X-ray intensity fluctuation spectroscopy (XIFS) has been used to study the ordering kinetics in single-crystal bulk Cu₃Au. The order-disorder phase transition in Cu₃Au is a classic case study for a discontinuous phase transition with non-conserved order-parameter. At high temperatures the alloy has a fcc lattice with each site randomly occupied by either a Cu or an Au atom. Below a critical ordering temperature, the system develops long-range order. The Au atoms tend to occupy the corners of the fcc lattice while the Cu atoms will locate themselves at the face sites.

On average, the development of order in such a system follows a universal behavior which can be measured by standard (incoherent) X-ray diffraction. By using coherent scattering, we were able to measure fluctuations around the average behavior of the ordering kinetics. Two-time correlation functions of the speckle intensities were measured from the scattering data and were found to agree well with a theoretical scaling function previously predicted by a research group led by our noteworthy chair ;-)

More details and many colorful pictures after pizza on Monday! :-)

Monday, November 11th 2002, 12:30
Ernest Rutherford Physics Building, Boardroom (room 104)