Evolution of local structures in polycrystalline Zn1−xMgxO (0⩽x⩽0.15) studied by Raman spectroscopy and synchrotron x-ray pair-distribution-function analysis

Abstract

The local structures of ${\mathrm{Zn}}_{1-x}{\mathrm{Mg}}_x\mathrm{O}$ alloys have been studied by Raman spectroscopy and by synchrotron x-ray pair-distribution-function (PDF) analysis. Within the solid solution range $(0⩽x⩽0.15)$ of ${\mathrm{Zn}}_{1-x}{\mathrm{Mg}}_x\mathrm{O}$, the wurtzite framework is maintained with Mg homogeneously distributed throughout the wurtzite lattice. The $E_2^{\text{high}}$ Raman line of ${\mathrm{Zn}}_{1-x}{\mathrm{Mg}}_x\mathrm{O}$ displays systematic changes in response to the evolution of the crystal lattice upon the Mg substitution. The redshift and broadening of the $E_2^{\text{high}}$ mode are explained by the expansion of hexagonal $ab$ dimensions and compositional disorder of $\mathrm{Zn}∕\mathrm{Mg}$, respectively. Synchrotron x-ray PDF analyses of ${\mathrm{Zn}}_{1-x}{\mathrm{Mg}}_x\mathrm{O}$ reveal that the Mg atoms have a slightly reduced wurtzite parameter $u$ and more regular tetrahedral bond distances than the Zn atoms. For both Zn and Mg, the internal tetrahedral geometries are independent of the alloy composition.