  The effect of Mg-substitution on the crystal structure of wurtzite ZnO is
presented based on synchrotron X-ray diffraction studies of polycrystalline
Zn1-xMgxO (0 <= x <= 0.15). Increase in Mg concentration results in pronounced
c-axis compression of the hexagonal lattice, and in diminution of the
off-center cation displacement within each tetrahedral ZnO4 unit. Going from
ZnO to Zn0.85Mg0.15O, significant changes in the ionic polarization are
observed (-5.6 to -4.8 uC/cm2), despite only subtle increments in the cell
volume (~0.03 %) and the ab-area dimension (~0.1 %). The optical properties of
the samples have also been characterized and the band gap changes from 3.24 eV
(ZnO) to 3.35 eV (Zn0.85Mg0.15O).
