Regensburg 2010 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 8: Intermetallic Phases II

MM 8.1: Talk

Monday, March 22, 2010, 11:30–11:45, H5

Perturbed γ-γ angular correlation studies of selected 211-MAX phases using ¹¹¹In probes — •Daniel Jürgens¹, Michael Uhrmacher¹, Hans Hofsäss¹, and Jose Mestnik-Filho² — ¹Georg-August-Universität Göttingen, II. Physikalisches Institut, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany — ²Instituto de Pesquisas Energeticas e Nucleares, 05422-970 São Paulo, Brazil

MAX phases are nanolaminated layered carbides and nitrides, which feature an unusual set of the best attributes of both metals and high-performance ceramics. These compounds can be good electrical and thermal conductors, behave elastically stiff as well as high thermal shock resistant. To investigate the local structure of these phases, the technique of perturbed angular correlation (PAC) was used for material characterization beside x-ray diffraction and electron microscopy. Radioactive ¹¹¹In ions, decaying by a γ-γ cascade were implanted into the samples, sensing as spies their local environment via hyperfine interactions. The PAC method was applied to Nb₂InC, Ti₂AlN, Cr₂GeC and Nb₂AsC. Spectra were taken after different annealing steps to determine strength and symmetry of the electric field gradients (EFG) as a fingerprint for probe atoms on a specific lattice site and local surrounding. In each material an axial symmetric EFG was found with a characteristic quadrupole coupling constant ν_Q variing between 250 MHz and 350 MHz. Regarding to the question of lattice location of the In-probes we demonstrate that they occupy the A-site by comparing the experimental results with ab initio DFT calculations using the FP-LAPW+LO method implemented in the WIEN2k package.