Ti 3d States Research Articles

Common anion rule in oxide heterointerfaces: Experimental verification by in situ photoemission spectroscopy

The band alignment at the interface is one of the fundamental parameters for designing electronic devices and artificial functional materials. However, there is no firmly established guideline for oxide heterostructures, limiting the functional design of oxide heterostructures. Here, we provide spectral evidence that the band diagram of oxide heterointerfaces is well described by the Zhong and Hansmann scheme based on the common anion rule [Z. Zhong and P. Hansmann, Phys. Rev. X 7, 011023 (2017)]. By utilizing the elemental selectivity of Ti 2p–3d resonant photoemission for the Ti 3d state near the Fermi level, we directly visualize the presence or absence of charge transfer from the overlayer films to SrTiO3 in prototypical heterointerfaces of SrVO3/SrTiO3 and SrNbO3/SrTiO3. It is found that the charge transfer occurs in SrNbO3/SrTiO3 but not in SrVO3/SrTiO3, as predicted by the Zhong and Hansmann scheme, indicating that the presence or absence, as well as the sign and amount, of interfacial charge transfer is predicted by this scheme. Our findings provide guidelines for designing and controlling the functionalities in oxide nanostructures.

A comparative study of DFT and experimental investigations for exploring the effect of Ti doping on the electronic, structural, and optical properties of Cu2O

The current study presents the influence of Ti doping on the electronic, structural, and optical properties of Cu2O. The investigation employs a comparative approach, integrating theoretical calculations using density functional theory and experimental outcomes. Density of states spectra depicted the maximum contribution of Cu-d and O-p in the valence band, whereas Ti-d states filled the conduction band. Structural changes induced by Ti doping, including variations in peak intensity, crystallite size, and defects were examined in detail by X-ray diffraction analysis. The field emission scanning electron microscopy described grain morphology significantly changing upon Ti doping. Optical properties were scrutinized to determine variations in optical parameters. For both un-doped and Ti-doped Cu2O, the experimentally measured band gap was found to be decreased, ranging from 2.05 eV to 1.69 eV. The comparative studies enable a valuable understanding of the effectiveness of Ti doping in modifying the properties of Cu2O.

Band-gap tuning in Mn-doped Er2Ti2O7: Insight from the experimental and theoretical approach

We report the studies of electronic and optical properties of Er2Ti2−xMnxO7 (x = 0, 0.1, & 0.2) through combined theoretical insights from density functional theory (DFT) calculations and experimental approaches, including ultraviolet-visible absorption, photoluminescence emission spectroscopy, and Raman spectroscopy. For quantitatively correct optical bandgaps through DFT calculations, we considered the LDA-1/2 technique for the exchange-correlation interactions. The energy bandgap values obtained using theoretical formulations are in close accordance with the experimental results. The bandgap value obtained using the LDA-1/2 approach indicates the insulated ground state of the Er2Ti2−xMnxO7 (x = 0, 0.1, & 0.2) system. The band gap value obtained experimentally reduces from 3.82 eV to 2.45 eV as the level of Mn doping increases from 0 to 0.2. This reduction in the experimental band gap is attributed to the fact that inclusion of Mn atoms into the crystal lattice alters the electronic structure of the system. Substituting the Mn atom introduces additional electronic states within the band structure, leading to a modification of the band gap. Crystallographic data indicates that inclusion of Mn reduces the Ti-O bond length as in indicated in the table which reduces to 1.939(0) Å for x = 0.2 from 1.947(0) Å for x = 0. This results in the reduction of the extent of hybridization between O-2p and Ti-3d states, thereby reducing the band gap.

