Nanocharacterisation of TiNiSn Heusler alloys for thermoelectric applications

Dr Donald MacLaren, School of Physics and Astronomy, University of Glasgow. Part of the condensed matter group research seminar series. All are welcome to attend.

Thermoelectric generators (TEGs) can be used to 'scavenge' otherwise wasted heat to produce cheap electricity. Heusler alloys have attracted much attention as potential TEG materials as they are composed of cheap, non-toxic materials and have been demonstrated to have modest TEG performance. The most efficient thermoelectric Heusler overcome a performance-limiting thermal conductivity through the incorporation of nanostructures that scatter phonons and thereby interrupt thermal transport. However, nanostructures such as full-Heusler inclusions need to be thermally stable if they are to operate under high-temperature environments for prolonged times. In many cases, the thermodynamics of these kinetically-limited structures have not been studied in detail.

Indeed, although functional Heuslers are of broader interest to the condensed matter community, information on phase segregation and its impact on performance is limited. I will discuss the nano-characterisation of Cu-doped TiNiSn Heusler alloys, using a battery of techniques to determine the nature of phase segregation and nanostructuring arising in this particularly promising n-type TEG. Chemical analysis reveals remarkably inhomogeneous structuring, ranging from grain-by-grain micron-scale variations right down to atomic-scale fluctutions in crystallographic site occupancy. I will then turn to recent thin film studies and show that pulsed laser deposition can be used to deposit epitaxial thin TiNiSn films, albeit with a degree of spontaneous phase segregation.

The ideal deposition conditions will be discussed; absolute quantification of the stoichiometry using electron energy loss spectroscopy will be outlined; and annealing experiments in-situ to the electron microscope will be shown to reveal potentially beneficial aspects of spontaneous nanostructuring.

For more information, please contact Dr Satoshi Sasaki (