The addition of graphene has been reported as a potential route for enhancing the thermoelectric performance of SrTiO3. However, the interplay of processing parameters and graphene addition complicates the understanding of this enhancement. Herein, we examine the effects of processing parameters and graphene addition on the thermoelectric performance of La-doped SrTiO3 (LSTO). Briefly, two types of graphene oxide (GO) at different oxidation degrees were used while the LSTO pellets were densified under two conditions with different reducing strength (with/without using oxygen scavenging carbon powder bed muffling). Raman imaging of the LSTO green body and sintered pellets suggests that the added GO sacrificially reacts with the lattice oxygen, which creates more oxygen vacancies and improves electrical conductivity regardless of the processing conditions. The addition of mildly oxidized electrochemical GO (EGO) yields better performance compared with the conventional heavily oxidized chemical GO (CGO). Moreover, we found that muffling the green body with an oxygen scavenging carbon powder bed during sintering is vital to achieve a single-crystal-like temperature dependency of electrical conductivity, implying a highly reducing environment is critical for eliminating the grain boundary barriers. Combining 1.0 wt% EGO addition with a highly reducing environment leads to the highest electrical conductivity of 2102 S cm−1 and power factor of 2452 µW m−1 K−2 at 300 K, with improved average zT value across the operating temperature range of 300 to 867 K. STEM-EELS maps of the optimized sample show a pronounced depletion of Sr and evident deficiency of O and La at the grain boundary region. Theoretical modelling using a two-phase model implies the addition of GO can effectively improve the carrier mobility in grain boundary phase. This work provides guidance for the development of high-performance thermoelectric ceramic oxides.
|Journal||ACS Applied Materials and Interfaces|
|Early online date||22 Nov 2022|
|Publication status||Published - 7 Dec 2022|
- grain boundary
- graphene oxide