Interpretation of thermoelectric power behaviour of Zinc nanowire composites: Phonon-scattering mechanism

We develop a theoretical model for quantitative analysis of temperature-dependent thermoelectric power (S) of Zn nanowires. In doing so, we first use the Mott expression to compute the electron diffusive thermoelectric power (S_c^diff.) using Fermi energy as electron-free parameter, S_c^diff. shows linear temperature dependence. Further, the S_c^diff. contribution is subtracted from the experimental data and the difference (S_experimental-S_c^dif) is characterized as phonon drag thermoelectric power (S_ph^drag) which is obtained within the relaxation time approximation where the thermoelectric power is limited by the scattering of phonons with impurities, grain boundaries, charge careers and phonons in the nanowires. The S_ph^drag shows anomalous temperature-dependent behaviour, which is an artifact of various operating scattering mechanisms. The observed anomalies are well accounted in terms of interaction among the phonons-impurity, phonon-grain boundaries, phonon-electron and the umklapp scattering. It is also shown that for phonons the scattering and transport cross-sections are proportional to ω⁴ in the Rayleigh regime where ω is the frequency of the phonons. Numerical analysis of thermoelectric power from the present model shows similar results as those revealed from experiments.