Thermoelectric Properties of Magnesium Silicide–Based Solid Solutions and Higher Manganese Silicides

CONTENTS 5.1 Mg2Si and its Solid Solutions ........................................................................................... 160 5.1.1 Introduction ............................................................................................................ 160 5.1.2 Fabrication Routes .................................................................................................. 161 5.1.3 Defect Chemistry and Off-Stoichiometry .......................................................... 166 5.1.3.1 Defects in Intrinsic Mg2Si ...................................................................... 166 5.1.3.2 Effect of Doping on Defects ................................................................... 167 5.1.3.3 Effect of Defects on Conduction Type .................................................. 167 5.1.3.4 Effect on Thermoelectric Transport ..................................................... 168 5.1.4 Thermoelectric Transport ..................................................................................... 169 5.1.4.1 Mg2Si ......................................................................................................... 169 5.1.4.2 Solid Solutions of Mg2Si and Mg2Sn ..................................................... 180 5.2 HMS ..................................................................................................................................... 186 5.2.1 Crystal Structure .................................................................................................... 187 5.2.1.1 HMS Nowotny Chimney-Ladder Phases ........................................... 187 5.2.1.2 Incommensurate Phases ........................................................................ 189 5.2.1.3 Modulated Lattice Structure ................................................................. 190 5.2.1.4 Disordered Lattice Structure of HMS .................................................. 191 5.2.1.5 Role of the Atomic Packing Ratio ......................................................... 192 5.2.2 Electronic Structure ............................................................................................... 193 5.2.2.1 Valence Electron Count Concept .......................................................... 193 5.2.2.2 Band Structure ......................................................................................... 194 5.2.2.3 Energy Gap and Carrier Effective Mass .............................................. 194 5.2.3 Phases and Layered Microstructure ................................................................... 195 5.2.3.1 Layered Microstructure of Manganese Monosilicide........................ 195 5.2.3.2 Phase Diagram ........................................................................................ 196 5.2.3.3 Phase Transformations at High Temperature ..................................... 198 5.2.3.4 Phase Stability .........................................................................................200