Si, Ge, or Sn doped hematite (α-Fe2O3) photoanodes show significantly enhanced efficiency
for photo-oxidization
of water. We employed DFT+U to study the doping of
α-Fe2O3 with group IV elements, i.e.,
Si, Ge, and Sn. From the calculated formation energies and chemical
potentials, three key points are concluded. (1) Low oxygen pressure
is favored for doping both substitutional and interstitial dopants.
(2) Substitutional doping of the Fe atom at the lattice site is more
stable than interstitial doping in the octahedral vacancies. (3) Most
interestingly, Ge doping is found to be easiest among the three dopants.
This result contradicts intuition based on atomic size and indicates
that Ge doping should be more efficient than Si and Sn doping in increasing
the charge carrier concentration. Incorporation of the dopants at
the Fe site generates an electron polaron and the dopant with the
+4 valence state by spontaneous transfer of one electron from the
dopant atom to a surrounding Fe atom, according to the analyses of
charge transition energy levels and density of states. We identify
the factors affecting the charge transfer process. The study elucidates
the dopants role in increasing the electrical conductivity of α-Fe2O3 and provides guidelines for designing new efficient
photoanodes.
The projectile landing position has to be determined for its recovery and range in the targeting test. In this paper, a global search method based on the velocity variance is proposed. In order to verify the applicability of this method, simulation analysis within the scope of four million square meters has been conducted in the same array structure of the commonly used linear positioning method, and MATLAB was used to compare and analyze the two methods. The compared simulation results show that the global search method based on the speed of variance has high positioning accuracy and stability, which can meet the needs of impact point location.
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