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TG curves and ionic current lines (m/z = 18 and m/z = 44) for decomposition of SrTiO3 and SrTi1−xNbxO3 before (a) and after (b) exposition tests
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A series of porous SrTi1−xNbxO3 samples (with x = 0, 1, 2 and 3 mol%) were prepared by wet synthesis and sintered at 1573 K. Single phase samples were obtained for each composition, as confirmed by XRD measurements. For all samples, aging tests in CO2/H2O atmosphere and electrochemical impedance spectroscopy measurements in air and hydrogen (reduce...
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Citations
... Co-3d states show splitting into doubly degenerate eg and triple degenerate t2g groups (the later one mostly contributing in VB in spin up channel and in lower part of the CB in spin down channel, while the former splitting state is highly polarized in higher VB, almost overlapping the EF). Similar like d-splitting into eg and t2g groups in Nb-doped STO system was reported by Drożdż et al., back in 2017 [42]. ...
Ferromagnetic semiconductors or half metals offer strategic advantage in spintronic applications due to their robust stray fields and ultrafast magnetic dynamics. Controlling their magnetization and readout of their magnetic state are essential for these applications but remain challenging. Herein, we present a density functional theory (DFT) based full potential linearized augmented plane wave (FP-LAPW) analysis of the magneto-optical properties of novel and most widely studied diamagnetic SrTiO3 (STO) doped with cobalt. Pure STO is non-magnetic wide band gap (3.25 eV) semiconductor. Our study shows that versatile transport and magnetic properties can be obtained in CoxSr1-xTiO3, ranging from magnetic semiconductor to half metallic ferromagnetic nature depending upon the dopant's concentration. Spin resolved electronic properties and non-zero values of calculated magnetic moments for doped supercells reveal that Co0·125Sr0·875TiO3 and Co0·25Sr0·75TiO3 are good DMSs while Co0·5Sr0·5TiO3 and Co0·75Sr0·25TiO3 are half metallic ferromagnets. The analysis of band structures and density of states reveal that partially filled Co-3d and O-2p states show hybridization. Moreover, calculated optical conductivity lie in the visible region of the order of 103 (Ω cm)−1 while reflectivity in this region is minimum. Our findings demonstrate Co doping as a powerful approach to control the magneto-optoelectronic physics in STO, which will stimulate further experimental research with promise for tailored magnetic and optoelectronic properties in Co doped STO systems.
... This widened the band gap of the 0.01 wt% Nb-doped STO semiconductor, enhancing its usefulness for various energy conversion and environmental purposes [21]. SrTi 1-x Nb x O 3 where x = 0, 1, 2, 3 mol%, synthesized via wet synthesis, resulted in a shift of the Fermi level [22]. Additionally, 0.1% of Nb-doped TiO 2 , was found to be the optimum level for suppressing the surface recombination [23]. ...
... Additionally, it was observed that the crystallite size of the STNO powders prepared in this way is relatively smaller than the crystallite size of the STO nanopowder synthesized by a modified aerogel procedure (25 nm) [36], the Sr 0.94 Ti 0.9 Nb 0.1 O 3 (80 nm) synthesized by a modified glycine-nitrate process (80 nm) [37], or the STNO (x = 0-0.03) nanopowders prepared by the wet synthesissol-gel method (160-240 nm) [22]. Considering the effect of Nb doping on the STNO cubic perovskite structure, the specific structural parameters were calculated by Rietveld refinement analysis of the experimented XRD data using the Fullprof program. ...
