First-principles energy band calculation of a (Ca²⁺, V⁵⁺)-doped Y₂Ti₂O₇ pigment

Abstract

A first-principles energy band calculation is performed with respect to the V 5+-and (Ca 2+ , V 5+)-doped Y 2 Ti 2 O 7 supercells to elucidate the effect of Ca 2+ doping on the electronic structure and optical properties of a V 5+-doped Y 2 Ti 2 O 7 pigment in the present study. The structural optimization calculation reveals that the theoretical lattice constant of the Y 2 Ti 2 O 7 unit cell slightly increases when compared with that in the experimental data. The forbidden gap at the ¥ point is estimated to be 2.78 eV. On the basis of the density-of-states analysis, the valence band (VB) of Y 2 Ti 2 O 7 mainly comprises the O 2p states and hybridizes with the Ti 3d and Y 4d states. The conduction band (CB) can be divided into two energy regions. The lower CB comprises the Ti 3d states and hybridizes with the O 2p states, whereas the upper CB comprises the Y 4d, Ti 3d, and O 2p states. When Y 2 Ti 2 O 7 is doped with a V atom, the VB width and bandgap are observed to expand by 0.7 and 0.2 eV, respectively, with respect to the pristine Y 2 Ti 2 O 7. Two strongly localized peaks, corresponding to the V 3d states, appear in the bandgap. Further, three strongly localized peaks appear in the bandgap when V 5+-doped Y 2 Ti 2 O 7 is doped with a Ca atom. In the dielectric function calculation of the V 5+-doped Y 2 Ti 2 O 7 , there is broad absorption from the O 2p VB states to the V 3d gap states as well as a VBCB optical transition in the host crystal. When the V 5+-doped Y 2 Ti 2 O 7 is doped with a Ca atom, the distortion of the VO 6 octahedron becomes large, leading to an increment of O 2p state densities near the valence-band maximum of the host. Thus, it is considered the momentum matrix elements between occupied states (O 2p states) and unoccupied states (V 3d states) becomes large in comparison with the case before a Ca doping.

Charge Transfer-Triggered Bi3+Near-Infrared Emission in Y2Ti2O7for Dual-Mode Temperature Sensing

“…For both undoped and Bi-doped samples, the wave-vector k, that is, the momentum is the same for the maximum energy of the valence band and the minimum energy of the conduction band (Figure S7), which indicates the direct band gap of the samples. The PBE-calculated band gap of the YTO is 2.82 eV (22,728 cm –1 ), which agrees well with computed results reported previously. , However, this value is apparently much underestimated compared to any reported experimental results as listed above. It is well known that the GGA-based approximation method tends to underestimate band gaps, especially those of transition metal oxide systems.…”

“…The PBE-calculated band gap of the YTO is 2.82 eV (22,728 cm −1 ), which agrees well with computed results reported previously. 60,61 However, this value is apparently much underestimated compared to any reported experimental results as listed above. It is well known that the GGA-based approximation method tends to underestimate band gaps, especially those of transition metal oxide systems.…”

Effect of M-doping (M = Al, Y, La) on the electronic structure of V-doped ZrO₂: A first-principles study

“…Three types of convergence criteria, that is, the total energy, charge, and force, were used for each self-consistent field-cycle and set to 0.0001 Ry for at least three iterations; 0.001e for the last iteration; and 1.0 In the present study, we assumed that the valences of the doped atoms, M and V, are trivalent and pentavalent, respectively, for the (M,V)-doped ZrO 2 supercells, whereas for the V-doped and M-doped ZrO 2 supercells, we assumed that V and M are tetravalent and trivalent, respectively. 10) As for (M,V)-doped ZrO 2 , there are no reported cases of V valence in ZrO 2 , but it is confirmed that V is present at +4 in ZrO 2 doped only with V. 4)…”

“…Also, we constructed another (M,V)-doped supercell in which the MV distance is longer; however, the total energy of the latter (M,V)-doped supercell increased in comparison with that of the former (M,V)-doped supercell. 10) Therefore, we used the calculation data for the former (M,V)doped supercell in the present study.…”