Study of doped higher manganese silicides crystals by transmission electron diffraction and electron backscatter diffraction

Abstract

The microstructure of Al-, Ge-, and Mo-doped higher manganese silicide crystals (HMS), grown by the Bridgman method have been investigated by transmission electron diffraction, electron backscatter diffraction, scanning electron microscopy, and X-ray energy-dispersive spectrometry. It is shown that the matrix crystal has the Mn₄Si₇ structure. The introduction of Ge and Mo impurities into an HMS crystal results in the precipitation of Si-Ge solid solution and molybdenum disilicide. The size of precipitates varies in a wide range: from several nanometers to several hundreds of micrometers. The following orientation relationships between Ge-Si precipitates and the Mn₄Si₇ crystal were determined: (112)$[\bar 110]$ Ge-Si ‖ (010)[100] Mn₄Si₇. Polycrystalline MoSi₂ precipitates form a multicomponent texture along the [001] Mn₄Si₇ direction. Small amounts of cubic MnSi and Al-Mn-Si alloy precipitates were revealed. In addition, Al oxide was observed mainly in crystal pores. It is shown that 0.5–0.8 at % Al, 0.4–0.6 at % Mo, and 1.5–2.0 at % Ge impurities are incorporated into the Mn₄Si₇ lattice.