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The crystallographic polarity of the noncentrosymmetric material zincite (ZnO) has been determined by a rapid x-ray absorption edge method. The polarity results have been correlated to marked differences in etching behavior and crystal morphology in opposite polar directions of ZnO crystals. These differences are shown to be consistent with the proposed surface bonding model for AII-Bv! compounds. Crystal morphology is shown to be a useful criterion to indicate crystallographic polarity in well-formed wurtzite-type crystals.

The NaCl structures PbS, PbSe, PbTe and SnTe have been found to transform to a Pnma orthorhombic (distorted NaCl) structure under high pressures. Epitaxial growth on rock salt of thin films of normally orthorhombic (Pnma) SnS, SnSe and PbSnS2 induces NaCl structures. There exists a close correlation between the lattice constants of the corresponding NaCl and the orthorhombic polymorphic structures of the Pb and Sn compounds.

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