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DY: Dynamik und Statistische Physik

DY 15: Kritische Ph
änomene und Phasenumwandlungen I

DY 15.4: Vortrag

Montag, 11. März 2002, 15:15–15:30, H3

Dynamics of Critical Fluctuations Observed by X-ray Microdiffraction — •C. Mocuta¹, H. Reichert¹, M. Drakopoulos², M. Denk¹, and H. Dosch¹ — ¹MPI für Metallforschung, D-70569 Stuttgart, Germany — ²ESRF, F-38043 Grenoble, France

Using a new experimental technique we have studied the intensity fluctuations originating from critical fluctuations in Fe₃Al, which exhibits an order-disorder phase transition (DO₃-B2, T_C = 780 K). The central idea of the technique is to probe a region small enough that the relative number of fluctuating domains (δN/<N>) of a certain size is large. This is achieved by increasing the maximum length scale of the fluctuations (by approaching T_C) and reducing the probed sample volume (thus <N>). In the experiments we used a well focused beam (micron size) to probe a very thin (sub-micron) single crystalline sample. Upon approaching T_C the number of ordering fluctuations (on the length scale of the correlation length ξ) is small in this volume. Pronounced effects on the intensity of a superstructure peak (characteristic for the chemical order) were measured. The data sets allow the determination of time correlation functions which are attributed in a direct way to the dynamical behavior of the fluctuations on a given length scale. The experiments demonstrate the potential of partially coherent x-ray microbeams for the direct observation of critical phase transition / fluctuation phenomena.