Solid and liquid thermal expansion and structural observations in the quasicrystalline Gd_(84)Yb_(16) compound

摘要

The structure of single-grain Cd_(84)Yb_(16) samples aligned along the twofold and fivefold axes has been followed from 300 to 1050 K using high-energy synchrotron X-rays. The quasicrystal phase is stable up to its melting temperature of 914 K and has a large linear thermal expansion of 37.1 ppm K~(-1) over this temperature range. The samples melt congruently over a temperature range of less than 1 K. The liquid is 7 percent less dense than the solid and. upon cooling from the melt, the quasicrystal phase directly solidifies within a 1 K interval. The amount of undercooling achieved, about 5-25 K, was dependent on the cooling rate. The total scattering function of the liquid is consistent with a dilute liquid Cd structure. These results agree with suggestions that the structure of the liquid must undergo reordering in order to form the solid phases. However, there is no compelling evidence for icosahedral short-range order in the liquid prior to the formation of the quasicrystalline structure.