Ab Initio Prediction of the Redox Potentials of 3d Transition Metals Embedded in a Semiconducting Host Lattice

Abstract

Here, we report a theoretical investigation devoted to the ab initio determination of the redox potentials E(D n+ /D n+1 ) of a dopant D in a given host lattice. The knowledge of these potentials is of capital importance to anticipate its attainable oxidation states (versus the synthesis conditions).Hereafter the host lattice has been selected to be the well-known rutile TiO2 compound due to its interest for many applications, the simplicity of its crystal structure and the large number of already collected data. Dopants are 3d transition metals (i.e., V, Mn, Fe, Ni and Cu) substituting titanium atoms. First-principles methods combined to the SCAN functional were used to determine the electronic properties of doped materials considering the supercell approach. The stability of point defects (intrinsic and extrinsic) at different charge states are discussed based on the estimation of their defect formation enthalpies, and the associated charge transition levels are calculated and positioned in the gap of the un-doped material.

Theoretical Calculations Meet Experiment to Explain the Luminescence Properties and the Presence of Defects in m-ZrO2

“…This functional was chosen since it is cost affordable, accurate for structure predictions, and reliable for point defect properties as demonstrated by some of us. 35 The lattice parameters of the ideal m-ZrO 69 The band gap was estimated at 4.14 eV, while a HSE06 70 approach gave 5.28 eV close to already reported GW 0 71 (5.34 eV), HSE 40 (5.22 eV), and EELS 72 (5.3 eV) data. For a HSE06@SCAN calculation (i.e., HSE06 band gap estimated on the fully optimized SCAN structure), we found 5.23 eV in great agreement with the HSE06 value.…”

“…Here, we considered the SCAN functional to estimate defect formation enthalpies (DFEs) for intrinsic defects and Ti impurities. This functional was chosen since it is cost affordable, accurate for structure predictions, and reliable for point defect properties as demonstrated by some of us . The lattice parameters of the ideal m -ZrO 2 unit cell were calculated at a = 5.146 Å, b = 5.226 Å, c = 5.315 Å, and β = 99.32°, close to the experimental values ( a = 5.14422(4) Å, b = 5.20969(5) Å, c = 5.31120(5) Å, and β = 99.220(1)°) .…”

“…This functional was chosen since it is cost affordable, accurate for structure predictions and reliable for point defect properties as demonstrated by some of us. 35 The lattice parameters of the ideal m-ZrO with Ti located at the Zr site (T i Zr ) and at the interstitial position (T i i ).…”

“…From the theoretical side, Density Functional Theory (DFT) is usually used for inorganic solids in optics to determine band gaps, identify electronic transitions at work in a given material, and get access to the complex refractive indexes. More recently, DFT has been employed to provide information on charge transition levels within the band gap, − enabling one to characterize the presence and the nature of defects in the studied structure. To our knowledge, such simulations have been reported for (only) intrinsic point defects in m -ZrO 2 . ,− Consequently, this prompted us to revisit in-depth the impact of defects ( i.e.…”

First-principles calculations to identify key native point defects in Sr4Al14O25

“…Indeed, ab initio methods can be used to estimate the formation energy of point defects, and to determine their impact on the electronic structure of the ideal material. [20][21][22][23][24][25][26][27][28][29][30][31] Surprisingly, from our knowledge, such kind of simulations have not been reported for the Sr 4 Al 14 O 25 compound yet. Herein, we propose to fill this lack by characterizing more than 30 possible intrinsic point defects in this material and to identify the prominent expected ones versus specific synthesis conditions.…”