Characterization of an Atypical Widmanstatten structure in Gd5Si2Ge2 alloys

Bulk microstructures of Gd5Si2Ge2 alloys have been examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microstructure of all samples showed existence of long linear features. The features in general are on the order of one micron or less in width and may be hundreds of microns in length. Oriented single crystals of Gd5Si2Ge2 have been used to study the crystal orientation of the linear features by using a combination of back-reflection Laue X-ray diffraction, SEM and TEM. It has been shown that these linear features grow as thin plates oriented in specific directions. Systematic energy dispersive spectrometry and selected area diffraction studies revealed that these thin plates have an hexagonal crystal structure and a composition consistent with Gd5(SixGe1 - x) 3. These results present the first conclusive identification of this phase and confirm an earlier study that suggested the features might possibly be a Widmanstatten structure that forms during the solidification.