Cr Doping Research Articles

UV/blue/green converted efficient red-NIR photoluminescence in Cr incorporated MgAl2O4 nanocrystals: Site selective emission tailored through cation inversion and intrinsic defects

The UV/visible activated near-infrared (NIR) phosphors have many applications in solid state lighting, night vision devices and bio-imaging. The early research reported the red-NIR emitting phosphors doped with Cr3+ centers upon visible light excitation. Here, in this work the intense red-NIR emission and color tuning is achieved for broad excitation range (UV/blue/green) through Cr dopant induced defect centers and cation inversion in MgCr Al2O4 ( = 0.5, 1, 3, 5 and 10 mol%) nanocrystals. The Cr3+ doped MgAl2O4 nanocrystals were synthesized by combustion method through stoichiometric substitution of Mg by Cr, while most of the Cr3+ ions occupied the octahedral sites of spinel host with the formation of antisite defects, Cr3+ clusters, magnesium and oxygen vacancies. These defect centers were probed through Rietveld refinement, photoluminescence (PL), x-ray photoelectron and nuclear magnetic resonance spectra analyses. At UV excitation, the intrinsic defects played an interesting role in exhibiting the blue-violet emission attributed to host lattice defects and red-NIR emission attributed to strong/weak ligand field octahedral Cr3+ sites, via charge transfer to Cr3+ ions. The PL spectra evinced the enhanced red-NIR emission intensity upon 266 nm excitation than upon blue and green light excitation. Further, the weak ligand field site emission is found to be dominating with increase in doping concentration. Thus, Cr doped MgAl2O4 nanocrystals showed their potency of exhibiting the intense red-NIR emission and color tuning (from red purple to bluish purple and then to red color) upon UV/blue/green excitation.

Fe-doped SnSe monolayer: A promising 2D material for reusable SO2 gas sensor with high sensitivity

Recently, 2D materials have attracted great interest in the gas-sensing field, in which TMMC GeS, GeSe, SnS, and SnSe monolayers have been reported as promising SO2 sensing materials [Chem. Phys. Lett. 686 (2017) 83–87; Appl. Surf. Sci. 484 (2019) 33–38]. However, the transport properties, sensitivity, and recovery times of such structures related to the adsorption of SO2 molecule have not been published to date. In this work, we found that the recovery times of the pristine GeS, GeSe, SnS, and SnSe monolayers after SO2 adsorption are too short, indicating their low application possibility for SO2 sensing materials. Interestingly, the transition metals doping (Cr, Mn, or Fe) improves the recovery time of the SnSe monolayer in respect of SO2 molecules. Especially the calculated recovery time of the Fe-doped SnSe monolayer in respect of SO2 molecules at 373 K is 27 s, which is suitable for reusable gas sensors. Moreover, we first designed an SO2 gas sensor based on the Fe-doped SnSe monolayer with two Au electrodes. The NEGF formalism-based calculations show its high sensitivity to an SO2 molecule. Our results suggest that the Fe-doped SnSe monolayer is a promising 2D material for reusable SO2 gas sensors with high sensitivity.

Dopant-based modulation of structural, electronic, and electrochemical properties of Li-excessive Li2NiO2 cathodes

Despite the importance of establishing a suitable doping strategy for high-potential Li2NiO2-based cathode materials, relevant studies are lacking to be explored. This study systematically explores the structural, electronic, and electrochemical properties for a series of transition metal-doped, Li-excessive, layered Li2NiO2 materials. The incorporation of Cr dopant with electronically suitable d orbitals is revealed to be the best choice to design high-voltage Li2NiO2 cathode materials with little sacrifice of energy density and structural stability. Further investigation highlights that the d-orbital based design of a proper dopant would be a key strategy to develop Li2NiO2-based cathode materials with high-performance battery applications.

