2018 - Sustainable Industrial Processing Summit & Exhibition
4-7 November 2018, Rio Othon Palace, Rio De Janeiro, Brazil
Seven Nobel Laureates have already confirmed their attendance: Prof. Dan Shechtman, Prof. Sir Fraser Stoddart, Prof. Andre Geim, Prof. Thomas Steitz, Prof. Ada Yonath, Prof. Kurt Wüthrich and Prof. Ferid Murad. More than 400 Abstracts Submitted from about 60 Countries.
Abstract Submission
Login

DETAILLED PROGRAM OVERVIEW

Back
    Spinodal Decomposition in High-Entropy Half-Heusler Thermoelectrics with High ZT~1.5
    Peter Rogl1;
    1UNIVERSITY OF VIENNA, FACULTY OF CHEMISTRY, Wien, Austria;
    PAPER: 189/SISAM/Keynote (Oral)
    SCHEDULED: 14:00/Wed./Copacabana A (150/1st)



    ABSTRACT:
    Besides skutterudites and Zintl phases, Half Heusler (HH) alloys are currently the most promising candidates for thermoelectric (TE) devices at elevated temperatures; they can be used in a wide range of temperatures, and their starting materials are abundant and cheap [1]. In particular, the nanostructuring of TiNiSn-based thermoelectric materials - not only by ball-milling but also by preferably system-inherent phase separation - has accomplished multicomponent HH alloys with attractive ZTs for n-type TE materials based on (Ti,Zr)-Ni-Sn. These values could be achieved on the basis of a profound knowledge not only on isothermal phase relations, temperature dependent solubilities, but also on solidification behavior. The detailed experimental investigation of the constitution of the (Ti,Zr)-Ni-Sn systems, including liquidus projections, Scheil solidification diagrams, as well as CALPHAD modelling, provided the necessary basis for an elaborate synthesis (annealing/hot-pressing) route in order to get a suitable and reproducible microstructure. In addition, exploiting inherent but coherent binodal/spinodal demixing at subsolidus temperatures within the sections TiNiSn-ZrNiSn and TiNiSn-HfNiSn, we were able to achieve for the n-type half Heusler alloy Ti0.5Zr0.25Hf0.25NiSn a ZTmax = 1.5 at 825 K. The demixing is a balanced effect of destabilisation of the solid solution by a positive enthaphy of mixing, compensated by elastic strain energy (coherent binodal) but also by the entropy of mixing. In this respect, the five component thermoelectric material can be considered as a so-called pseudoternary high-entropy alloy system. The experimental data are backed by SEM/TEM analyses as well as by DFT results.

    References:
    [1] G. Schierning, R. Chavez, R, Schmechel, B. Balke, G. Rogl, P. Rogl, "Concepts for Medium-high to High Temperature Thermoelectric Heat-to-Electricity Conversion: A Review of Selected Materials and Basic Considerations of Module Design", Translational Materials Research 2, 025001, 1-26 (2015)