Crystal growth of manganese silicide, MnSi_∼1.73 and semiconducting properties of Mn₁₅Si₂₆

Abstract

Boules of the most silicon-rich silicide of manganese, MnSi_∼1.73, were grown by the Bridgman method in the composition range from 62.96 to 63.64 at% Si. There are plate-like MnSi precipitates parallel to thec-plane of Mn₁₅Si₂₆ matrix in all boules except at their upper and lower ends. The amount of the MnSi precipitates was about 2 vol%. Measurements of electrical resistivity, Hall coefficient, and thermoelectric power of the boules were made in the temperature range from 77 to 1200 K. Thermoelectronic properties of Mn₁₅Si₂₆ were estimated on the basis of the distribution state of MnSi precipitates in the boule by assuming that metallic MnSi and semiconducting Mn₁₅Si₂₆ alternately crystallized in lamellae. Although the resistivities and thermoelectric powers measured in thec- anda-axis directions of Mn₁₅Si₂₆ showed anisotropy, the former were proportional to exp (4073/T) in the intrinsic region in both directions. The Hall coefficients showed isotropy over the whole temperature range. The degenerate holeconcentration of Mn₁₅Si₂₆ was determined to be 2.1×10²⁷ m⁻³. Hall mobilities of Mn₁₅Si₂₆ in both thec- anda-axis directions obey aT ^−3/2-law above 600K. The Hall coefficient calculated from this relationship was in good agreement with the one found for Mn₁₅Si₂₆ in the intrinsic region. The effective-hole masses of Mn₁₅Si₂₆ along thec- anda-axis were found to be, respectively, 15 and 11 times larger than those of a free electron. Assuming that acoustic lattice scattering is dominant and that carriers obey Fermi-Dirac statistics, the temperature dependence of the calculated thermoelectric power was in reasonable agreement with the one estimated for Mn₁₅Si₂₆ in the temperature range from 400 to 1200K.