  High-performance thermoelectric oxides could offer a great energy solution
for integrated and embedded applications in sensing and electronics industries.
Oxides, however, often suffer from low Seebeck coefficient when compared with
other classes of thermoelectric materials. In search of high-performance
thermoelectric oxides, we present a comprehensive density functional
investigation, based on GGA$+U$ formalism, surveying the 3d and 4d
transition-metal-containing ferrites of the spinel structure. Consequently, we
predict MnFe$_2$O$_4$ and RhFe$_2$O$_4$ have Seebeck coefficients of $\sim \pm
600$ $\mu$V K$^{-1}$ at near room temperature, achieved by light hole and
electron doping. Furthermore, CrFe$_2$O$_4$ and MoFe$_2$O$_4$ have even higher
ambient Seebeck coefficients at $\sim \pm 700$ $\mu$V K$^{-1}$. In the latter
compounds, the Seebeck coefficient is approximately a flat function of
temperature up to $\sim 700$ K, offering a tremendous operational convenience.
Additionally, MoFe$_2$O$_4$ doped with $10^{19}$ holes/cm$^3$ has a calculated
thermoelectric power factor of $689.81$ $\mu$W K$^{-2}$ m$^{-1}$ at $300$ K,
and $455.67$ $\mu$W K$^{-2}$ m$^{-1}$ at $600$ K. The thermoelectric properties
predicted here can bring these thermoelectric oxides to applications at lower
temperatures traditionally fulfilled by more toxic and otherwise burdensome
materials.
