Large Thermoelectric Figure of Merit in Thin Ablated Skutterudite Films

Thin 40{\%} lanthanum-filled skutterudite films were prepared by pulsed laser ablation on glass substrates. In general, laser ablated film characteristics exhibit up to 70{\%} amorphous structure and vary in thickness by about 20{\%} from center to edge. The thermoelectric figure of merit was determined using Harman's$^{1}$ method at room temperature, which involves voltage measurement under isothermal and adiabatic conditions. A total of 16 samples prepared in three ablation runs were measured as a function of substrate thickness in order to determine the limiting figure of merit (\textit{ZT = S}$^{2}$\textit{T/$\rho \kappa $}${\rm p}{\rm g}$n the thin film geometry. The average film thickness was determined to be 95 \textit{nm}. The extrapolated behavior predicts a very large value of the thermoelectric figure of merit for this material, approaching 15, far exceeding values obtained with bulk samples. We attribute the high value to several possible factors: enhanced Seebeck coefficient and size limited thermal conductivity in both electronic and lattice components. Possible applications are discussed. 1. T. C. Harman, S. E. Miller, H. L. Goering, \textit{J. Phys. Chem. Solids},\textbf{ 2}, 181 (1957).