Controlling the Thermoelectric Behavior of La-Doped SrTiO₃ through Processing and Addition of Graphene Oxide

Abstract

The addition of graphene has been reported as a potential route to enhance the thermoelectric performance of SrTiO 3 . However, the interplay between processing parameters and graphene addition complicates understanding this enhancement. Herein, we examine the effects of processing parameters and graphene addition on the thermoelectric performance of La-doped SrTiO 3 (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 strengths (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 than 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 achieving a single-crystal-like temperature dependence of electrical conductivity, implying that 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 2395 S cm −1 and power factor of 2525μW m −1 K −2 at 300 K, with an improved average zT value across the operating temperature range of 300−867 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 modeling using a twophase model implies that the addition of GO can effectively improve carrier mobility in the grain boundary phase. This work provides guidance for the development of high-performance thermoelectric ceramic oxides.

Development and Applications of Thermoelectric Oxide Ceramics and Devices

“…In addition, it has been confirmed that the 2D graphene can be introduced into SrTiO 3based ceramics for grain refinement and promoting more oxygen vacancy formation to enhance carrier mobility [162]. Therefore, SrTiO 3 -based ceramics containing graphite or its derivatives achieve single-crystal-like electron mobility [162][163][164][165] because the delocalization of Anderson localized electrons aided by graphite leads to a manifold improvement in weighted mobility and further the enhanced electron transport properties.…”

Effect of Nanographene Coating on the Seebeck Coefficient of Mesoporous Silicon

“…Recent works have focused on incorporating graphene into matrices such as semiconductor ceramics [ 20 , 21 ]. This incorporation is interesting in combination with porous semiconductors to improve their electronic properties, especially the electrical conductivity, which is initially lowered by nanostructuring [ 22 ] without increasing the thermal conductivity.…”