Local compositions and structures of ${\text{Zn}}_{1-x}{\text{Mg}}_x\text{O}$ alloys have been investigated by Raman and solid-state ${}^{67}\text{Z}\text{n}/{}^{25}\text{M}\text{g}$ nuclear-magnetic-resonance (NMR) spectroscopies and by neutron pair-distribution-function (PDF) analyses. The $E_2^{\text{low}}$ and $E_2^{\text{high}}$ Raman modes of ${\text{Zn}}_{1-x}{\text{Mg}}_x\text{O}$ display Gaussian- and Lorentzian-type profiles, respectively. At higher Mg substitutions, both modes become broader, while their peak positions shift in opposite directions. The evolution of Raman spectra from ${\text{Zn}}_{1-x}{\text{Mg}}_x\text{O}$ solid solutions is discussed in terms of lattice deformation associated with the distinct coordination preferences of Zn and Mg. Solid-state magic-angle-spinning (MAS) NMR studies suggest that the local electronic environments of ${}^{67}\text{Z}\text{n}$ in ZnO are only weakly modified by the 15% substitution of Mg for Zn. ${}^{25}\text{M}\text{g}$ MAS spectra of ${\text{Zn}}_{0.85}{\text{Mg}}_{0.15}\text{O}$ show an unusual upfield shift, demonstrating the prominent shielding ability of Zn in the nearby oxidic coordination sphere. Neutron PDF analyses of ${\text{Zn}}_{0.875}{\text{Mg}}_{0.125}\text{O}$ using a $2\times 2\times 1$ supercell corresponding to ${\text{Zn}}_7{\text{MgO}}_8$ suggest that the mean local geometry of ${\text{MgO}}_4$ fragments concurs with previous density-functional-theory-based structural relaxations of hexagonal wurtzite MgO. ${\text{MgO}}_4$ tetrahedra are markedly compressed along their $c$ axes and are smaller in volume than ${\text{ZnO}}_4$ units by $\approx 6\%$. Mg atoms in ${\text{Zn}}_{1-x}{\text{Mg}}_x\text{O}$ have a shorter bond to the $c$-axial oxygen atom than to the three lateral oxygen atoms, which is distinct from the coordination of Zn. The precise structure, both local and average, of ${\text{Zn}}_{0.875}{\text{Mg}}_{0.125}\text{O}$ obtained from time-of-flight total neutron scattering supports the view that Mg substitution in ZnO results in increased total spontaneous polarization.

• Received 5 August 2008

DOI:https://doi.org/10.1103/PhysRevB.78.195205