High-temperature thermoelectric transport behavior of the Al/γ-Al2O3 interface: impact of electron and phonon scattering at nanoscale metal-ceramic contacts.

The thermoelectric transport properties of a metal-ceramic interface based on Al and γ-Al2O3 are explored by employing the non-equilibrium Green's function formalism (NEGF) coupled with density functional theory (DFT). However, to acquire the phonon thermal conductance, the parameterized ReaxFF potential is utilized for computing the intrinsic force constants of propagating phonons across the interface. Several interfacial electronic properties such as the charge transfer, the potential barrier, and the atomic orbital overlap are critically analyzed based on the DFT derived results of the electrostatic difference potential, the electron density difference, and the spin-polarized density of states in the fully relaxed structure of the interface. Within the NEGF framework, both the electron and phonon transmission coefficients are estimated for the variations of bias voltage and temperature gradient across the interface. The strong orbital overlap and the scattering of electrons and phonons at the nanometer-size interface suppress the lattice thermal conductivity significantly compared to the electron transport, which in turn enhances the thermoelectric performance of the Al/Al2O3 composite, in contrast to the bulk material of Al. Moreover, a steep rise of power factor induced by the increased transmission of charge carriers with temperature improves the energy conversion efficiency of the material. The present findings could pave the way for developing thermoelectric materials based on metal-ceramic composites.