{112} 〈111〉 twins in tetragonal MoSi2

Abstract

Plasma-sprayed tetragonal MoSi₂ has been examined by transmission electron microscopy. Growth twins are commonly observed in the microstructure. Analysis of diffraction patterns using a stereographic projection indicates that the twinning plane is {112} and the twinning direction is 〈111〉. Atomic modelling of the twin interface shows that a key element is the pseudo-hexagonal nature of the MoSi₂{110} planes which allows a ∑2 coincidence site relationship between matrix and twin. The habit plane for the twins is commonly observed to be {110}, implying that the plane corresponds to a twist boundary. The rotation angle is almost exactly 60°. It is likely that the twins result from the hexagonal-to-tetragonal transformation of MoSi₂ at high temperatures.