Extreme Seebeck anisotropy in the quasi-one-dimensional metal, Li$_{0.9}$Mo$_6$O$_{17}$*

We present resistivity and thermopower measurements in the range $300~K\leq T\leq 500$~K on single crystals of the quasi-one-dimensional (q1D) metal, Li$_{0.9}$Mo$_6$O$_{17}$ (LiPB) transverse to the q1D metallic chains. Direct electron transfer between the chains of this material is sufficiently weak that inter-chain transport above 400 K is predominated by thermal activation of valence-band states ($\sim 0.14$~eV below $E_F$), yielding a large, {\emph p}-type inter-chain Seebeck coefficient that coexists with {\emph n}-type metallic behavior confined along the q1D chains. A significant Seebeck anisotropy, $\Delta S\simeq 200\ \mu$V/K, along mutually perpendicular directions gives LiPB potential as a transverse thermoelectric. This anisotropy along with a relatively low inter-chain thermal conductivity $(\kappa\simeq 2$W/mK) results in a substantial transverse Peltier effect.