Microwave dielectric properties of Al-doped ZnO powders synthesized by coprecipitation method

Al-doped ZnO (AZO) powders with different Al concentrations were synthesized by coprecipitation method. Crystal structural and dielectric properties of the powders as a function of aluminum doping concentration as well as annealing temperature were investigated. The XRD results reveal that Al atoms are doped into ZnO lattice successfully and all the samples are polycrystalline with a hexagonal wurtzite structure. The real part (ε′) and imaginary part (ε″) of the complex permittivity of the powders were carried out by a vector network analyzer in the microwave frequency range of 8.2-12.4 GHz. The results show that the ε′ and ε″ of the doped ZnO powders increase with the doping content and both of them are higher than that of the pure one. For the AZO powder with 7 mol% Al, both ε′ and ε″ increase firstly and then decrease with increasing annealing temperature.