Largely Enhanced Seebeck Coefficient and Thermoelectric Performance by the Distortion of Electronic Density of States in Ge2Sb2Te5

Ping Hu; Tian-Ran Wei; Pengfei Qiu; Yan Cao; Jiong Yang; Xun Shi; Lidong Chen

doi:10.1021/acsami.9b12854

Largely Enhanced Seebeck Coefficient and Thermoelectric Performance by the Distortion of Electronic Density of States in Ge₂Sb₂Te₅

ACS Appl Mater Interfaces. 2019 Sep 18;11(37):34046-34052. doi: 10.1021/acsami.9b12854. Epub 2019 Sep 5.

Authors

Ping Hu^{1

2}, Tian-Ran Wei³, Pengfei Qiu¹, Yan Cao⁴, Jiong Yang⁴, Xun Shi¹, Lidong Chen¹

Affiliations

¹ State Key Laboratory of High Performance Ceramics and Superfine Microstructure , Shanghai Institute of Ceramics, Chinese Academy of Sciences , Shanghai 200050 , China.
² Center of Materials Science and Optoelectronics Engineering , University of Chinese Academy of Sciences , Beijing 100049 , China.
³ State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering , Shanghai Jiao Tong University , Shanghai 200240 , China.
⁴ Materials Genome Institute , Shanghai University , Shanghai 200444 , China.

PMID: 31454228
DOI: 10.1021/acsami.9b12854

Abstract

As one of the state-of-the-art phase-change materials, the stable Ge₂Sb₂Te₅ hexagonal compound also exhibits decent thermoelectric performance with high electrical conductivity and low thermal conductivity. Nonetheless, the excessively high carrier concentration and low Seebeck coefficient are the bottlenecks to achieve high zT values. In this work, with the intention to optimize the electrical properties, indium was introduced as a potentially donor-like dopant in a series of Ge_2-xIn_xSb₂Te₅ samples. The substitution of indium for germanium lowers the density of hole carriers and enhances the Seebeck coefficient. Noticeably, the room-temperature Seebeck coefficient of the doped samples can be three times as large as that of the pristine one, which obviously departures from the theoretically predicted Pisarenko relation based on the single parabolic band model. By virtue of DFT calculations and modeling, the remarkable enhancement of Seebeck coefficient was attributed to the doping-induced local distortion in the electronic density of states. Further insight reveals that indium doping amplifies the bonding character of Ge-Te adjacent to indium and enhances the atomic interaction along the c-axis. Due to the optimized electrical properties as well as the suppressed thermal conductivity, a maximal zT value of 0.78 was achieved in Ge_1.85In_0.15Sb₂Te₅ at 700 K, which is about 40% higher than that of the pristine sample.

Keywords: GeSbTe; bonding character; electronic density of states; resonant level; thermoelectric.