Comprehensive investigation of Li-based novel quaternary Heusler LiTiPdZ (Z = Al, Ga, In) compounds for thermoelectric performance

In the present article, we used Density Functional Theory and the Boltzmann transport equation to study the structural, electronic, and thermoelectric (TE) properties along with phonon dynamics of recently discovered LiTiPdZ (Z = Al, Ga, In) quaternary Heusler (QH) compounds. We applied generalized gradient approximations (GGA) for band structure and density of states (DOS) calculations. Comprehensive investigations of electronic structure reveal that an indirect band gap of 0.77 eV, 0.793 eV and 0.611 eV for LiTiPdAl, LiTiPdGa, and LiTiPdIn, is there reflecting the semiconducting nature of these compounds. We find that Pd-4d states contribute to the conduction band DOS while Ti-3d states contribute significantly to DOS near Fermi energy (EF) in both valence and conduction band. Phonon dispersion spectra show that all the studied compounds are dynamically stable, as obtained frequency is only in positive range. We have calculated thermoelectric properties up to a fairly high temperature (1600 K), to check the compatibility of these compounds for high temperature TE application. A high value of ZT (∼0.60 1600K) proposes these compounds as potential candidates for high temperature TE applications.

First principles predictions of structural, electronic and topological properties of two-dimensional Janus Ti2N2XI (X = Br, Cl) structures.

Motivated by the report of the giant Rashba effect in ternary layered compounds BiTeX, we consider two Janus structured compounds Ti2N2XI (X = Br, Cl) of the same ternary family exhibiting a 1 : 1 : 1 stoichiometric ratio. Broken inversion symmetry in the Janus structure, together with its unique electronic structure exhibiting anti-crossing states formed between Ti-d states and strong spin-orbit coupled I-p states, generates large Rashba cofficients of 2-3 eV Å for these compounds, classifying them as strong Rashba compounds. The anti-crossing features of the first-principles calculated electronic structure also result in non-trivial topology, combining two quantum phenomena - Rashba effect and non-trivial topology - in the same materials. This makes Janus TiNI compounds candidate materials for two-dimensional composite quantum materials. The situation becomes further promising by the fact that the properties are found to exhibit extreme sensitivity and tunability upon application of uniaxial strain.

Janus layers and electronic structure of 1T-(TiSeS)2.

TiS2-TiSe2 is one of the most studied titanium based solid solution systems. However, so far, all research on it has only focused on its disordered phase. Here, we systematically investigate its ordered phases. Using a structure search method based on the particle swarm optimization (CALYPSO) algorithm, we identify TiSeS-156 and discover a new structure (1T-(TiSeS)2). Based on first principles theory, their phonon spectra, formation energy, mechanical, electronic, thermal, and optical properties, as well as chemical bond analysis and synthetic pathways, have been investigated. The primitive cell of TiSeS-156 has three atoms and has a space group of P3m1 (no. 156). 1T-(TiSeS)2 has six atoms and has P3̄m1 symmetry (no. 164). TiSeS-156 and 1T-(TiSeS)2 are constructed by stacking the S-Ti-Se Janus layer materials. TiSeS-156 and 1T-(TiSeS)2 are narrow-gap semiconductors. The localized nature of the Ti(3d) states of TiSeS-156 and 1T-(TiSeS)2 leads to their semiconductor properties. 1T-(TiSeS)2 and TiSeS-156 have very similar mechanical, electronic, thermal, and optical properties of 1T-TiS2 and 1T-TiSe2, and are members of the 2D hexagonal lattice transition metal dichalcogenide layered material family. However, compared with 1T-TiS2 and 1T-TiSe2, TiSeS-156 and 1T-(TiSeS)2 have a wider range of potential applications, such as photovoltaic devices and photocatalysis, due to their S-Ti-Se Janus layer structure. They also provide a pathway for the preparation of Janus TiSeS monolayer and multi-layer materials. Moreover, our findings provide crucial insights for understanding the rich and complex crystal structures of the TiS2-TiSe2 system, which have broad implications for further exploration of this class of promising materials.

