Promoting defect formation and microwave loss properties in δ-MnO2 via Co doping: A first-principles study

The delta-MnO2 has a layered structure and is expected to be a good absorbing material. Here, CASTEP was used for a theoretical study of the microwave absorption properties of delta-MnO2 with defects (interstitial and substitutional cobalt atoms, vacancies). The results show that by analyzing the density of states (DOS) and partial density of states (PDOS), the defects change the charge distribution and increase the magnetic moment (increased by about 19 orders of magnitude). The bond length increased from 1.979 angstrom to 1.980 angstrom after substitutional defects formed to enhance the displacement polarizability. The changes in the charge distribution increase the atomic polarizability. The presence of crystal defects enhances both the magnetic loss and dielectric loss. In addition, the calculated defect formation energies show that the Co atoms tend to form interstitial atoms in MnO2 (-16.90 eV), and the oxygen vacancy defects (-0.77 eV) are more easily formed than the manganese vacancy (33.14 eV). (C) 2017 Elsevier B.V. All rights reserved.