RECOVERY OF STATIC ATOMIC DISPLACEMENTS IN Fe-Ni SOLID SOLUTIONS WITH THE 3[[lambda]] TECHNIQUE. G. E. Ice, X. Jiang, L. Robertson, C. J. Sparks, P. Zschack, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6118, USA

The use of resonant-scattering techniques to recover local pair displacements and local chemical order has brought new and useful information to our understanding of crystalline solid solutions. It has been long recognized that "atom size differences" move the atoms off the sites of the average lattice and play an important role in alloy properties and in phase stability. Most of the information about atomic size differences comes from the change in lattice parameter with elemental concentration. The success of Vegard's law in fitting this mostly straight line relationship of lattice parameter versus concentration is found to be fortuitous in the Fe-Ni system. Neither the like pair distance (AA and BB pairs) is independent of concentration nor is the AB pair separation the mean between the pure elements as predicted by Vegard's law. Mathematical treatment of the data is discussed and both the systematic and statistical errors are assessed. Concern with the inelastic processes such as resonant Raman, Compton and plasmon scattering contributions to the diffuse scatter is important to the recovery of the weak elastic scattering. Resonant (anomalous) x-ray scattering near absorption edges is used to effect contrast changes in the Laue scattering needed to unravel the individual pair displacements.

Research sponsored by the Division of Materials Sciences, U.S. Department of Energy under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corporation.