Westfälische Wilhelms-Universität Münster

- Fachbereich Physik -

SONDERKOLLOQUIUM

Montag, 18. November 2002

Dr. Wolfgang Sprengel

Institut für Theoretische und Angewandte Physik, Universität Stuttgart

Point Defects and Phase Transformations in Complex Solids: Quasicrystals

Positron annihilation studies of vacancies, atomic processes and phase transformations in quasicrystals will be reported, where icosahedral AlPdMn, ZnMgHo, decagonal AlNiCo and related approximants have been used as role models for quasicrystalline structures, i.e., structurally complex alloy phases. Structural vacancies are present in all investigated quasicrystals. Formation and migration of thermal vacancies at high temperatures have been investigated by positron lifetime spectroscopy as well as by the coincident Doppler broadening technique. The latter technique has been proven to be a powerful approach to study the formation of lattice vacancies even under the condition of positron saturation trapping as it takes advantage of the change of the local chemical environment of the trapping site. Coincident Doppler broadening measurements have also successfully been applied to study order-disorder phase transformations in d-AlNiCo at high temperatures.

Ort: Wilhelm-Klemm-Str. 10, Seminarraum 619

Zeit: 15 Uhr s.t.

Einladender: H. Mehrer