Effect of Mo doping on the microstructures and mechanical properties of ZnO and AZO ceramics

ZnO ceramics should have good mechanical properties to meet their applications in semiconductor industry. Based on experiments and the first principles, the effect of Mo doping on the microstructure and the mechanical properties of ZnO and AZO ceramics were studied, and the model of the effect of Mo doping on ZnO crystal defects was established. The results of the structures and fracture-surface morphology of different systems show that doping Mo atoms is beneficial for ZnO and AZO ceramics to eliminate the lattice defects, promote the grain growth and reduce the porosity at low doping concentration. However, when the doping concentration is too high, the new phase of Zn3Mo2O9 is formed and precipitated in 4MZO crystal. Correspondingly, the lattice distorted of doping systems is so serious that hinders the growth of grains and further affects the mechanical properties. Then, the bilinear stress-strain (sigma-epsilon) relationship was constructed by nanoindentation and finite element method. The results of mechanical properties by nanoindentation experiment and the first-principles simulation show that doping Mo can improve the hardness, elastic modulus, initial yield stress, plastic tangent modulus and creep resistance of ZnO and AZO ceramics. In particular, the mechanical properties of MZO ceramics are significantly improved because of the formation of Mo-O covalent bond between Mo6+ and O2- . In addition, it is worth noting that due to the synergistic and compensation effect of Al and Mo co-doped atoms, which is favor for reducing the lattice strain, improving the resistance to lattice deformation and forming the covalence of MAZO system, the mechanical properties of MAZO ceramics are increased remarkably.