Michael Zehetbauer

Abstract

Improving the efficiency of functional materials through targeted SPD-induced structural heterogenisation

SPD processing has demonstrated significant increases in efficiency with regard to functional properties. These include e.g. hydrogen storage in solid metals and alloys, where the focus is not only on maximising the storage capacity but also on the long-term storage stability of the solid. The formation of thermally stable vacancy-type nuclei for heterogeneous hydride formation plays a central role in this process [1]. Of particular interest are RT hydrogen storage materials such as FeTi and FeTi-based high-entropy alloys (HEAs). Recently, SPD processing assisted by a sacrificial phase was applied to obtain porous hydride–polymer FeTi HEA & polymer composites, which provide easy activatability, enhanced storage kinetics, and mechanical stability [2]. 

Other functional materials comprise SPD processed thermoelectrics where world-record values of thermoelectric efficiency ZT were reached for n- and p-type skutterudites. Recently, a thorough analysis of SPD-induced lattice defects [3] showed that the successive integration of vacancies into cell boundary dislocations triggers the formation of regular subgrain walls [4]. These significantly increase the phonon-scattering efficiency and thus decrease the thermal phonon conductivity, thus leading to a rise of ZT. However, too large defect densities lead to a marked increase in electrical resistivity, which may be no longer compensated by the slight decrease of thermal conductivity. A similar effect is found in Half-Heusler [4] and clathrate thermoelectrics which exhibit increased semiconductor behavior and thus a markedly enhanced specific defect resistivity. 

Part of this work was carried out in frame of project HEAfine4H2 of the Austrian Research Promotion Agency (FFG), grant 914968 

[1] P. Cengeri, Z. Abbasi, Y. Kimoto, Y. Morisada, H. Fujii, N. Enzinger, Ch. Sommitsch, G. Krexner, M.J. Zehetbauer, E. Schafler, J. Mater.Sci. 59, 5906–5922 (2024) 

[2] L. Schweiger, F. Spieckermann, P. Cengeri, A. Schökel, M. Zehetbauer, E. Schafler, D.Kiener, J.Eckert; Adv. Sci. 2025, e07168 (2025) 

[3] G. Rogl, V. Buršíková, V. Romaka, P. Cengeri, J. Buršík, E. Schafler, M. Zehetbauer, P. Rogl, Acta mater. 296, 121290 (2025) 

[4] G. Rogl, V. Bursikova, K. Yubuta, H. Murayama, K. Sato, W Yamamoto, A. Yashuhara, P. Rogl, J.Alloys Comp. 977, 173431 (2024)