Effect of graphene oxide and carbon black on the thermoelectric performance of niobium doped strontium titanate

Strontium titanate-based ceramics are promising n-type thermoelectrics due to their low cost and high thermal and chemical stability. Here, SrTi0.85Nb0.15O3 was prepared with carbon additions of electrochemically produced graphene oxide (eGO) and commercially available carbon black (CB). Ceramic samples were sintered at 1700 K under a reducing atmosphere. XRD, HR-TEM and Raman spectra confirmed the matrix phase was cubic perovskite; there were no carbon residues. By incorporating graphene oxide, the electrical conductivity increased nine-fold to 2818 S cm−1 at 300 K as a result of enhanced carrier mobility. In contrast, the carbon black samples exhibited low density and a small average grain size of ∼1 μm. High-resolution X-ray photoelectron spectroscopy revealed the presence of a large number of ionised impurities in the carbon black samples, which significantly enhanced scattering effects; low thermal conductivities of 1.7 W m−1 K−1 were achieved at 873 K. The work reveals that eGO promotes charge transport in SrTiO3, while CB significantly suppresses phonon transport. Both effects are relevant to the development of other thermoelectrics.