On the System Silicon–Ytterbium: Constitution, Crystal Chemistry, and Physical Properties

Abstract

Phase equilibria in the silicon-rich part of the system Si–Yb (>60 at.% Si) have been established from DTA, LOM, EMPA, and X-ray diffraction experiments on arc-melted and annealed bulk alloys as well as on single crystals grown from pure gallium or indium metal used as a flux solvent. Phase relations are characterized by the existence of a defect disilicide showing polymorphism. Yb3Si5, the low-temperature modification with Th3Pd5 type, is a line compound at 62.5 at.% Si, stable below 947±7°C. Above this temperature Yb3Si5 transforms into the YbSi2−x (defect AlB2-derivative type) corresponding to a peritectoid equilibrium at 947±7°C: YbSi2−x+YbSi⇔Yb3Si5. YbSi2−x exhibits a small homogeneity region from ∼62.5 at.% to ∼63.5 at.% Si and melts incongruently at 1408±9°C at ∼63 at.% Si. On cooling it decomposes according to a eutectoid reaction at 763±7°C: YbSi2−x⇔Yb3Si5+(Si). The silicon-rich part of the diagram is characterized by a eutectic equilibrium at 1135+7°C and ∼81 at.% Si: L⇔YbSi2−x+(Si). From magnetic susceptibility and electrical resistivity measurements, performed on single-crystalline specimens, Yb3Si5 was found to be an intermediate valent system.