Inclined net plane faceting observed at Czochralski growth of decagonal AlCoNi quasicrystals

In the ternary Al-Co-Ni system, decagonal quasicrystals occur that have proved thermodynamically stable. Large single crystals can be grown using rather conventional crystal growth techniques from incongruent melts. Decagonal quasicrystals combine two different types of order, periodicity along the 10-fold rotational axis and non-periodic order perpendicular to it, which makes them particularly interesting for solid state physics. Based upon X-ray structure analysis data obtained from AlCoNi single crystals, the question has been discussed whether or not inclined net planes exist that intersect periodic as well as non-periodic directions in these quasicrystals. Several inclined net planes were proposed and ranked with respect to their structure amplitudes. We have studied single crystal growth of large decagonal Al72Co9Ni19 quasicrystals using the Czochralski method from Al-rich melts. The crystal surfaces show a remarkable faceting. Exact angle measurements by optical goniometry revealed that the observed morphological faceting perfectly corresponds to some of the theoretically predicted inclined net planes. Besides the two different decagonal prisms {10000} and {1 0 1¯ 0 0} and the pinacoid {00001} we have found the inclined planes of two decagonal dipyramids {0 0 1¯ 1¯ 1} and {1 0 1¯ 0 2}.