Formation, Characterization and Magnetic Properties of Some Ternary Al-Cu-M (M = Transition Metal) Quasicrystals Prepared by Conventional Solidification

Abstract

We present a new semi-empirical criterion responsible for the formation and stability of the quasicrystalline state of conventionally solidified ternary Al 80-x Cu 20 M x (M = Ru, Rh, Re, Ir) alloys with x=7.5, 15, 20 at.%. Generally we found that decagonal (D-phase) and icosahedral (I-phase) quasicrystals exist in neighboring composition ranges, when one of the reported criteria examined in terms of average valence electron concentration (e/a) and effective atomic radius ratio (a eff ) is fulfilled. By conventional cooling (dT/dt≈ 103 to 102 Ksec -1) decagonal and icosahedral quasicrystals were formed in all the systems, with the exception of the Al-Cu-Re system, where only crystalline phases were found. In the ternary Al-Cu-Ir system we found large (1–1.3 mm) and stable D- and I-phases. Further on, magnetic susceptibility and magnetization curves of the alloys were investigated in the temperature range from 5 to 300 K and for magnetic fields between -50 kOe ≤ H≤50 kOe . From the resulting magnetization curves the I-Al60Cu20Ru20 alloy shows only paramagnetic behavior in the field range -50 kOe ≤ H≤50 kOe . The other samples show a paramagnetic or a diamagnetic behavior depending on the field intensity. For the samples I-Al72.5Cu20Ru7.5 , I-Al65Cu20Ru15 , D-Al65Cu20Rh15 and D-Al60Cu20Rh20 a paramagnetic behavior was observed in the field range of -1 kOe ≤ H≤1 kOe . Outside this field region a transition to diamagnetism takes place. On the basis of the resulting magnetic susceptibility curves we found that in the range of 20–300 K the magnetic susceptibility is temperature independent for all samples. On the contrary, in the range of 5–20 K the magnetic susceptibility is temperature dependent (the Curie–Weiss law is valid), with the exception of the samples I-Al65Cu20Ru15 , D-Al65Cu20Rh15 , D-Al65Cu20Ir15 and D-Al60Cu20Rh20 . The measured magnetic susceptibility values of conventionally solidified ternary Al-Cu-M (M = Ru, Rh, Re, Ir) alloys lie between the pointed values of icosahedral Al55Cu9.2Li35.8 and Al65Cu20Cr15 alloys.