Metal oxide photocatalyst is a promising wastewater treatment process due to its simplicity, high efficiency, and low cost, as well as being environmentally friendly and non-energy consuming. The perovskite structure material, SrTi1−xNbxO3 (STNO) with x = 0, 0.01, 0.03, and 0.05, was successfully synthesized by the sol-gel auto-combustion method. Samples with a pure phase and cubic perovskite structure were obtained. The Rietveld refinement results showed that the lattice parameter and unit cell density increased as the Nb-doping level increased. The particle size of the STNO decreases with increasing Nb doping content. Photoluminescence was excited at 327 nm, producing violet, green, and blue emissions, while the Nb content asserts an insignificant effect on the bandgap (Eg). The Nyquist plot and Mott-Schottky analysis were used to determine the photoelectrode performance of the STNO samples. The photocatalytic activity of STNO on the decolorization of methylene blue (MB) under UV irradiation increased with increasing Nb content and optimization at x = 0.05, corresponding to the results obtained from photoluminescence, Eg, Nyquist plot, and Mott-Schottky analyses.
... We observe that the pentavalent substitution, like the Nb, moves the Fermi level into the conduction band, making the material metallic and lying approximately 0.44 eV from its bottom-most point. The lattice constant optimizes to a value close to 3.937 Å, and the band structure reveals a behavior similar to the experimental results where the STO turns into an n-type semiconductor [45]. In SrTiO 3 , the band structure calculations show that the conduction band's minimum is at the Γ point, and the bands are threefold degenerate at this k-point. ...
In SrTiO 3 , the nature of dopants and their substitution at the A or B site becomes a critical factor in determining the electrical conductivity, Seebeck coefficient, and thermal conductivity. The electronic band structure and the density of states (DOS) for the ab-initio study using different dopants were estimated using PBE-GGA approximation. The size, site of substitution, and nature of dopants cause significant changes in the lattice dimensions, band structure, band curvatures, and the density of states, which reflect as changes in the effective mass m B i ⁎ . The effective mass m B i ⁎ is calculated from the curvature of the bottom-most conduction band using the one-band effective mass approximation. Pentavalent substitutions on the B site of SrTiO 3 affect the conduction band’s curvature differently than with trivalent substitutions on the A site. They also exhibit an opposite trend in the change in band curvature according to the dopant’s ionic radius. In contrast, isovalent dopants showed no change in the band curvature except for the bandgap modification. In this paper, we have provided a semi-quantitative understanding regarding the thermoelectric properties like conductivity and Seebeck coefficient that get affected due to the substituent’s nature and site at which it substitutes.
... Exploiting the potential of doped perovskites, due to their chemical stability and good electrochemical properties, is another direction in the search for alternative materials for SOFC anodes. In the literature, there are a few articles devoted to the study of such materials in terms of their use as anodes in SOFCs powered by biogas [10,11], although doped SrTiO 3 materials have already been tested for application as an anodic material for hydrogen-fuelled SOFCs, including ytterbium [12], niobium [13,14], yttrium [15] and lanthanum-doped [16] strontium titanates. ...
Two series of strontium titanates doped with Ni, Co, or Cu with general formula of SrTi1-xMexO3 for Sr-stoichiometric and Sr0.95Ti1−xMexO3 for Sr-non-stoichiometric materials (where Me = Ni, Co or Cu and x were 0.02 and 0.06) were obtained by the wet chemical method. The samples were calcinated at 900, 950, and 1050 °C and characterized in terms of their structural properties (XRD), the possibility of undergoing the reduction and oxidation reactions (TPR/TPOx), and catalytic properties. All obtained materials were multiphase and although the XRD analysis does not confirm the presence of Ni, Co, and Cu oxides (with one exception for Cu-doped sample), the TPR/TPOx profiles show reduction peaks that can be attributed to the reduction of these oxides which may at first appear in an amorphous form. Catalytic tests in dry reforming of methane reaction showed that the highest catalytic activity was achieved for Ni-doped materials (up to 90% of CH4 conversion) while Co and Cu-doped samples showed only a very slight catalytic effect. Additionally, the decrease in methane conversion with an increasing calcination temperature was observed for Ni-doped strontium titanates.
... This is understood on the basis of grain boundaries and the Hall effect data listed in Table 2. Non-uniform grain distribution is likely to cause the reduction in carrier mobility of STO-650 since the grain boundaries retard or slow down the displacement of the charge carriers and hence, an additional energy is required to overcome the barrier and results in less mobility and hence, the higher activation energy. These data are comparable with the results reported in literature [44]. The plots of Seebeck coefficient versus temperature (S-T) are reported in Fig. 6(a). ...
