Lattice anharmonicity in charge compensated higher manganese silicide single crystals

Abstract

Lattice anharmonicity driven by weakening interatomic interactions inherits an intrinsically low lattice thermal conductivity in a crystal. In this work, we demonstrate the efficacy of V (hole-doping) and Fe (electron-doping) co-substitutions on the Mn-sites for realizing charge compensation and lattice anharmonicity in p-type higher manganese silicide (HMS) single crystals melt grown employing the Bridgman method. A higher power factor sustained by optimal valence electron count (VEC) through charge compensation along with a significant reduction in lattice thermal conductivity promoted by local ordering or atomic clustering-induced lattice anharmonicity has enabled the attainment of an unprecedentedly higher thermoelectric figure-of-merit (zT) ∼0.75 (±0.1) at 873 K in partially substituted (Mn_0.94V_0.03Fe_0.03)Si_1.74 single crystals, corresponding to ∼300% enhancement over pristine MnSi_1.74. The inherent structural modulation and incommensurate periodicities were assessed employing the Le Bail analysis within the framework of a (3 + 1)-dimensional superspace approach and interpreted by following the 14-electron rule for Nowotny chimney ladder phases to reveal the structure–property correlations. These findings provide a greater understanding of the interrelations between crystal structure, chemical bonding, and lattice dynamics in HMSs, a prominent example of the Nowotny chimney ladder phase for thermoelectric applications.