Underlying Effects of Temperature and Pressure on the Concentration of Carriers and Intrinsic Defects in the Bi2MoO6 Photocatalyst: A Hybrid Density Functional Study

With the visualization of the oxygen chemical potentials (ΔμO) as a function of temperature (T) and oxygen partial pressure (p O2), we transform the dependence of thermodynamical stability and the concentration of intrinsic defects and charge carriers in the Bi2MoO6 photocatalyst on chemical potentials into that on environmental conditions, using the hybrid density functional approach. The Bi2MoO6 stable region is redefined directly and drawn distinctly by T and p O2. From poor oxygen to rich oxygen in the stable region, the self-consistent Fermi level and concentration of electron carriers (n 0) and intrinsic defects under working temperature 300 K, synthesis temperature 700 K, and nonthermodynamic equilibrium conditions quenched from 700 to 300 K are simulated and then visualized as T and p O2, respectively. The values of n 0 more than 1017 cm–3 after quenching, which satisfies the actual photocatalytic performance, just fall outside the conventional experimental conditions (at 300–700 K, 1 atm.) both for only native defects and with A– doping, but they can easily satisfy both the two requirements above while D+ doping. The independence of n 0 equal to 1018 cm–3 on ΔμO within the range from −1.8 to −0.3 eV, deriving from the excitation of D+ doping, is found and does not depend on p O2 and T, bringing great convenience to experimental operation and practical application. Meanwhile, the dominant defect within these experimental conditions is the secondary ionization of the oxygen vacancy with no impurity energy level in the band gap, which hinders the recombination of photogenerated charge carriers. Therefore, the thermodynamic stability and conductivity of materials can be more deeply and clearly explored by visualizing theoretical calculation results as experimental parameters: the temperature and pressure. Adjusting the experimental environment to affect the chemical potential can also play a role in screening out desirable defects and shielding undesirable ones.