New icosahedral and approximant phases in Al-Rh-Si system

An icosahedral phase (i phase) and its crystal approximant of the 2/1 cubic type ( a = 1.993 nm) have been found to form in the Al-Rh-Si system, in addition to a 1/0 cubic approximant phase ( a = 0.767 nm) previously reported. X-ray and electron diffraction patterns of the i phase and approximant phases have been analysed in terms of the hyperspace structural description in quasi-crystallography. While the i phase is metastable, the 2/1 cubic approximant phase is found to be stable. Single crystals of the 2/1 cubic phase of about 0.3 mm 3 in size have been grown by solidification following arc melting. The single crystals have cubic morphology with flat facets.