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M: Metallphysik

M 13: Wasserstoff in Metallen

M 13.5: Vortrag

Montag, 24. März 2003, 15:45–16:00, IFW D

Raman spectroscopy on Mg₂NiH_x switchable mirrors — •A.-M. Carsteanu¹, J. Schoenes¹, S. Enache², and R. Griessen² — ¹Institut für Halbleiterphysik und Optik, TU Braunschweig, Mendelssohnstrasse 3, 38106 Braunschweig, Germany — ²Faculty of Sciences, Division of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands

We have studied the Raman response of the Mg₂NiH_x switchable mirrors as a function of the hydrogen concentration x. This material is known to have a metal-to-insulator phase transition for x>0.3, with an intermediate phase designated as black absorber. The factor group analysis predicts for the hexagonal metallic Mg₂Ni phase, 19 Raman active modes with different symmetries. The same calculations show that the monoclinic insulating phase has 84 Raman active phonons. For the experiments, a micro-Raman spectrometer (Jobin Yvon LabRam HR) has been used. The set-up allows measurements at the laser wavelengths 633, 532 and 325nm. Low temperature spectra display features which are attributed to luminescence, due to their laser wavelength dependence. In the insulating phase, the hydrogen vibrations are identified by the substitution with deuterium. The corresponding Raman lines shift to lower frequency by a factor close to √2. Our results clearly show that Raman spectroscopy is a useful tool in studying this material system also in the black absorber state which is not well known and understood. We acknowledge support by TMR Research Network Metal hydride films with switchable physical properties.