ABC₆ Type Ordered Structure in Pt-rich Pt-Mn Alloys

抄録

In situ neutron diffraction experiments were performed on single crystals of Pt-12.5 and 14.4 at.% Mn alloys in order to elucidate the ordered structures of Pt-rich Pt-Mn alloys. The observed diffraction patterns at various temperatures up to 1050^ºC have revealed two ordered phases in these alloys. Below the order-disorder transition temperature, a Cu₃Au type ordered structure appears and at low temperature, an ABC₆ type ordered structure with a unit cell 2 × 2 × 2 as large as that of the fundamental fcc cell was found to be stable. A secondary ordering in the alloys is discussed in terms of two order parameters in the ABC₆ type structure utilizing the method of static concentration waves originally proposed by Khachaturyan [Prog. Mater. Sci. 22 (1978) 24]. The ideal alloy composition for the structure is also discussed with the experimentally estimated order parameters.