Higher manganese silicides: A Nowotny chimney ladder phase for thermoelectric applications

Nowotny chimney ladder (NCL) phases are intermetallic binary compounds that typically crystallize in a tetragonal crystal structure and constitute of two separate subsystems. The rich solid-state chemistry of NCL phases inherits fascinating lattice dynamics with unique abilities for structural modifications. As an extensively studied energy material for the thermoelectric application, we overview the emerging aspects for structural interpretation in higher manganese silicides (MnSiγ), a prominently explored example of NCL phase. The progress in understanding the incommensurate composite crystals of MnSiγ is discussed to highlight its functional crystallography for proposing the effective strategies to attain favorable modification of transport properties of charge carriers (concentration, mobility, effective mass), and phonons (lattice thermal conductivity). The application potential and prospective strategies for enabling the rational optimization of the dimensionless thermoelectric figure of merit (zT) are examined, and the possibilities of chemical modification in MnSiγ and related NCL phases are presented.