Abstract
Higher Manganese Silicides (HMS) have been revealed as composite crystals consisting of two tetragonal subsystems of [Mn] and [Si] with an irrational c-axis ratio γ = c_<Mn>/c_<Si> 〜 1.73. The structure formula is thus expressed as MnSi_γ. Due to a significant positional modulation of Si atoms while maintaining the carrier conduction paths of Mn atoms, the concept of phonon glass and electron crystal (PGEC) is actually realized in the present unique crystal structure. Atomic-, unit cell- and micron-scale modulation can be applied to the HMS-based thermoelectric materials to minimize the lattice thermal conductivity together with to optimize the electronic structure, and hence maximize the dimensionless figure-of-merit.
