Structures at Glassy, Supercooled Liquid, and Liquid States in La-Based Bulk Metallic Glasses

Local atomic structures at glassy, supercooled liquid, and liquid states for La-based bulk metallic glasses (BMGs) have been investigated by in-situ high-temperature X-ray diffraction. It is found that the coordination number of about 15.1 +/- A 0.1 for the La62Al14Cu11.7Ag2.3Ni5Co5 alloy does not depend on temperature up to liquid temperature, while it decreases slightly with temperature for the La62Al14Cu24 and La62Al14Cu20Ag4 alloys. The S(q) data recorded at the supercooled liquid region can be well described by the Debye theory. For the three alloys, the volume expansion coefficient and the slopes of radii variation for the first to third nearest neighboring coordination shells show differences at glassy-to-supercooled liquid transition, while no obvious changes were detected at supercooled liquid-to-liquid transition for them. The linear expansion coefficient value (beta = 1.6 +/- A 0.1 x 10(-5) K-1) below the glass transition temperature deduced from S(q) data is consistent with that detected by the dilatometer (beta = 1.25 x 10(-5) K-1) for the La62Al14Cu11.7Ag2.3Ni5Co5 BMG.