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research papers
Atomic arrangements of long-period superstructures in Au-24.5at.%Cd alloy with the basic h.c.p. structure have been investigated by high-resolution electron microscopy. The alloy shows one-dimensional or two-dimensional long-period superstructures in the close-packed plane with a 6H stacking sequence, depending on heat treatments. It is shown that the two-dimensional incommensurate superstructure with a period larger than 9a0 is composed of domains of the hexagonal commensurate structure (M = 9) separated by the antiphase-boundary zone in which 33/2a0 × 2a0 × 3c0 orthorhombic structure is formed (a0, c0 being the lattice parameters of the h.c.p. structure). Microstructures of the alloy annealed at 620 K with the one-dimensional long-period superstructure and of the alloy quenched from 770 K showing diffuse scattering have also been investigated by high-resolution electron microscopy.