Enhancement of energy storage performance in lead‐free relaxor ferroelectric ceramics via band structure engineering

AbstractDielectric capacitors with excellent energy storage performance (ESP) are in great demand in the power electronics industry due to their high power density. For the dielectric materials, the dielectric breakdown strength (BDS) is the key factor to improve ESP, which is the focus and bottleneck of current research, especially in the relaxor ferroelectric (RFE) materials with already low residual polarization (Pr). Here, we stimulate the ESP of the BaTiO3 (BT)‐based RFE ceramics by band structure engineering. The Ta element is selected to enhance the band gap of doped ceramics, occupying Ti‐site in supercell of BT and optimizing the bonds length of Ti‐O bond to increase the energy band of Ti 3d states. In this way, the band gap of the doped ceramics is efficiently enhanced from 1.8 eV to 2.22 eV resulting in the large BDS. Prospectively, combined with the advantage of fine grain size, the highest recoverable energy storage density (Wrec) of 2.85 J/cm3 is obtained at 350 kV/cm and the ultra‐high energy efficiency (η) of 95.26% is found at 200 kV/cm. Our work reveals the relationship between elements doping in B‐site and band structure, being expected to benefit for designing energy storage materials.

Layered–Control Approach to Tune The Mobility of Perovskite SrTiO3: A Density Functional Theory Prospects

The advancement of epitaxial technology has enabled the simulation of oxide heterostructures (HS) with unique interfacial material characteristics not found in bulk materials. Recent discoveries of emergent phenomena of definite oxide interfaces have attracted much attention to oxide HS. This work explored the possibility of tuning the electron mobility of SrTiO3 (STO) through CaSnO3/SrTiO3 and ZnSnO3/SrTiO3 HSs, based on density functional theory (DFT). Own to the Sn–5s states of CSO and ZSO with more substantial band dispersion than Ti–3d states of STO, near conduction band minimum (CBM), our simulated results suggest that the bandgaps of CSO/STO (0.502 eV) and ZSO/STO (0.349 eV) HS systems are much smaller than bulk STO (1.802 eV). The effective electron masses also show much smaller values (0.31 and 0.40 m0) and (0.38 and 0.52 m0) for (CSO)7/(STO)4 and (ZSO)1/(STO)4 for HS systems compared to bulk STO (7.03 and 0.94 m0) along Γ–X and Γ–M direction. The bandgap and effective electron masses results suggest that the bandgap of STO can be well controlled and tuned by the thin film layer numbers of CSO and ZSO with better electron transportability.

Enhanced quantum capacitance in Ti, V, Cr, Fe, Ga, Ge, Se, and Br doped arsenene: A first principles investigation

The present work systematically studied the quantum capacitance in 3d (Ti, V, Cr, Fe) and 3p (Ga, Ge, Se, Br) doped Arsenene using first-principles calculation. The calculated negative formation energy (EF) advocates the feasibility of such doping, with a large EF for 3d-Arsenene. Among the dopants, Ti was strongly embedded within the vicinity of the thinned monolayer. The HOMO-LUMO analysis confirms a strong interaction between the Ti-3d state and the Arsenene 4p-state. More importantly, semiconducting states resulted on Ti/Ga/Ge/Br doping, whereas metallic states took place from V/Cr/Fe/Se doping. Projected density of state (PDOS) also advocates these observations and predicts the 3d-state to play an important role in calculating the quantum capacitance (CQ) of 3d-Arsenene. It is found that 3d/4p doping significantly enhanced the quantum capacitances (CQ)/surface charges (Q) of Arsenene. Among 3d and 4p doping, Cr-Arsenene and Se-Arsenene, respectively, have the highest CQ of 345 µF/cm2 and 176 µF/cm2 in the positive and negative bias region, respectively. The finding recommends Cr and Se-doped Arsenene for asymmetric supercapacitors as anode and cathode materials, respectively. Also, Ti/V/Fe/Ga/Ge/Br-Arsenene show enhanced CQ and surface charge (Q), making them suitable for supercapacitor applications.

Structural, electronic and optical properties of ZnO and TiO2 nanoparticles for wastewater treatment: A first-principles study

