Charge Balanced Vacancy Engineering to Enhance the Thermoelectric Properties of GeMnTe₂

Abstract

As a derivative of GeTe and MnTe, GeMnTe2 exhibits a cubic structure with no phase transition. Compared to GeTe, it is considerably cheaper and has a significantly high carrier concentration compared to MnTe, making it an excellent thermoelectric (TE) material with promising applications. Herein, a charge‐balanced vacancy engineering strategy is employed, resulting in a significant improvement in the power factor of GeMnTe2. Furthermore, the density functional theory calculation shows that the doping of Bi and the absence of Ge synergically increase the density of states near the Fermi level. Power factors of ≈13.7 μW cm−1 K−2 are achieved at 8% Bi content, a 22% improvement compared to the undoped system, while a final maximum ZT value of about 1.12 and an average ZT value of 0.72 are achieved. This indicates that charge‐balance vacancy engineering is an effective optimization method for the GeMnTe2 system, which can effectively improve the TE performance.

Bipolar-like Effect and its Suppression in Magnetic Thermoelectrics GeMnTe2

“…Na x CoO 2 is one of the exceptions to Mott’s theory. The thermoelectric performance of Na x CoO 2 was found to be driven by spin entropy. ,,, Although Na x CoO 2 is a narrow band gap compound, its thermoelectric performance is hardly influenced by the bipolar effect, and its working temperature extends to 1000 K. Another exception is the recently reported GeMnTe 2 . , GeMnTe 2 also has a narrow band gap less than 0.05 eV, while its maximum zT appears above 800 K. GeMnTe 2 has been indicated to be an anomalous thermoelectric material driven by the spin’s thermodynamic entropy …”

“…10,11,35,36 narrow band gap compound, its thermoelectric performance is hardly influenced by the bipolar effect, and its working temperature extends to 1000 K. Another exception is the recently reported GeMnTe 2 . 37,38 GeMnTe 2 also has a narrow band gap less than 0.05 eV, 39 while its maximum zT appears above 800 K. GeMnTe 2 has been indicated to be an anomalous thermoelectric material driven by the spin's thermodynamic entropy. 40 In spite of the high carrier concentration, some studies observed the strong bipolar-like effect in GeMnTe 2 .…”