4 / 9
allied
academies
Page 32
May 20-21, 2019 | Vienna, Austria
Biomaterials and Nanomaterials &
Materials Physics and Materials Science
2
nd
International Conference on
Journal of Materials Science and Nanotechnology | Volume 3
CALPHAD-assisted synthesis of Hf-free Half Heusler thermoelectrics with high ZT ~ 1.2
Peter Franz Rogl
1,2
, MGürth
1
, P Sauerschnig
1
, J Vrestal
4
, V Romaka
5
, A Grytsiv
1,2,3
, G Rogl
1,2,3
, K Yubuta
6
,
and
E Bauer
2,3
1
University of Vienna, Austria
2
Christian Doppler Laboratory for Thermoelectricity, Austria
3
Institute of Solid-State Physics, Austria
4
Masaryk University, CR
5
Lviv Polytechnic National University, Ukraine
6
Tohoku University, Japan
B
esides the well-known skutterudites and Zintl phases,
Half Heusler (HH) alloys currently are the most
promising candidates for thermoelectric (TE) devices
at elevated temperatures: they can be used in a wide
temperature range and their startingmaterials are abundant
and cheap. Particularly via nano structuring of TiNiSn-
based thermoelectric materials by top-down (ball milling)
and bottom-up (spinodal decomposition/precipitation)
mechanisms. We have accomplished multicomponent HH
alloys with attractive ZTs for n-type TE materials based
on (Ti, Zr)-Ni-Sn. These values were achieved on the basis
of a profound knowledge not only of isothermal phase
relations, temperature dependent solubilities but also of the
solidification/annealing behavior.
The detailed experimental investigation of the constitution
of both relevant systems Ti-Ni-Sn, Zr-Ni-Sn as well as (Ti, Zr)
NiSn - (Ti,Zr)Ni2Sn including liquidus projections and Scheil
solidification diagrams, as well as CALPHAD modelling,
provided the necessary basis for an elaborate synthesis
(annealing/hot-pressing) route in order to reproducibly
get a suitable microstructure. Exploiting furthermore the
system inherent but coherent binodal/spinodal demixing
and precipitation at sub solidus temperatures within the
sections TiNiSn-ZrNiSn and (Ti
0.5
Zr
0.5
) Ni1+xSn we were able
to achieve for the n-type half Heusler alloy a ZTmax = 1.2 at
825 K. The demixing is a balanced effect of (i) destabilization
of the solid solution by a positive enthalpy of mixing
compensated by elastic strain energy (coherent binodal) but
also (ii) by the stabilizing effect of the entropy of mixing. The
experimental data are backed by SEM/TEM analyses as well
as by DFT results.
Speaker Biography
Peter Franz Rogl has completed his PhD at the age of 25 years from
University of Vienna, Austria. He is full professor of physical chemistry of
materials at University of Vienna, Austria. He has over 700 publications.
His publication H-index is 49 and he has been serving as an editorial
board member of reputed Journals.
e:
peter.franz.rogl@univie.ac.atNotes: