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Introduction/Purpose
Reversible diffusionless first-order phase transformations are a fundamental part of phase change materials and shape memory alloys
[1]. Some of
these materials even possess useful physical characteristics that show abrupt changes e.g. in their electrical[2] and magnetic
[3] polarizations. These phase transformations can be studied using multiple techniques, enabling access to different types of information including length scales and time periods, but how should this characterisation be approached? Methods TEM studies give highly relevant data in this field of research, from detailed crystallographic structures, to relative orientations between grains and
phases and to the phase transformation temperature. However, TEM analyses are time consuming and requires small sample sizes and ad hoc preparation. High-throughput measurement techniques are thus required in the search for improved compositions and new materials in order to
rapidly assess the properties of many samples or samples with graded composition
[4]. Optical methods (for example unpolarised and polarised microscopy and thermal imaging) and electric conductivity measurements can for example be used to map phase transformation temperatures much faster and on much larger areas than traditional TEM techniques. XRD and SEM-EDS-EBSD can then be applied to obtain initial
crystallographic and microstructure information on an intermediate size scale, before TEM is applied for the in-depth study of the most relevant
compositions. Results We applied this multi-pronged approach in the search for Heusler and half-Heusler alloys with a low temperature martensitic phase transformation
and with low thermal hysteresis, with potential applications in waste heat energy harvesting.
Conclusions Drawing advantage of the strengths of multiple analysis techniques – with respect to the obtainable information, the sample size and/or the time
frame of the analyses – renders the search for new phase change materials more effective. It enables faster identification of potential target
compositions and of sample areas optimal for in depth studies.
Selected references
[1] David Dye, Nature Materials14 (8), 760 (2015).
[2] M. M. Vopson, Critical Reviews in Solid State and Materials Sciences40 (4), 223 (2015).
[3] L. Huang, D. Y. Cong, L. Ma, Z. H. Nie, Z. L. Wang, H. L. Suo, Y. Ren, and Y. D. Wang, Applied Physics Letters108 (3) (2016).
[4] M. L. Green, C. L. Choi, J. R. Hattrick-Simpers, A. M. Joshi, I. Takeuchi, S. C. Barron, E. Campo, T. Chiang, S. Empedocles, J. M. Gregoire, A. G. Kusne, J. Martin, A. Mehta, K. Persson, Z. Trautt, J. Van Duren, and A.
Zakutayev, Applied Physics Reviews 4 (1), 011105 (2017).
