posted on 2020-09-04, 12:36authored byZhiran Wang, Hong Wu, Ming Xi, Huaxing Zhu, Lu Dai, Qihong Xiong, Guiwen Wang, Guang Han, Xu Lu, Xiaoyuan Zhou, Guoyu Wang
GeSe
was theoretically predicted to have thermoelectric (TE) performance
as high as SnSe. However, the relatively high TE performance was not
achieved experimentally in doped GeSe samples with an original orthorhombic
structure but observed in Ag(Sb,Bi)(Se,Te)2 alloyed samples
that crystalize in either a rhombohedral or cubic structure. Herein,
to clarify the crystal structure-dependent properties, the electrical
and thermal transport properties of GeSe1–xTex (0 ≤ x ≤ 0.5), where orthorhombic, hexagonal, and rhombohedral phases
are stable at room temperature for different Te content, have been
studied, without any intentional manipulation on carrier concentration.
It is found that the three phases show intrinsically different hole
concentrations: ∼1016 cm–3 for
the orthorhombic phase but as high as 1021 cm–3 for the hexagonal and rhombohedral phases. Ge-rich status in the
orthorhombic phase and Ge-poor status in hexagonal and rhombohedral
phases may be responsible for the huge difference in hole concentrations.
The rhombohedral phase shows a much higher Seebeck coefficient than
the hexagonal phase with similar hole concentration, indicating that
the profile of valance band maximum for the rhombohedral structure
is more favorable for high TE performance than the hexagonal phase
in GeSe1–xTex. The highest zT of 0.69 has been obtained
in GeSe0.55Te0.45 at 778 K, at which temperature
the rhombohedral phase has already transformed to a cubic phase; however,
a zT value of 1.74 at 628 K is predicted by the quality
factor analysis for rhombohedral GeSe0.55Te0.45 if optimum hole concentration can be achieved.