Neutron Scattering Studies of Short-Range Order and Atomic Displacements in a Null-Matrix ⁶¹Ni_0.52 Pt_0.48 Crystal

J. A. Rodriguez, S. C. Moss, J. L Robertson, J. R. D. Copley, D. A. Neumann,

J. Major

The best known exception to the Heine-Samson and Bibier-Gauther arguments for ordering effects of transition metals (similar to the Hume-Rothery rules) is a NiPt alloy, where the phase diagram is similar to the CuAu system. Using the Disk Chopper Spectrometer (DCS) at NIST, we have investigated a Null-Matrix Crystal ⁶¹Ni_0.52 Pt_0.48 has a negative scattering length, nearly equal in magnitude to Pt). The composition has thus been chosen whereby all effects depending on the average lattice scattering vanish. The only remaining contributions to the diffuse scattering are the Short Range Order (SRO) and Size Effect (SE) terms. Such data permit the extraction of the SRO parameters (concentration correlations) as well as the displacement parameters (concentration-displacement correlations). Using the Krivoglaz-Clapp-Moss theory, we obtained the Effective Pair Interactions (EPI). The results can be used to model the alloy in the context of electronic theory of alloy phase stability, including the very important aspect of charge transfer and ionicity.

Author: Dr. Jose Abelardo Rodriguez

Mentor: Dr. Jeffrey Lynn

Division: NIST Center for Neutron Research

Laboratory: Material Science and Engineering

Bldg. 235/ Rm.  A118

Mail Stop: 8562

Telephone: (301) 975 6019

FAX: (301) 921 9847

Email: jose.rodriguez@nist.gov

Sigma Xi member: NO

Category: Materials.