Influence of Cr Doping on Structural, Optical, and Photovoltaic Properties of BiFeO3 Synthesized by Sol-Gel Method

In this work, pure BiFeO3 and samples doped with different concentrations of chromium were synthesized to improve the optical properties and efficiency of solar cells based on BiFeO3. The sol-gel method was used for synthesis due to its ability to produce nanostructured materials with high purity and good homogeneity, as well as the possibility of controlling the size and shape of the resulting particles. The samples were characterized by different analytical techniques. Thermal analysis results indicate that the dopant increases the weight loss of the sample from 61 to 81%, with an increase in the exothermal in the nucleation and crystallization temperature range. The X-ray diffraction patterns and UV-visible spectra show a dependence of the crystallite size and bandgap with respect to the amount of Cr dopant, decreasing from 168 to 73 nm and from 2.14 to 1.92 eV, respectively. Scanning electron microscopy images display a decreasing grain size as a result of an increasing amount of dopant. The I-V analysis results show a 1% Cr-doped BiFeO3 photovoltaic device exhibits enhanced photovoltaic performance with higher photocurrent and 4.17 times greater energy conversion efficiency compared with a pure BiFeO3 photovoltaic device. For their behavior, Cr-doped BiFeO3-based photoelectrodes are very promising materials for photovoltaic devices.

Effect of Cr and La co-doping on the photocatalytic hydrogen production performance of Sr1-xLaxTi1-xCrxO3 nanofibers

The Sr1-xLaxTi1-xCrxO3 (x = 0–0.05) nanofibers were synthesized by electrospinning based on Pechini sol-gel method. The prepared Sr1-xLaxTi1-xCrxO3 nanofibers were analyzed by XRD, Raman, UV–vis spectra, XPS, SEM, TEM, transient photocurrent, electrochemical impedance and photocatalytic hydrogen evolution tests. The results showed that CrLa co-doped can expand the light absorption region of SrTiO3 from the ultraviolet region to the visible light, and significantly narrowed its band gap. Under visible light irradiation, Sr1-xLaxTi1-xCrxO3 nanofibers exhibited the best hydrogen evolution activity at x = 0.03, and the hydrogen evolution rate reached 106.2 μmol∙g−1∙h−1. This may be the result of the combined effect of the intermediate band gap and the band gap variation due to Cr doping.

Investigation of the crystal structure, electronic and optical properties of Cr-doped BaTiO3 on the Ti site using first principles calculations

In this work, we have investigated the effect of chromium (Cr) doping on the structural, electronic and optical properties of the cubic phase of BaTiO3 using first-principles calculations. Applying the GGA + U approximation, the lattice parameters as well as the band gaps of the undoped and doped phase of BaTiO3 are in fairly good agreement with the experimental data, confirming the validity of our model. Furthermore, the chemical bonding analysis underlines the ionic character of Ba–O bonds and the covalent nature of Ti–O and Cr–O bonds. Additionally, the investigation of the optical properties using the Hubbard U-potential correction provided good agreement with the experimental data in the broad energy ranges. We have also demonstrated that the substitution of chromium on the Ti site, through the calculation of both electronic and optical properties, leads to the appearance of defects close to the Fermi level, allowing the appearance of the asymmetry of the BaTi1-xCrxO3 system. As a result, the calculated total magnetic moment is 1.6038 μB, indicating that doping with Cr renders the BaTi1-xCrxO3 system ferromagnetic. Therefore, this work demonstrates that Cr-doped BaTiO3 could reasonably constitute a new class of perovskite materials for magneto-optoelectronic applications.

Oxidation and phase transfer of individual Cr-doped dendritic FeOx particles visualized by full-field nano-XAFS spectroimaging.

Iron oxides with various compositions and polymorphs have been widely used as compounds that require reversible redox properties, such as catalysts. However, partial decomposition during phase transitions often causes irreversible degradation of the redox properties of iron oxides. Cr doping into the crystalline framework of iron oxide dendrites improves the stability of the structural transformation of iron oxides. We spatially visualized the FeOx-dendrite phase distribution during oxidation in crystalline dendritic FeOx and Cr-FeOx particles by full-field nano-X-ray absorption fine structure spectroimaging. The spectroimaging visualized propagation in the phase transitions in the individual FeOx particles and changes in the phase transition behaviors of the Cr-FeOx particles. The statistical analysis of the spectroimaging data revealed the phase transition trends in parts of the FeOx and Cr-FeOx particles in three Fe density zones (particle thicknesses) and the probability densities of the phase proportions in the dendrites.

