Conversion between Magnetic, Electric, and Thermal energies in phase-transforming materials (COMET)

The aim of this project is to find new materials that can be used for conversion between different energy forms during structural phase transformations. This can potentially be used to harvest heat at low temperature with very high efficiency. A systematic search for such materials has begun, and several promising materials have been identified. A computer program has been developed to use relaxed structures from density functional calculations to predict which alloys satisfy the so-called cofactor conditions. These are requirements for crystal structures allowing for martensitic phase transformations with minimal dissipation of energy. This leads to very low hysteresis and the possibility of very many transformations without fatigue failure. Predictions from the program have been used to synthesize new compounds, and experimental work is now performed to verify the theoretical findings. At the same time, experimental methods are used for high-throughput screening of compounds in a similar search. Magnetron sputtering is used to make thin films with graded composition, so that many thousands of different compositions are produced simultaneously. These films have been investigated with several different experimental techniques, and several phase transitions have been identified. The final confirmation that this works is done by producing bulk samples exhibiting macroscopic phase transitions that can be precisely characterized by advanced microscopy, diffraction, spectroscopy, calorimetry and spectrometry.

Vi forventer at forskningsfeltet kan oppnå mange positive virkninger av resultatene fra Comet-prosjektet. Programvaren som er utviklet i prosjektet er allerede brukt i andre aktiviteter, og det er håp om at den også kan anvendes av brukere i andre institusjoner og fagfelt. Resultatene for tvillinger over mange skalaer i Pd-Cu-Sn-systemet er spennende og kan ha vidtrekkende konsekvenser for hele feltet av fasetransformerende materialer. Oppdagelsen av et nytt orienteringsforhold i martensittiske transformasjoner av en bestemt sammensetning er også overraskende, og kan føre til oppdagelsen av en ny klasse av fasetransformasjonsmaterialer med nye egenskaper. Prosjektresultatene kan også bidra til utvikling av svært effektiv høsting av lavtemperaturvarme. Dette kan ha en enorm innvirkning på energiforbruk, energieffektivitet og generelle bidrag til karbonutslipp og global oppvarming.

This project aims to develop a radically new technology for harvesting low-temperature heat. Such heat is available in huge amounts from renewable sources (e.g. geothermal and solar) as well as in many industrial and domestic processes. It is based on phase transformation materials (PTMs) exhibiting large and abrupt changes in a physical property at a certain temperature. The change can e.g. be structural, magnetic, or electrical, giving rise to shape memory alloys, thermomagnetic, and pyroelectric materials. These are physical phenomena that have been known for some time, but applications have been scarce due to severe problems with hysteresis and stability. However, recent progress in the theory of such transformations has in principle solved these issues, and the path is open to devices that can convert heat to electricity with efficiencies close to the thermodynamic limit (the Carnot efficiency). The COMET project will benefit from this development through collaboration with the groups that developed the theory. It will further develop and merge a whole suite of new techniques that are specifically aimed towards identifying novel PTMs with superior properties for energy harvesting. This includes the following advances at the frontier of this field: 1. The first true ab initio calculation of pyroelectric coefficients. 2. The first identification of a complete set of descriptors (defining parameters) targeted at PTMs. 3. The first high-throughput screening modelling study on PTMs based on first principles, exploiting the exceptional efficiency of the temperature-dependent effective potential method. 4. The first synthesis of compositionally graded films for high-throughput experimental search and validation of theoretically predicted PTM properties. 5. The first study linking first-principles calculations, synthesis, and characterization of microscopic and functional properties of multiferroic PTMs.