Piezoelectric properties of monolayer II-VI group oxides by first-principles calculations

Piezoelectric properties of group II-VI oxide structures is carried out by first principles methods. Piezoelectric effect is the ability of the certain materials to generate an electric charge in response to applied mechanical stress, and it is also reversible. Two-dimensional IIA/IIB-VI group oxides are expected to have great potential due to their non-centrosymmetric structure and intrinsic large band gaps. PBE formulation and HSE06 hybrid functionals were used to get realistic forbidden bandgap values. Density functional theory-based first-principles calculations (DFT and DFPT) are used to investigate the piezoelectric stress, e11, and strain, d11, coefficients of monolayer IIA/IIB-VI group oxides (MO where M=Be, Mg, Ca, Sr, Ba, Zn, and Cd). We predicted that 2D II-VI family compounds exhibit highly promising piezoelectric properties. BeO has the highest e11 and the BaO has the highest d11 relaxed-ion coefficients. All piezoelectricity calculation results give close values for the CaO structure. Calculation results show increasing trend for relaxed ion piezoelectric coefficients for IIA group and decreasing trend for IIB group, according to row number of the atoms. Our calculations reveal that II-VI family oxide structures are strong candidates for future atomically thin piezoelectric applications.