Insititude of Materials Science, University of Tsukuba^* Center of General Education and Humanities, Tokyo University of Science, Japan^** Institute for Materials Research, Tohoku University, Japan^***
○Yin Suo^* Rokuro Miida^** Toetsu Shishido^*** Ken-ichi Ohshima^*

Pd-Mn alloy system has complicated phases and structures. It presents α₁, β₁, β₂, and β₃ phases among 20-60 at. % Mn [1]. There are few reports on β₂ phase (Pd₂Mn) [2], so that more detailed X-ray diffraction experiments should be performed for understanding of the structural characteristics. We have, therefore, measured the X-ray diffuse scattering intensity distributions from a single crystal of disordered Pd₂Mn alloy, whose specimen was quenched into iced water from 1000^oC. Cigar-like intensity distributions along the [010] direction at (100) and other equivalent positions were observed, which are due to an atomic short-range order (ASRO). With using Borie-Sparks' method, the ASRO intensity was separated from the total diffuse scattering intensities. Warren-Cowley ASRO parameters were determined up to the 50th neighbor. It is of characteristic that the values of α(l00) parameters (l = even number) are lager than those of the others. The X-ray diffraction intensity data for a specimen, annealed at 600^oC, were also collected to determine the average structure of β₂ phase.
[1] R. Miida, T. Tajima, D. K. Saha, M. Y. Wey, D. Watanabe and K. Ohshima: Materials Transactions, 45, 9 (2004) 2822.
[2] G. Kadar, E. Kren and M. Marton: J. Phys. Chem. Solids, 33 (1972) 212.