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UID:1655110800@ist.ac.at
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DESCRIPTION:Speaker: G. Jeffrey Snyder\nhosted by Maria Ibáñez\nAbstract:
  Zintl Phases as Thermoelectric Semiconductors G. Jeffrey Snyder Northwes
 tern Universitywww.thermoelectrics.matsci.northwestern.edu (http://www.the
 rmoelectrics.matsci.northwestern.edu) We often understand the physical pr
 operties of Zintl Phases by considering the perfect crystalline material t
 hat is defect free. Yet this perfect\, stoichiometric (valence balanced) c
 rystal is an intrinsic semiconductor with equal number of electrons and ho
 les. To make a n-type or p-type semiconductor we typically use point defec
 ts to introduce a slight valence imbalance that leads to excess electrons 
 or holes. Often intrinsic defects such as vacancies\, interstials or antis
 ite defects\, provide the necessary carriers to make the material a good t
 hermoelectric (e.g. Zn4Sb3\, Bi2Te3-Sb2Te3\, YbxCoSb3\, etc.). Most materi
 als\, however\, require extrinsic dopants to be a good thermoelectric and 
 intrinsic defects only make it more complicated. Sometimes intrinsic defec
 ts are so prevalent they are killer defects that prevent any dopant from m
 aking the material n-type or p-type.Point defects can also make gradual bu
 t profound changes to the band structure compared to the defect free compo
 und. This includes increasing band gap for higher temperature application\
 , reducing conductivity mass for higher mobility or band convergence for d
 ramatic increase in density of states (Pb(Se\,Te)\, Mg2(Si\,Sn)\, Bi2Te3-S
 b2Te3\,). In principle all of these defects can be better controlled by en
 gineering chemical potentials through phase boundaries. Even the Ni conten
 t MNiSn (M = Ti\, Zr\, Hf) Half-Heusler thermoelectrics can be sufficientl
 y altered to make substantial differences in electronic properties. The ex
 cess Ni produces impurity states in the band gap that changes the effectiv
 e band gap and leads to additional electron and phonon scattering. Refere
 nces[1] Zeier\, Snyder\, et al. Angew. Chem. Int. Ed. 55\, 6826 (2016)
LOCATION:Big Seminar Room B - Sunstone Building\, ISTA
ORGANIZER:
SUMMARY:G. Jeffrey Snyder: G. Jeffrey Snyder
URL:https://talks-calendar.ista.ac.at/events/3824
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