Transmission electron microscopy of vanadium-silicon (V 3 Si) at low temperatures

Abstract

It is shown that using a double tilting specimen holder cooled by liquid helium it is now possible to undertake the same kinds of study by transmission electron microscopy at very low temperatures as can be carried out at room temperature. The technique has been applied to a detailed study of the microstructure formed during the martensitic phase transformation in thin foils of the intermetallic compound vanadium-silicon V$_3$Si (superconducting transition temperature 17 $^\circ$K) in the temperature range 11 to 29 $^\circ$K. The material has been found to transform into twin related lamellae, sometimes only 100 $\overset{\circ}{mathrm A}$ thick, the twin planes being {110}. The preferred {110} twin plane varies from region to region in the specimen, and in some areas lamellae parallel to different {110} planes interpenetrate. Cine techniques were used to record the changes in structure taking place during the transformation. The contrast effects observed are interpreted: (i) by application of the theory developed by Gevers, Delavignette, Blank, Van Landuyt & Amelinckx (1964a, b) for single inclined coherent twin boundaries; (ii) by extension of this theory to the case of an overlapping pair of inclined twin boundaries; and (iii) by direct application of the dynamical theory of electron diffraction to twin related regions with twin boundaries nearly parallel to the electron beam.