Multi-strategy cooperative optimization of thermoelectric performance in higher manganese silicide-based materials

Abstract

Higher manganese silicide (HMS), a naturally abundant p-type thermoelectric (TE) material, exhibits an eco-friendly profile, low production cost, superior mechanical strength, and high thermal stability. Current strategies for enhancing the TE performance of HMSs focus on optimizing dopants for anionic/cationic substitution and nanocomposite engineering. Nevertheless, the cost-prohibitive nature of requisite dopants and nanocomponents, coupled with intricate synthesis routes, impedes their practical deployment. In this study, V-Al-co-doped HMS bulk specimens incorporated with CrSi2 are consolidated by spark plasma sintering following wet ball milling. This strategy employs dual-site doping, with V substituting at cationic Mn sites and Al at anionic Si sites to achieve acceptor doping, thereby increasing the hole concentration. Concurrently, CrSi2 nanoparticle incorporation enhances phonon scattering at grain boundaries, significantly suppressing lattice thermal conductivity (κl). Furthermore, both V and Cr interact with Mn, respectively, forming resonant states near the Fermi level and ultimately resulting in overlapping of the energy levels. At 823 K, the (Mn0.985V0.015) (Si0.99Al0.01)1.79 + 20% CrSi2 composite achieved a peak zT value of 0.72, a 71.4% enhancement over the pristine MnSi1.79 matrix. Consequently, synergistic cation–anion site engineering coupled with nanostructured composite design provides an effective strategy for enhancing the TE performance of HMSs, leveraging defect-mediated carrier optimization and phonon scattering intensification.