Niobium(V) oxide with added silver as a thermoelectric material prepared by spark plasma sintering

• Nb2O5/Ag composites were synthesized by spark plasma sintering.
• Increases in both σ and S were realized, provided the Ag particles did not form current bypasses.
• The increase in κ was suppressed by controlling the dispersion of Ag particles.
• The introduction of a metal into an insulator by SPS causes it to become a thermoelectric material.

Niobium oxide (Nb2O5) and silver (Ag) composites with different amounts of incorporated Ag (up to 19.2 wt%) were synthesized by spark plasma sintering (SPS) with the aim of realizing a thermoelectric material. The electrical conductivity (σ) increased with increasing Ag content, whereas the Seebeck coefficient (S) increased then decreased. It is plausible that the highly conductive Ag particles, introduced between the Nb2O5 grains through mechanical milling of the Nb2O5 and Ag2O raw materials, contributed the increases in both σ and S. However, upon further increasing the amount of Ag, the Ag particles became connected with each other and acted as bypasses for carrier transport, thus increasing σ and decreasing S. The thermal conductivity (κ) increased with the Ag content; however, the rate of increase was small when the Ag particles were not connected with each other. Our findings demonstrate that the introduction of a metal into an insulator by SPS causes it to become a thermoelectric material.