Annealing of Strontium Titanate Based Thermoelectric Materials by Graphite: Mechanistic Analysis by Spectroscopic and Chromatographic Techniques

Alex Chinghuan Lee; Mengjie Qin; Haoran Li; Zongmo Shi; Jie Xu; Feng Gao; Yongsheng Chen

doi:10.1002/cplu.202000113

Annealing of Strontium Titanate Based Thermoelectric Materials by Graphite: Mechanistic Analysis by Spectroscopic and Chromatographic Techniques

Chempluschem. 2020 Apr;85(4):734-741. doi: 10.1002/cplu.202000113.

Authors

Alex Chinghuan Lee^{1

2}, Mengjie Qin³, Haoran Li¹, Zongmo Shi³, Jie Xu³, Feng Gao³, Yongsheng Chen¹

Affiliations

¹ Energy and Catalysis Laboratory, Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, P. R. China.
² Hierarchical Green-Energy Materials (Hi-GEM) Research Center, National Cheng Kung University, Tainan, 70101, Taiwan, P. R. China.
³ State Key Laboratory of Solidification Processing, MIIT Key Laboratory of Radiation Detection Materials and Devices, USI Institute of Intelligence Materials and Structure, NPU-QMUL Joint Research Institute of Advanced Materials and Structure, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, 710072, P. R. China.

PMID: 32286741
DOI: 10.1002/cplu.202000113

Abstract

Strontium titanate (SrTiO₃ ) based materials are promising for high-temperature thermoelectric applications. In order to enhance their performance, annealing is usually required and carried out under various atmospheres. Annealing with graphite is quite effective, but the mechanism is not yet clear. In this work, we use IR spectroscopy and gas chromatography (GC) to monitor the chemical environment under the annealing conditions (1350 °C for 8 h under 16.9 mL/min N₂ with graphite) and quantify the various gases evolved in the process. It is shown that reducing agents, H₂ and CO (concentrations peaked at ca. 0.4-0.5 %), are generated from graphite in the annealing process. H₂ is produced in carbon gasification reaction, which also generates CO. Additional CO is produced from incomplete combustion of carbon. In the annealing of a La-doped SrTiO₃ -based ceramic with graphite, higher levels of H₂ O and CO₂ are detected, which is resulted from the reduction of the ceramic by H₂ and CO, respectively. About 67 % of the oxygen vacancies were created by CO reduction while about 33 % by H₂ reduction. The conclusions are well supported by direct weight loss measurements with a difference of less than 6 %.

Keywords: Annealing; IR spectroscopy; carbon gasification; strontium titanate; thermoelectric materials.

Abstract

Grants and funding