Water quality deteriorates when industrial and human activities increase. This means that toxins must be removed from industrial and domestic wastewater. In the context of nanotechnology, anchoring TiO2 and ZnO nanoparticles on clay has also been shown to be potential sequesters and has been examined for wastewater treatment. This paper presents a thorough investigation of the structural, electronic, and optical featuresof ZnO & TiO2 nanoparticles using the GGA-PBE functional within the framework of density functional theory (DFT). For ZnO and TiO2 nanoparticles, there is excellent agreement between the calculated lattice parameters and the findings of the experiments. Electronic structure calculations confirm that both ZnO and TiO2 are semiconducting in nature. The density of states calculation reveals that the conduction band in TiO2 is primarily derived from hybridization between Ti-3d states and O-2p states, whereas the valence band is derived from mixing between Ti-3d and O-2p states. Further, ZnO, O-2p, andZn-3d states, primarily contributed to the valence band, while Zn-4 s and Zn-3p states mainly contributed to the conduction band. Since drinking water disinfection processes frequently involve ultraviolet (UV) absorption based advanced oxidation process. Investigations of the optical properties of these two materials suggest that ZnO and TiO2 show great potential as strong UV-absorbing and photocatalytic materials, and can be utilized as microbial disinfectants during wastewater treatment.

A comprehensive DFT evaluation of catalytic and optoelectronic properties of BaTiO3 polymorphs

BaTiO3 exhibits promising photocatalytic characteristics and has the potential to be employed in photocatalytic water splitting and pollutant degradation. Herein, we have investigated the structural, electronic, and optical properties of BaTiO3 in the framework of density functional theory (DFT). The obtained results are found to be consistent with theoretical results. However, using hybrid HSE06 functional, the calculated bandgap values are 3.254, 3.894, 3.694, 3.519, and 3.388 eV corresponding to cubic, rhombohedral, orthorhombic, tetragonal, and hexagonal phase of BaTiO3 polymorphs. This is the first time a DFT calculation touched over the experimental bandgap values of BaTiO3 polymorphs.Electronic band structure analysis revealed that all the BaTiO3 polymorphs exhibit semiconducting character with indirect bandgap except hexagonal structure which possesses direct bandgap. The density of states (DOS), Mulliken bond analysis and charge density distribution indicates considerable hybridization between O-2p and Ti-3d states caused to the formation of upper valence band (VB) and lower conduction band (CB). The wide bandgap and suitable redox potential of BaTiO3 polymorphs will be effective for water splitting as well as breakdown organic contaminants under UV–vis irradiation. The lower electron effective mass of the polymorphs indicates higher electrical conductivity. The energy dependent optical parameters show close agreement with the underlying electronic band structure. The high absorptivity, lower reflectivity and optical anisotropy (orthorhombic and tetragonal) of the polymorphs suggested that these could be a potential candidate for UV based optical device applications as well as to design wave guides, dielectric condensers and optical display devices.

The structural, mechanical and electronic properties of Ti-Al-based compounds by first-principles calculations.

The first-principles calculations with density functional theory were performed to investigate the effects of transition metal elements (Mo, Cu, Fe, Ni and Nb) on the physical properties of the Ti-Al-based compounds. Our optimized crystal parameters are in good agreement with the previous theoretical and experimental values. The mechanical stability is verified by the independent elastic constants. The B/G and Poisson's ratio ν both show that Al6TiMo is brittle, while other compounds exhibit ductility. The values of compression anisotropy of the compounds are small, but the shear anisotropy of AlCu2Ti and AlNi2Ti is much more intense than that of other compounds. The anisotropy in elastic properties of AlFe2Ti and AlNbTi2 is smaller than that of the others. It can be seen that the capacity to compress along c-axis is smaller than that along a-axis and b-axis for AlNbTi2. For AlNbTi2, the anisotropy of the bulk modulus along a-axis relative to b-axis is more insignificant than that along c-axis relative to b-axis. The hardness and Debye temperature verify that AlFe2Ti has the greatest resistance to the plastic deformation and more intense inter-atomic bonding force, respectively. Band structures and DOS are used to investigate the electronic properties. The band structures without band gaps show that these ternary Ti-Al-based compounds are conductors. DOS shows the interactions between elements and gives the bond properties. Density of states and charge density both show the strong covalent properties of AlFe2Ti by the hybridization between Fe-3d and Ti-3d states.