The effect of substrate temperature on the surface morphology, electronic structure, and thermoelectric properties of SrTiO3 (STO) films were investigated using the atomic force microscopy, X-ray diffraction, X-ray absorption spectroscopy (XAS). The STO films were grown by pulsed laser deposition by varying the substrate temperatures from room temperature to 850 °C. A strong dependence of the lattice parameters and the surface morphology lead to the 3D island growth process with substrate temperature. The variation in the substrate temperature results in the evolution of the microstructure and the enhancement of electrical and thermoelectric properties. The large power factor of 10 μ Wm⁻¹ K⁻² at (400 K) is evident for the thin films deposited at the substrate temperature of 650 °C and is highly suitable for thermoelectric applications. The XAS spectra reveal the reduction in valence state and off-center displacement of Ti ions in TiO6 octahedron with substrate temperatures. These spectra shift to the lower energy side indicating the presence of oxygen vacancies that are responsible for the observed transport behaviour. These results show that the substrate temperature plays a significant role in tuning the electrical and thermoelectric properties due to O vacancies. Thus, the optimum growth temperature required for the deposition of the SrTiO3 films is 650 °C for thermoelectric applications.
... The electron mobility of STO (5-8 cm 2 V −1 S −1 ) is far more than that of TiO 2 (0.1-4 cm 2 V −1 S −1 ) at room temperature, which can provide a faster carrier diffusion rate and help to improve the device performance [24]. Furthermore, the high chemical durability of STO is also an advantage that cannot be ignored [25]. ...
We have demonstrated a photoelectrochemical solar-blind ultraviolet (UV) detector based on SrTiO 3 (STO) nanocrystalline film in this work. The assembled UV detector presents a high on/off ratio of about 6433 under periodic UV irradiation, a high photocurrent density of 220.6 μ A cm ⁻² , and a fast response time of 9 ms. By introducing a block layer (BL) on fluorine-doped tin oxide substrate, the response and decay times are shortened to 6 ms and 8 ms, respectively. The BL plays a crucial part in hindering the recombination of electrons from electrolyte carriers and avoiding short circuits. Due to its excellent light capture capability, the detector based on SrTiO 3 nanocrystalline exhibits high sensitivity to weak UV light (5 μ W cm ⁻² ). Moreover, the detector also exhibits visible-blind characteristics and a good linear response.
... The thermal activation energy (E a ) required for the transportation of charge carriers to the delocalized states can be derived by a simple Arrhenius law and it is given in Table 1. Figure 7(a) shows the Arrhenius plot of ln(ρ) vs. 1/T and E a is calculated from the slope. The thermal E a for pristine STO is derived to be 100 meV which is comparable to the reported experimental results 33 . It is found that the E a is found to decrease significantly after N ion implantation, i.e., in STO-N116 and STO-N516 as compared to the STO. ...
The SrTiO3 thin films were fabricated by pulsed laser deposition. Subsequently ion implantation with 60 keV N ions at two different fluences 1 × 10¹⁶ and 5 × 10¹⁶ ions/cm² and followed by annealing was carried out. Thin films were then characterized for electronic structure, morphology and transport properties. X-ray absorption spectroscopy reveals the local distortion of TiO6 octahedra and introduction of oxygen vacancies due to N implantation. The electrical and thermoelectric properties of these films were measured as a function of temperature to understand the conduction and scattering mechanisms. It is observed that the electrical conductivity and Seebeck coefficient (S) of these films are significantly enhanced for higher N ion fluence. The temperature dependent electrical resistivity has been analysed in the temperature range of 80–400 K, using various conduction mechanisms and fitted with band conduction, near neighbour hopping (NNH) and variable range hopping (VRH) models. It is revealed that the band conduction mechanism dominates at high temperature regime and in low temperature regime, there is a crossover between NNH and VRH. The S has been analysed using the relaxation time approximation model and dispersive transport mechanism in the temperature range of 300–400 K. Due to improvement in electrical conductivity and thermopower, the power factor is enhanced to 15 µWm⁻¹ K⁻² at 400 K at the higher ion fluence which is in the order of ten times higher as compared to the pristine films. This study suggests that ion beam can be used as an effective technique to selectively alter the electrical transport properties of oxide thermoelectric materials.
