology
Our objective is to synthesise magnetic materials with Curie temperature near room temperature and with large magnetocaloric effects. We will choose as principle material La(Fex Si 1−x )13 where its Curie temperature is far from RT. We will try to enhance its Curie temperature and improve the refrigeration capacities. We will try to make this material useful in the industry and will test it using an innovative magnetic cooling machine. Conventional experimental techniques (magnetometry, Xray diffraction, calorimetry, Mössbauer....) will be used to characterize our samples.
Method of preparation and structural analysis:
Firstly, our samples will be prepared using different methods of preparation (Arc melting, Ball milling , autocombustion). Then we will analyse their structure using X-ray diffraction. Microstructure will be investigated using scanning electon microscopy and scanning tunneling microscope .
We will perfom magnetic meausurements under low applied magnetic field to determine the Curie temperature. Magnetization as fuction of applied field will be measured at different temperatures. Then we will calculate the entropy change indirectly from it. Direct measurements of the temperature change around room temperature will be also performed.
The design and the building of the work will be motivated by the following criteria:
1. Simultaneous measurements of the magnetocaloric effect as well as of the transition temperature of different magnetocaloric materials.
2. Evaluation of the forces acting on the materials and the study of different phenomena related to their internal state, like hysteresis and demagnetization effect, etc.
3. Properties determined close to and at room temperature.
4. The measurements must be performed in real conditions that are encountered in a magnetic refrigeration system in a practical application.
2b) Magnetocaloric materials: Ni-Mn-Ga Heusler alloys
( Team leader: Valeria Rodionova)
The activity will be devoted to the search of new materials for eco-friemdly magneto-refrigeration technology (magnetocalorics) and energy saving. In this context a project is devoted to the “Control of structural and magnetic properties by internal stresses in Ni-Mn-Ga based Heusler alloys in form of magnetic microwires and thin films in view of applications in energy saving. Magnetic Heusler alloys are multifunctional materials where the magnetic and structural order are closely connected. The co-occurring of structural and magnetic phase transitions leads to a variety of effects: magnetic field induced strain (MFIS), giant magnetocaloric effect (MCE) and giant magnetoresistance (GMR). Key factors for MFIS, i.e. promising for energy harvesting devices, are high magnetocrystalline anisotropy, high saturation magnetization and modulated crystal structure. To achieve the largest values of these parameters for materials with different forms and sizes (glass-coated microwires, thin films) the understanding of how structural and magnetic properties correlate with a change of form and size is required. When the first attempts of obtaining and studying of thin films and microwires were made, it became clear that optimal chemical composition of the Heusler alloys for the bulk materials is not optimal for the Heusler alloys in the form of a thin film or microwire. One of the reasons of such discrepancy is the influence of internal stresses (because of glass coating in microwire, substrate in thin films) on the above objects. The dependence of structural and magnetic properties on applied stresses is well studied for Ni-Mn-Ga bulk Heusler alloys, but such behavior is more complex for thin films and microwires and still remains at rudimentary level. The objective of this work is to establish the relationship between structural and magnetic properties in Ni-Mn-Ga Heusler alloys with different forms (bulk materials, microwires, thin films), to find out how internal stresses affect these properties, to explain the mechanism of influence and to find a way how to control the properties through the changes of stresses. Thin films of Heusler alloys will be grown by pulsed laser deposition technique and characterized in collaboration with Dr. Alexander Goikhman (IKBFU). The Current project is conducted in collaboration with the groups of Prof. Vladimir Khovaylo, National Institute of Science and Technology MISiS, Moscow, Russia; Prof. Miki Hiroyuki, Tohoku University, Sendai, Japan; Dr. Rastislav Varga, Institute of Physics of Pavol Jozef Šafárik University, Kosice, Slovakia; Prof. Arcady Zhukov, University of a Basque Country, San Sebastian, Spain
2c) Transition metal oxide (TMO) based nanostructures for use as the electrode material in supercapacitors.
(Ashutosh Kumar Singh)
Transition metal oxide (TMO) based nanostructures will be prepared and investigated for their use as the electrode material in supercapacitors. As the pseudo-capacitative performance is mainly governed by the surface or near surface faradic reactions, the decrease of the size of the electrode material will increase the effective surface to volume ratio and thereby the active material use. Designing of some special nanostructure with higher effective surface area will be very useful in obtaining higher capacitative performance in terms of higher specific capacitance, high energy and power density. TMOs, especially NiO, CoO etc., have been chosen because of their higher theoretical specific capacitance, higher electrochemical and thermal stability, easy availability and low production cost. Higher conductivity of the electrode material is highly desirable for free flow of electrons to the current collectors. So, we can use carbon based materials for this purpose. Also, higher conductivity can be achieved by hydrogenation or nitrogenation or via doping of the oxide materials. This will incorporate electrons or holes within the system depending on the type of the semiconducting material.
Photo electrochemical Cell : Using these metal oxide based nanostructures we can fabricate the photo electrochemical cells, which have broad application in oxygen and hydrogen generation by oxygen evolution reactions (OER) and hydrogen evolution reactions (HER), respectively.
Design and Fabrication of Nanophotovoltaics & Nanoelectronics Devices with novel functionality: by combining suitable p-type and n-type semiconducting oxide materials, we will fabricate junction diodes for practical electronic and opto-electronic applications. In this p-n junction nanowires additional charge separation can be produced by exciting the materials with light and also with current. First procedure will lead to the fabrication of photovoltaic devices.
In case of nanowires, the transport properties will be investigasted, especially the electronic conductivity of single nanowire by making the current contacts using nano-lithography. Sharp edged nanostructures of semiconductors readily emit electrons at relatively lower voltages than other nanostructures because of their high electron density at the tip. So, study of the field emission properties of nanowires, nanospikes, nano-urchin type nanostructures will be very interesting for their possible applications in display devices replacing the traditional LCDs.
2d) New Silicon and Germanium based thin film and bulk structures for thermoelectric and magnetosensoric applications.
(Team leader: Alexander Goikhman)
Main goals of the project are:
- ab-initio calculation, modeling and measurement of the bulk and thin film Si and Ge based structures for thermoelectric and magnetosensoric applications;
- development, growth and in situ characterization of the complex epitaxial Si and Ge based intermetallics with perpendicular magnetization, identification of new metastable phases;
- development of the resonance methodics for maсro, micro and nano properties characterization of such materials.The project will be done with the main partners: Kirensky Institute of Physics (Russian Academy of Sciences, Siberian Branch) where the magnetic characterization would be acquired, Deutsche Electron Synchrotron (DESY) in Hamburg and European Synchrotron Radiation Facility in Grenoble, where we are going to develop new setups for in situ growth and characterization for proposed materials by synchrotron x-ray diffraction, nuclear resonance scattering etc.