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Annealing of Strontium Titanate Based Thermoelectric Materials by Graphite: Mechanistic Analysis by Spectroscopic and Chromatographic Techniques
Author(s) -
Lee Alex Chinghuan,
Qin Mengjie,
Li Haoran,
Shi Zongmo,
Xu Jie,
Gao Feng,
Chen Yongsheng
Publication year - 2020
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.202000113
Subject(s) - graphite , annealing (glass) , strontium titanate , chemistry , ceramic , analytical chemistry (journal) , thermoelectric effect , chemical engineering , combustion , materials science , nanotechnology , chromatography , organic chemistry , thin film , metallurgy , physics , engineering , thermodynamics
Strontium titanate (SrTiO 3 ) 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 N 2 with graphite) and quantify the various gases evolved in the process. It is shown that reducing agents, H 2 and CO (concentrations peaked at ca. 0.4–0.5 %), are generated from graphite in the annealing process. H 2 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 SrTiO 3 ‐based ceramic with graphite, higher levels of H 2 O and CO 2 are detected, which is resulted from the reduction of the ceramic by H 2 and CO, respectively. About 67 % of the oxygen vacancies were created by CO reduction while about 33 % by H 2 reduction. The conclusions are well supported by direct weight loss measurements with a difference of less than 6 %.