Seminarium Oddziału Badań Magnetyków
Microsoft Teams
An approach towards Zero Thermal Expansion
dr Shovan Dan
Oddział Badań Magnetyków, INTiBS PAN
Seminarium odbędzie się zdalnie w aplikacji Microsoft Teams. W celu wzięcia udziału w wydarzeniu należy dołączyć do zespołu Seminarium OBM.Można do niego dołączyć na stałe przy użyciu kodu dostępu ol7omod (dotyczy to osób posiadających konto w domenie intibs.pl, pozostałe osoby proszę o kontakt z prof. dr. hab.Adamem Pikulem, prof. INTiBS PAN ())
Streszczenie:
In general, most of the materials expand with increasing temperature due to anharmonic nature of lattice vibrations. However, there exist a few materials exhibiting the rare phenomenon of volume contraction on heating. These are usually called negative thermal expansion (NTE) materials. The even rarer phenomenon of zero thermal expansion (ZTE), i.e., a material that neither expands nor shrinks with temperature, have also been found. Technologically, ZTE materials have immense potential in application-oriented research. In many cases, ZTE is achieved in a composite material by appropriately combining an NTE material with another one that exhibits regular, positive thermal expansion. This, however, often undergoes thermal stability problem due to the nature of such inhomogeneous solid solutions. ZTE could also be achieved by tweaking an NTE material where the strengths of NTE are reduced gradually.
The present presentation is focused on the development of such ZTE materials. To fulfill our purpose, we worked on a well-known intermetallic series R2Fe17 (R= rare earth metals) and PbTiO3 based ceramic compounds, which show NTE below their respective Curie temperature. We understood the mechanism of NTE on those material in a very intuitive way, and decided to gradually weaken the origin of NTE by selective elemental substitution. For a certain critical concentration, the materials show ZTE over a vast temperature window. Ho2Fe16Cr is such a compound that shows almost zero expansion from very low temperatures to a temperature well above room temperature (RT). A few ceramic compounds will also be discussed that show ZTE in a very large temperature region RT ± 150 K. For the estimation of thermal expansion, we had to calculate the volumes of unit-cell at different temperatures using a temperature-dependent x-ray diffractometer.
At the end, if you permit, I will tour the other avenues of research (e.g., on search of new permanent magnets, magnetocaloric material, magnetic critical analysis near phase transition, skyrmions, etc.) that I have explored within the scope of my PhD work.
