Regensburg 2000 – scientific programme

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M: Metallphysik

M 13: Elektronische Strukturen und Eigenschaften

M 13.3: Talk

Thursday, March 30, 2000, 13:00–13:15, H6

Ordering in Cu-Zn-Al alloys — •V. Crisan¹, H. Ebert¹, P. Entel², and H. Akai³ — ¹Institut für Physikalische Chemie, Universität München, Butenandtstraße. 5–13, 81377 München — ²Theoretische Physik, Gerhard-Mercator Universität, Lotharstraße 1, 47048 Duisburg — ³Department of Physics, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan

The ordering of the first and next-nearest neighbor atoms in Cu-Zn-Al alloys is studied in the concentration range, where martensitic transitions occur, by using a KKR-CPA method. Because of the non diffusive character of the martensitic transition only the parent phases are studied. The transition from the disordered A2 phase to the ordered B2 phase was calculated by using an order parameter which defines the occupancy of one of the bcc lattice sites. From the total energy data it resulted that the system is more stable in the B2 structure for all compositions, which is in agreement with experimental data. Also no important changes of the lattice parameters with ordering was observed. In addition we found that the ordering in the second-nearest neighbors leads to very unstable atomic arrangements. For the particular compound Cu₇₀Zn₁₅Al₁₅, which shows rubber-like behavior, a selective replacement of the Cu atoms by Zn atoms leads to a metastable L2₁ structure, which actually could be related to the formation of martensite. The impact of ordering on the density of states, Fermi surface and Bloch spectral function was also investigated.