Neutron Diffraction Study of Short-Range Order inβ-CuZn

Abstract

Neutron diffuse scattering measurements have been made on an isotopically enriched single crystal of $\beta$ CuZn at a series of temperatures above $T_c$. The observed short-range order scattering exhibited the general characteristics of critical scattering, quite unlike the diffuse scattering reported for any other ordering alloy, and confirmed that the order-disorder transformation in this alloy is a phase transformation of second (or higher) order. No quantitative evaluation of the short-range order parameters from the measured scattering was possible. A comparison of the measured scattering with calculations based on the theories of Zernike, Cowley, and Elliott and Marshall showed rather good agreement, suggesting that these simple theories give a reasonable approximation to the actual short-range order correlations above $T_c$. From a consideration of the discrepancies between these theories and the experimental data, it appears that at temperatures above $T_c$ the Ising model forms a surprisingly good model for this alloy.