n-type　Mg-2(Si0.4Sn0.6)Bi-x　(0　＜=　x　＜=　0.04)　solid　solutions　with　minute　amounts　of　Bi　were　prepared　by　induction　melting,　melt　spinning　(MS),　and　spark　plasma　sintering　(SPS)　method,　namely　the　non-equilibrium　technique　MS-SPS,　using　bulks　of　Mg,　Si,　Sn,　Bi　as　raw　materials;　the　phase　components,　microstructures　as　well　as　the　thermoelectric　properties　were　systematically　investigated.　The　multiple　localized　nanostructures　within　the　matrix　containing　nanoscale　precipitates　and　mesoscale　grains　were　formed,　resulting　in　remarkably　decreasing　of　lattice　thermal　conductivities,　particularly　for　samples　with　the　nanoscale　precipitates　having　the　size　of　10-20　nm.　Meanwhile,　the　electrical　resistivity　was　reduced　and　the　Seebeck　coefficient　was　increased　by　Bi-doping,　causing　improved　electrical　performance　for　the　Mg-2(Si0.4Sn0.6)Bi-x　(0　＜=　x　＜=　0.04)　compounds.　The　dimensionless　figure　of　merit　ZT　was　significantly　improved　and　the　maximum　value　reaches　1.20　at　573K　for　the　Mg-2(Si0.4Sn0.6)Bi-0.03　sample,　greatly　higher　than　that　of　the　non-doped　samples.　(C)　2013　AIP　Publishing　LLC.