Prediction of phonon-mediated superconductivity in new Ti-based M_2AX phases

A high-throughput computational method is used to predict 39 new superconductors in the Ti-based M_2AX phases, and the best candidates are then studied in more detail using density functional theory electron–phonon coupling calculations. The detailed calculations agree with the simple predictions, and Ti_2AlX (X: B, C and N) materials are predicted to have higher values of T_c than any currently known hexagonal M_2AX phases. The electronic states at the Fermi level are dominated by the Ti 3d states. The choice of X (X: B, C and N) has a significant impact on the electronic density of states but not on the phonon characteristics. The electron–phonon coupling parameter for Ti_2AlX (X: B, C and N) was determined to be 0.685, 0.743 and 0.775 with a predicted T_c of 7.8 K, 10.8 K and 13.0 K, respectively.

First principles study on optical and thermal properties of BaTiS3

Electronic, optical and thermal properties of hexagonal perovskite structure of BaTiS3, are studied, by means of the density functional theory (DFT) implemented on CASTEP, Material Studio, computer program. The data is optimized with generalized gradient approximation (GGA) and exchange correlation function called local density approximation (LDA), within the Broyden-Goldfarb-Shanno (BFGS) scheme of minimization and Koelling-Harmon relativistic treatment. Structure of BaTiS3, which we studied, crystallizes in the space group P63/mmc. Our results for structural, electronic and thermal properties of BaTiS3 are reported for the first time in comparison with experimental and other theoretical results wherever these are available. The electronic band structure reveals p-type semiconducting behavior and major contribution occurs from S-3p orbitals in Valence band and the conduction band is basically constructed from Ti-3d states. Reflectivity of BaTiS3 is also founded to be higher within visible and in ultraviolet region up to 25 eV, which indicates the potentiality of this material to be utilized as a jacket to elude solar heating. Coefficient of absorption spectra of BaTiS3 reveals the conducting nature of this material. The negative values of ε1(ω) is additionally observed,which is obvious indication of Drude like behavior seen in metals. Index of refraction is relatively higher within the infrared section and steadily lowered within the visible and ultraviolet frequency region. Analysis for conductivity also favors the photoconductivity with small photon energy. Thermo dynamical properties reported for the first time with Debye temperature of 1000 K.

Effects of Hubbard U correction on the structural and electronic properties of rutile, anatase and brookite TiO2

In this work, the first-principles calculations using density functional theory (DFT) was applied to calculate the structural and electronic properties of anatase, rutile and brookite TiO2 phases. The effects of Hubbard U correction on the structural and electronic properties of rutile, anatase TiO2 were explored using the local density approximation (LDA) and generalized gradient approximation (GGA) for Perdew-Burke-Ernzerhof (PBE) and Perdew-Burke-Ernzerhof for solids (PBEsol) method by applying Hubbard corrections Ud in Ti 3d states and Up in O 2p states. There are changes in the structural parameters caused by the Hubbard U correction in Ti d states and O p states. The best agreement of U values to improve the electronic band gap of rutile was found at Ud = 3.0 eV and Up = 7.0 eV from LDA, Ud = 2.0 eV, Up = 6.0 eV from GGA-PBEsol for anatase and Ud = 3.0 eV and Up = 4.0 eV for brookite using GGA-PBEsol. The combination of both Ud and Up correction terms managed to widen the band gap of rutile, anatase and brookite TiO2 which is close to the experimental value.

Photocatalytic and Optical Performances of CeO2 by Substitution of Titanium

In this contribution, density functional theory-based calculations have been carried out to assess the electronic, photocatalytic and optical properties of Ce1-xTixO2 system. Ti incorporation leads to a decrease of Ce 4f states and enhancement of Ti 3d states in the bottom of conduction band. Furthermore, it was found that doping ceria with Ti-like transition metals could evidently shift the absorption of pure CeO2 towards higher wavelength range. These findings can provide some new insights for designing CeO2-based photocatalysts with high photocatalytic performance. To the best of our knowledge, this investigation calculates Mullikan’s charge transfer of Ce1-xTixO2 system for the first time. Charge transfer reveals an ionic bond between Ce or Ti and O, and covalent bonds between Ce and Ti atoms in the studies systems.

