LOCAL LATTICE DISTORTION IN ORDERED AND DISORDERED CU3PD ALLOYS

We have combined extended X-ray absorption fine structure (EXAFS) and electron diffraction to study both ordered and disordered Cu3Pd, and h ave established that in the first shell of neighbours the Cu-Pd distan ce is approximately 0.03 angstrom greater than that for Cu-Cu. This re sult lends support to recent theoretical treatments which assume a dis tribution of bondlengths in disordered alloys, and draws attention to the fact that Vegard's law does not require a single, mean bondlength, as assumed in the application of mean-field theories.