Structure and phase transformation of melt-spun Gd 5Si 2Ge 2

Abstract

Gd 5Si 2Ge 2 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 Gd 5Si 2Ge 2-type single phase at a wheel speed of 20 m/s; a Gd 5Si 4-type major phase and a Gd 5Si 2Ge 2-type minor phase at 30 m/s; a Gd 5Si 4-type single phase at 40 m/s; and Gd 5Si 4-type and Gd 5Si 2Ge 2-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 ∼250–300 °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.