... This oxide is an n-type semiconductor with a bandgap energy of approximately 3.2 eV [10]. For this perovskite, the valence band (VB) is predominantly composed of O 2p orbitals, with a small contribution of Ti 3d orbitals, and the CB is composed mainly of 3d Ti orbitals and 3d Sr orbitals at high energies [11]. The photocatalytic activity of the Ti and Sr sites at the surface of the SrTiO 3 structure for reducing CO 2 was studied, and the results indicated that the chemical environment surrounding the Ti 4+ ions was propitious to the photoactivity and that SrTiO 3 promoted the electronic transitions [12]. ...
CaO/SrTiO 3 heterostructures were fabricated, and their photocatalytic activity for the discoloration of Rhodamine B (RhB)dye was evaluated. SrTiO 3 particles were obtained via a polymer precursor method, and heterojunctions in which CaO grew on SrTiO 3 crystalline particles were prepared via a sol-gel route. Characterization was performed using X-ray diffraction, transmission electron microscopy, and ultraviolet/visible/near-infrared, Raman, and photoluminescence spectroscopy. The photocatalytic activity of the heterostructures was verified by the discoloration of RhB using UV light. Defects caused by tensile strain in the interface region were verified when the calcium oxide grew on the strontium titanate, altering the defects of the material. In the heterojunctions, the defects of the monoionized and doubly ionized O (oxygen)vacancies had a greater contribution to the photocatalytic process than the defects at deep levels generated in the stress region and the direct transfer of charge between the conduction and valence bands.
... This approach is computationally very expensive with practical application limited to bigger concentrations and thus smaller supercells. The main advantage is, however, that this approach allows studying local properties (structure deformation, electron density, or bonding changes, etc., due to point defect-substitutional atom or vacancy), which is simply not possible in mean field approximations [133,134]. [125] and b dehydrated form [126] The procedure employed to construct supercell is very straightforward: One starts with original unit cell (in Fig. 1.4a the unit cell of SrTiO 3 cubic perovskite structure is shown) and extends the structure in one, two, or three dimensions, e.g., constructing 3 Â 3 Â 3 superstructure (Fig. 1.4b) one obtains new, three times bigger cubic superstructure ( Fig. 1.4c) with 27-fold increased number of atoms. In this way, it is possible to substitute from 1 to 13 host atoms at B-cation position and simulate the substitution with the ratios of 1:28, 2:27, …13:14, corresponding to the dopant concentration wrt B-cation of approximately 3 at.%, ...
Spectroscopy investigates the interaction of electromagnetic radiation with matter. Along with the development of theoretical methods, increasingly effective numerical algorithms and computational methods as well as computer technologies and resulting growing computer power available for scientists, the so-called in silico experiments—computer simulations of materials and their properties in computer—have become an irreplaceable tool supporting experimental research, often allowing a better understanding of phenomena taking place during these interactions, and associated material properties. As a result, it becomes possible in growing number of cases to effectively design new materials with desired properties and to modify existing ones, to improve their properties. This chapter is devoted to a brief introduction to issues related to theoretical foundations of quantum mechanics and density functional theory, both in stationary and time-dependent form. The key assumptions of these theories are presented, together with the description of various approximations and simplifications necessary for their practical application to the calculation of properties examined by spectroscopic methods. The most important practical problems encountered during calculations, resulting from the complexity of real materials and typical ways of dealing with these problems by means of various simplifications, idealizations, and abstractions in designed structural models corresponding to real materials, are also presented.
