Structure of long period superstructure in Cu-rich γ-brass investigated by electron diffraction

Striped type of long period superstructure (LPS) in Cu-rich γ-brass is investigated by the analysis of electron diffraction patterns taken from various beam directions. In spite of one-dimensional LPS, two modulation waves which slightly deviate from the [101] and [011] directions play an important role in formation of the LPS. The structure is characterized by alternately periodic arrays of inversion antiphase boundaries with two displacement vectors of 1/6 [111] and 1/6 [111]. The displacement vectors are apparently different from each other but are crystallographically equivalent, resulting in that the LPS has a centrosymmetry as a whole. The two modulation waves are associated with the arrangement of average vacancy planes. Through such a rearrangement of structural vacancies, the deficiency of electron concentration in the Cu-rich γ-brass is considered to be compensated.