Co-doped ZnO: synthesis and structural, electrical and optical properties

Abstract

This paper reports the synthesis, crystal structure and electrical conductivity properties of Co-doped ZnO powders (in the range of 0.25–15 mol%). I-phase samples, which were indexed as single phase with a hexagonal (wurtzite) structure in the Co-doped ZnO system, were determined by X-ray diffraction. The solubility limit of Co ions in the ZnO structure was found to be 15 mol% at after heating at 950 °C. The impurity phase was determined to be Co3O4 at lower temperatures than 950 °C. The research focused on single I-phase samples which were synthesized at 950 °C. For I-phase samples (after heating at 950 °C), the lattice parameters a and c decreased with increasing Co concentration. Electrical conductivity of undoped ZnO and 15 mol% Co-doped ZnO (after heating at 950 °C) were found to be 7.8*10−7 and 1.05*10−4 Ω−1 cm−1, respectively, at 25 °C and 1.15 and 37.15 Ω−1 cm−1, respectively, at 950 °C. Thus, it appears that electrical conductivity slightly increases with Co doping. Also, activation energy of the all I-phase samples (after heating at 950 °C) was calculated and the values were found to be range from 0.774 to 1.201 eV. UV/vis absorption spectras of undoped and the all I-phase samples (after heating at 950 °C) were recorded and optical band gap values were found to be between 3.351 and 3.416 eV.