Thermodynamic aspects of transition metals doped ZnO

ABSTRACTWe present a thermodynamic study of selected transition metals (TM=Cr, Mn, Fe and Co) solubility in ZnO based on the assessment of available thermodynamic data and ab-initio calculations in the respective TM-Zn-O systems. The ab-initio DFT calculations of enthalpies of formation of the involved phases and the energies of substitution defect (TM-Zn) formation were performed using the full-potential APW+lo technique (WIEN2k code) within GGA+U approximation. The calculated energies of mixed oxides and virtual (unstable) TMO end-members of (Zn,TM)O solid solutions are referred to well established thermodynamic data of binary oxides taken from SGTE database. The assessed thermodynamic data are subsequently used for calculation of phase equilibria and construction of the respective pO2-T-x phase (FactSage software). Whereas the solubility of Mn, Fe, and Co in ZnO is found not to exceed 1 mol% at low temperatures (T<900°C), the homogeneity range is substantially enlarged at elevated temperatures (~10 mol% at the eutectic temperature). By contrast, the solubility of Cr turned out to be negligible in the relevant range of T and pO2.