Atomic Short-Range Order in Disordered Pd2Mn Alloy

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 1000oC. 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 600oC, 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.