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, SrTi_0.85Nb_0.15O₃ 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.