Effect of oxygen vacancy defects on electronic and magnetic properties of copper pyrophosphate material

The effect of oxygen vacancies (VO) on the electronic and magnetic properties of copper pyrophosphate dihydrate Cu2P2O7*2H2O (CuPPD) semiconductors is studied employing the DFT-based ab initio pseudopotential method. Site preference for vacancy formation on the selected oxygen sublattices is analyzed. Investigations revealed that the VO vacancies led to narrow bands of hybridized Cu-3d and O-2p states within the energy gap of perfect CuPPD semiconductors, significantly reducing the gap width from 2.17 eV to 0.19 eV and changing its character from indirect to direct one. Calculations have shown that the vacancies have no significant influence on the ferrimagnetic structure of CuPPD. The magnetic properties are driven by local magnetic moments of Cu atoms pointed oppositely. The oxygen vacancies slightly modify the spin polarization of d-orbitals of Cu atoms neighboring the vacancy, resulting in the non-zero total magnetic moment of 0.19 µB/FU (0.0 µB/FU in perfect CuPPD). The study's main finding, which can be exploited in nanoelectronics, is that the controlled implementation of oxygen vacancies can regulate the energy gap of CuPPD semiconductors.