The effect of Cu doping on the piezoelectric properties of ZnO systems: First-principles calculations

First-principles calculations are performed, revealing a significant enhancement of the piezoelectric properties of wurtzite Zn[Formula: see text]O[Formula: see text] upon the incorporation of a single Cu atom. Research has demonstrated that the piezoelectric constant [Formula: see text] reaches its maximum value at a doping concentration of 1.4% for Cu atoms. The lattice parameters a and c of Zn[Formula: see text]O[Formula: see text] are decreased and the piezoelectric strain coefficient [Formula: see text] is increased by replacing one Cu atom in Zn[Formula: see text]O[Formula: see text]. It is found that elastic softening is the primary factor responsible for the increase of [Formula: see text] in Zn[Formula: see text]Cu₁O[Formula: see text]. By differential charge density analysis, it is found that the covalency between Cu–O bonds is lower than that of Zn–O bonds, and the covalent bonding characteristics are weakened. Bader charge analysis shows that the charge of Cu is higher than that of Zn, indicating a more significant ionic bonding feature than that of Zn. Thus, a weaker covalent and stronger ionic bond are considered to play an essential role in promoting elastic softening for ZnO, which eventually promotes a significant enhancement in piezoelectric properties.