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 3 6 O 3 6 upon the incorporation of a single Cu atom. Research has demonstrated that the piezoelectric constant d 3 3 reaches its maximum value at a doping concentration of 1.4% for Cu atoms. The lattice parameters a and c of Zn 3 6 O 3 6 are decreased and the piezoelectric strain coefficient d 3 3 is increased by replacing one Cu atom in Zn 3 6 O 3 6 . It is found that elastic softening is the primary factor responsible for the increase of d 3 3 in Zn 3 5 Cu1O 3 6 . 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. [ABSTRACT FROM AUTHOR]