i-Al-Cu-Fe-Co Quasicrystals with High Co Content.*

We developed a conceptual phase diagram of Al-Cu-(Fe+Co) quasicrystals and a method to grow stable Al-Cu-Fe-Co icosahedral single-grain quasicrystals with high cobalt content. Our original three-stage process includes (i) heating up a correct mixture of Al, Cu, Fe, and Co elements above the temperature of liquidus; (ii) fast cooling of the melt down to the quasicrystalline single phase region with rate of ~250 F/h to prevent growing of non-quasicrystalline phases in the melt; and (iii) slow cooling down with rate of ~3.5 F/h to grow large (mm-size) single-grain quasicrystals. The chemical composition of the grown quasicrystals was determined by the energy-dispersive X-ray analysis and inductively coupled plasma mass spectrometry and showed that Co substituted up to 23 % of Fe atoms. Powder XRD and selected area electron diffraction were carried out for the phase identification. Temperature dependencies of the electrical resistance were performed on oriented samples in the form of rectangular parallelepipeds by the four-probe method in the temperature range of 1.4 K - 300 K.