Effect of Ti incorporation on the electronic structure and optical properties of MoS2 (a first principle study)

The novelty of the Molybdenum disulfide (MoS2) emerges owing to its opportunity to replace graphene and Si technology. In order to explore the great potential of the MoS2 in current technology, its doping with the titanium (Ti) is performed using the first principle calculations. The exchange and correlation effects are approximated using the Perdew–Burke–Ernzerhof, generalized gradient approximation (PBE-GGA) as employed in the Wien2k code. The Ti atoms substitute the Mo atoms and different concentrations (3.7%, 5.55%, 12.5%) are computationally realized in the current study. A review of the partial density of states (PDOS) and total density of states (TDOS) suggest a remarkable contribution of Ti 3d-states while these dopant states appreciably participate in tuning the electronic properties of Ti doped MoS2 (Ti:MoS2). A blueshift in the absorption spectrum is noticed along with increase in Ti concentrations which leads to its potential uses in the high energy visible optoelectronic applications. Moreover, an increase in dielectric constant and refractive index is observed which further extends the uses of the proposed material (Ti:MoS2) in the fields of photonic, photodetectors, optics, and photosensing applications.

Metallization of TiO2(110) with Gold and Lithium

Gold and lithium have been deposited on clean, stoichiometric TiO2(110) to study the evolution of the electronic structure of the surface. For thermally deposited gold, X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) indicate that the first monolayer (ML) grows two dimensionally, while additional gold forms islands, and that the surface becomes metallic by 1 ML. Downward band bending for low coverage is confirmed by a comparison of the XPS valence and UPS spectra, which have different detection depths. Inverse photoelectron spectroscopy (IPES) shows that the deposited gold attenuates the Ti 3d states, which dominate the conduction band. In the case of lithium, XPS analysis indicates that deposited atoms penetrate into the bulk, with a gradual buildup in the near-surface region. UPS shows the formation of a Ti3+ 3d gap state 1.4 eV below the Fermi level. Band bending is not observed for low Li coverage due to pinning of the Fermi level to the gap state. Deposition of more than 10 ML is required for the work function to reach that of bulk Li. Unoccupied 3d states disappear from the IPES spectrum as they are filled by electrons injected from Li.

Electronic state changes of Cu nanoparticles on rutile TiO2(110) by O2 and CO exposure

In order to investigate the strong catalytic activities of Cu nanoparticles, we have measured the electronic states of oxygen and carbon monoxide-exposed Cu nanoparticles on the rutile TiO2(110) surfaces by synchrotron radiation photoelectron spectroscopy. After depositing Cu on the oxygen rich TiO2(110) (O-TiO2) surface, the Ti 3d state appeared due to the disappearance of the oxygen adatoms by reaction with Cu. After further oxygen exposure, Cu 3d state drastically changed. This result indicates that Cu2O is formed by oxidation of Cu nanoparticles. We then dosed a CO gas onto the oxidized Cu/O-TiO2(110) surface and found that the work function slightly decreases and elimination of O adatoms is confirmed by medium energy ion scattering. These results obtained clearly shows the reaction of CO with O adatoms adsorbed on Cu/TiO2 probably to form CO2.

Electronic and lattice properties of nanostructured TiN/MgO and ScN/MgO superlattices

Various nanostructured TMN(001) dot/MgO(001) (TM = Sc, Ti) superlattices have been investigated. Here, we consider single and double layered TM dot structures with rectangular and rectangular parallelepiped shapes. MgO-2 × 2 and −3 × 3 substrates were used. Their electronic states were obtained using a total energy pseudopotential method. The internal atomic coordinates from the repeated slab model in the unit cell were fully relaxed. Various relaxed structures and electronic properties of the TMN(001) dot/MgO-2 × 2 and −3 × 3 superlattices were obtained. We determined their total and partial densities of states. Peaks of density of states (DOS) of the ScN dot/MgO superlattices around the band gap consist of Sc 3d and N 2p states and those of the TiN dot/MgO superlattices consist of mainly Ti 3d states. The largest band gap value in the TiN(001) dot/MgO(001) (ScN(001) dot/MgO(001)) superlattice is 1.22 eV (1.48 eV) from the density-functional theory-local density approximation calculation. The electronic properties (band gap values, DOS curves, and many more) vary with varying dot shape and substrate size. Most band gap values corrected using a generalized density-functional theory were improved.