Structure and phase transformation of melt-spun Gd5Si2Ge2

Gd5Si2Ge2 materials were prepared by rapid solidification at different wheel speeds. The crystal phase and phase transformation of the rapidly solidified materials have been investigated by powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The materials contained mainly a Gd5Si2Ge2-type single phase at a wheel speed of 20 m/s; a Gd5Si4-type major phase and a Gd5Si2Ge2-type minor phase at 30 m/s; a Gd5Si4-type single phase at 40 m/s; and Gd5Si4-type and Gd5Si2Ge2-type double phase at 50 m/s. A first-order phase transformation occurred at approximately 273 K in the materials prepared at a wheel speed of 20 m/s whereas a second-order phase transformation appeared at approximately 290 K in the materials prepared at other wheel speeds. Furthermore, we observed some exothermic peaks located at similar to 250-300 degrees C in the DSC curves for all the melt-spun samples. These exothermic reactions can be attributed to the crystallization of a small amount of glassy phase. The presence of glassy phase has been confirmed by both the electron diffraction pattern observed in the TEM observation and the glass transition found in the DSC scan. (c) 2006 Published by Elsevier B.V.