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This study investigates the optical and thermoelectric properties of metallic (cubic TiO, monoclinic TiO, and γ-Ti3O5) and semiconducting (Ti2O3, α-Ti3O5, β-Ti3O5, Ti4O7, and Ti5O9) phases of TinO2n−1, using various functionals including PBE, mBJ, PBE+U, and YS-PBE0. The YS-PBE0 and random phase approximation approaches accurately predict the electronic and optical bandgaps for semiconducting phases, which align well with the experimental data. For the case of semiconducting phases, two significant optical absorption peaks are identified: one in the infrared due to (t2g–eg) interband transitions and another in the ultraviolet due to O-2p to Ti-3d intraband transitions. The semiconducting phases demonstrate impressive Seebeck coefficients (800–1200 μV K−1), driven by large effective mass and flat bands near the Fermi level. The electronic relaxation times are estimated to be 10−14 to 10−16 seconds for TinO2n−1 structures. Although the thermoelectric figure of merit of TinO2n−1 phases is low (<1), there is possibility for improvement through optimizing carrier concentration. These findings suggest that TinO2n−1 can be considered as potential materials for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Titanium suboxides with formula TinO2n−1 have attracted increasing attention owing to their widespread potential applications. Generally, the experimental samples of TinO2n−1 are a mixture of TiO2 suboxides, and the characterization of these phases is not solely possible using x-ray diffraction (XRD). In these cases, Raman modes with XRD can characterize these phases within the samples more precisely. Therefore, the investigation of Raman modes is important. On the other hand, the experimental thermodynamic study predicts that TinO2n−1 can be fabricated with a high index n, where n can take up to 100. So, the Raman modes and thermodynamic properties of these phases, nominally Ti2O3, Ti3O5, and Ti4O7, were investigated within the framework of density functional theory. Comparing the calculated and experimental Raman modes reveals that it is essential to consider the dipole–dipole interaction to reproduce the high Raman modes. Moreover, this electrostatic interaction can be responsible for stabilizing Ti3O5 polymorphs. According to the results, the bipolaronic bonds in Ti3O5 and Ti4O7 lead to a large Born effective charge, which makes these materials plausible for piezoelectric applications. Additionally, thermodynamic calculations reveal that as the n index in TinO2n−1 compounds increases, more stability is achieved at high temperatures, following the experiment. The stability in high temperatures suggests that TinO2n−1 phases can be suitable candidates for thermoelectric devices. [ABSTRACT FROM AUTHOR]

Titanium suboxides with formula TinO2n−1 have attracted increasing attention owing to their widespread potential applications. Generally, the experimental samples of TinO2n−1 are a mixture of TiO2 suboxides, and the characterization of these phases is not solely possible using x-ray diffraction (XRD). In these cases, Raman modes with XRD can characterize these phases within the samples more precisely. Therefore, the investigation of Raman modes is important. On the other hand, the experimental thermodynamic study predicts that TinO2n−1 can be fabricated with a high index n, where n can take up to 100. So, the Raman modes and thermodynamic properties of these phases, nominally Ti2O3, Ti3O5, and Ti4O7, were investigated within the framework of density functional theory. Comparing the calculated and experimental Raman modes reveals that it is essential to consider the dipole–dipole interaction to reproduce the high Raman modes. Moreover, this electrostatic interaction can be responsible for stabilizing Ti3O5 polymorphs. According to the results, the bipolaronic bonds in Ti3O5 and Ti4O7 lead to a large Born effective charge, which makes these materials plausible for piezoelectric applications. Additionally, thermodynamic calculations reveal that as the n index in TinO2n−1 compounds increases, more stability is achieved at high temperatures, following the experiment. The stability in high temperatures suggests that TinO2n−1 phases can be suitable candidates for thermoelectric devices. [ABSTRACT FROM AUTHOR]

In the present work, the electronic and magnetic properties of pure and Cu doped ZnO thin films in the non-polar [10 1 ¯ 0] direction have been investigated in the framework of density functional theory. The bandgap of pure surface was slightly lower than that of the bulk. By doping Cu impurity in the surface, the bandgap decreased relative to that of the pure surface, which is in the visible light region. Furthermore, the spin up and down behaved differently, presenting half-metallic behavior with a net magnetization as large as 1 μ B /cell. These results imply that Cu doped ZnO surface can be applicable in spintronic and optical applications. By including O vacancy in Cu doped surface configurations, the bandgap was decreased leading to the metallic behavior. Furthermore, different magnetization was obtained for each configuration. It states that the presence of O vacancy in Cu doped ZnO surface may affect the induced magnetization in ZnO thin films. [ABSTRACT FROM AUTHOR]