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MM: Fachverband Metall- und Materialphysik

MM 35: Poster Session II

MM 35.41: Poster

Mittwoch, 25. März 2009, 16:30–18:30, P4

Aging dynamics at the martensitic phase transition of Au-Cd quantified by XPCS — •L. Müller¹, M. Waldorf¹, C. Gutt², A. Madsen³, G. Grübel², T.R. Finlayson⁴, and U. Klemradt¹ — ¹II. Physik. Inst., RWTH Aachen Univ. — ²HASYLAB at DESY, Hamburg — ³ESRF, Grenoble — ⁴School of Physics, Univ. of Melbourne

Aging phenomena of martensites have been discussed controversially for decades. Although they were successfully associated with defect-related diffusion processes in the low temperature phase (Ren and Otsuka, Nature 389, 579 (1997)), so far no experiments have directly addressed the characteristic time scales associated with nanoscopic structural changes. Using a Au_50.5Cd_49.5 single crystal X-ray photon correlation spectroscopy (XPCS) measurements in diffraction geometry were carried out at ESRF beamline ID10A. High temperature resolution (0.1 K) and stability (±4 mK) were employed to resolve potential slow dynamics in the vicinity of the phase transition, 2D scattering data close to the (001) Bragg reflection were recorded with a sampling time into the detector of 0.2 s at 1.4 s intervals.

For each temperature one-time correlation functions show significant dynamics only near T_c, being fastest at the transition in disagreement with any critical slowing down scenario. Two-time correlation functions reveal a generally non-stationary behavior and also avalanches in the sample. Characteristic timescales were determined as a function of the aging-time by calculating one-time-correlation functions at a specific age. Fits of Kohlrausch-Williams-Watts functions reveal time constants ranging from ≈400 s to over 6000 s at largest aging-times.