  The peculiar properties of zinc oxide (ZnO) make this material interesting
for very different applications like light emitting diodes, lasers, and
piezoelectric transducers. Most of these applications are based on epitaxial
ZnO layers grown on suitable substrates, preferably bulk ZnO. Unfortunately the
thermochemical properties of ZnO make the growth of single crystals difficult:
the triple point 1975 deg C., 1.06 bar and the high oxygen fugacity at the
melting point p_O2 = 0.35 bar lead to the prevailing opinion that ZnO crystals
for technical applications can only be grown either by a hydrothermal method or
from "cold crucibles" of solid ZnO. Both methods are known to have significant
drawbacks. Our thermodynamic calculations and crystal growth experiments show,
that in contrast to widely accepted assumptions, ZnO can be molten in metallic
crucibles, if an atmosphere with "self adjusting" p_O2 is used. This new result
is believed to offer new perspectives for ZnO crystal growth by established
standard techniques like the Bridgman method.
