Enhanced thermoelectric performance of p-type filled skutterudites via the coherency strain fields from spinodal decomposition

Abstract Here we demonstrate that the coherency strain fields arising from spinodal decomposition can improve simultaneously the electronic density of states (DOS) near the Fermi level and the phonon-scattering rate in p-type filled skutterudites. Spinodal decomposition is appeared in the p-type filled skutterudite La_0.8Ti_0.1Ga_0.1Fe₃CoSb₁₂, which is produced by a combination of water-quenching, long-term annealing and hot-pressing approaches. Within each grain of the hot-pressed sample, there are La-poor and La-rich skutterudite phases. The size of each phase is then substantially reduced to about 200 nm by using rapid solidification of melting-spinning followed by hot-pressing method. Therefore, the coherency strain fields resulted from spinodal decomposition is significantly increased. High resolution transmission electron microscopy (HRTEM) reveals that most of these domains are in the state of tensile. Compared to the quenched sample, the Seebeck coefficient increases about 10% and the lattice thermal conductivity of the optimization sample is reduced about 30% at 700 K. Our theoretical analysis shows that grain boundary scattering has limited contribution to the reduction of lattice thermal conductivity in p-type filled skutterudites. The drastic reduction in the lattice thermal conductivity is mainly caused by phonon scattering through the coherency strain fields. As a result, a peak ZT of about 1.2 at 700 K is obtained in the spun sample. In addition, the spun sample displays good repeatable and stable characteristics.