Metastable phases in the crystallization of amorphous Pd80Si20 alloy

Two metastable phases have been determined during the crystallization of amorphous Pd80Si20 alloy using transmission electron microscopy. The primitive orthorhombic (PO) metastable phase forms when annealing the sample at 340 degrees C. Its unit-cell parameters are a = 0.47 nm, b = 1.35 nm and c = 1.67 nm with a space group of either Pnmm or Pn2(1)m. The primitive monoclinic metastable phase forms at an annealing temperature of 480 degrees C. The parameters for the PM phase unit cell are: a = 0.47 nm, b = 0.92 nm, c = 1.67 nm, alpha = beta = 90 degrees and gamma = 101.6 degrees with a space group P2(1) or P2(1)/m. During the crystallization process, a transition state (TS) has been found, which is a mixture of PO and PM phases. In the TS, the unit cells of the PO and PM phases are interlaced irregularly with the common a-c plane. This TS explains the MS-II and Pd9Si2 phases reported by Masumoto and Maddin in 1971 and Duhaj, Barancok and Ondrejka amorphous --> PO --> PO + Pd3Si --> TS + Pd3Si --> PM + Pd3Si --> Pd9Si2 + Pd3Si.