Long-Period Ordered Structures of the Au-Rich Au-Mn Alloys

Abstract

ABSTRACTChanges in the ordered structures of the Au-Mn system, existing at temperatures below 400°C, with composition have been studied in the range of 20–28 at.% Mn by high-resolution electron microscopy. The superstructures, Au4Mn, Au22Mn6, Au31Mn9 and 2d-APS(I), exist in the range of 20–23 at.% Mn. The Au22Mn6 and Au31Mn9 are the one-dimensional (ld) and two-dimensional (2d) antiphase structure (APS), respectively, based on the Au4Mn, and the 2d-APS(I) is based on the DO22 structure and consists of parallelogram and lozenge shaped domains. When Mn content increases, the Mn-Mn nearest-neighbour pairs are formed across the antiphase boundaries of the 2d-APS(I), and the structure changes to orthorhombic 2d-Au3Mn at about 24 at.% Mn. When Mn content increases further, the Mn-Mn pairs align in the <120> direction and the structure transforms continuously to the monoclinic Au5Mn2.