Exploration of electrodeposited process of Ni-Co-Cr coating and investigation of Cr doping strengthening mechanism by indentation simulation

Ni-Co-Cr coating with excellent mechanical properties was successfully prepared by the electrodeposition process. Compared with the binary Ni-Co alloy coating, the hardness of the ternary coating is increased to 1247HV, an increase of 61%. The wear rate decreased by 40.7%. The exploration of the deposition process found that sodium formate and urea can effectively dissociate [Cr(H 2 O) 6 ] +3 complexes to realize the co-deposition of Cr 3+ . The strengthening mechanism of Cr doping was then investigated by molecular dynamics indentation simulation. It is found that grain refinement and solid solution strengthening contribute 20% (0.33 GPa) and 80% (1.33 GPa) to the hardness, respectively. The enhanced covalent character between Cr and solvent atoms improves the elastic modulus and promotes the dislocation nucleation, which originates from body-centered cubic-like (BCC-like) defect clusters. In the plastic deformation stage, Cr doping reduces the stacking fault energy of the alloy and makes the release of the plastic strain more uniform and stable. The denser 3D stacking fault network structures hinder the further propagation of dislocation loops and increase the dislocation reaction probability. More Lomer-Cottrell and Hirth Locks are generated and improve the strength of the coating. • An electrodeposited Ni-Co-Cr coating with excellent mechanical properties was developed. • The contribution of grain refinement and solid solution strengthening to hardness was quantitatively investigated. • The strengthening in the elastic stages comes from the enhanced covalent character between Cr and solvent atoms. • The strengthening in the plastic stages comes from the increase in the number of immobile dislocations.

Tuning the lattice thermal conductivity of Sb2Te3 by Cr doping: a deep potential molecular dynamics study.

Element doping is a prominent method for reducing the lattice thermal conductivity and optimizing the thermoelectric performance of materials in the thermoelectric field. However, determination of the thermal conductivity of element-doped systems is a challenging task, especially when the elements are randomly doped. In this work, a first-principles based deep neural network potential (NNP) is developed to investigate the lattice thermal transport properties of Cr-doped Sb2Te3 using molecular dynamics simulations. Compared with pure Sb2Te3, the thermal conductivity of orderly Cr-doped Sb2Te3 with Cr atoms locating at specific atomic layer positions decreases slightly in the in-plane direction, but sharply in the out-of-plane direction. The decrease of the low frequency phonon density of states and the enhancement of phonon scattering near 2.5 THz are the primary reasons for the decrease in the thermal conductivity of Cr-doped Sb2Te3, while the decrease of phonon velocity due to band flattening is the reason for the sharp decrease of thermal conductivity in the out-of-plane direction. Moreover, the thermal conductivities of randomly Cr-doped Sb2Te3 with different Cr concentrations are also investigated using the NNP. It is found that the thermal conductivities in both the in-plane and out-of-plane directions are reduced by 76% and 80%, respectively, for Sb36Cr36Te108. Furthermore, the influence of different Cr dopant arrays on the thermal conductivity of Sb2Te3 is also predicted using the NNP. Our work provides a good example for predicting the thermal conductivity of element-doped systems using the NNP combined with molecular dynamics simulations.

Effects of Chromium (Cr) doping on Structural, Electronic and Magnetic Properties of Barium Selenide Compound: A Theoretical Investigation

Effects of Chromium (Cr) doping on Structural, Electronic and Magnetic Properties of Barium Selenide Compound: A Theoretical Investigation

Growth of a hexagonal α-Fe1−xCrxSe (x ≥ 0.4) alloying phase with room-temperature high coercivity by Cr introduction

3d transition metal chalcogenides have gradually become candidates for magnetic materials due to their unique d-electronic structures. However, a relatively lower Curie temperature (TC) and coercivity (HC) limit their widespread applications. Here, we report a high-temperature organic-solvent-phase method for the synthesis of hexagonal α-Fe1−xCrxSe (0 ≤x ≤ 0.6) alloyed nanosheets with high TC through Cr introduction. Without Cr introduction, FeSe nanosheets appear as a mixture of tetragonal β-FeSe and hexagonal α-FeSe phases with a soft/hard decoupled hysteresis loop of HC∼3.35 kOe at 5 K. With an increase in the Cr content, α-Fe1−xCrxSe gradually becomes dominant. The tetragonal-to-hexagonal phase transition is completed at the optimum doping of Cr (x = 0.4), and α-Fe1−xCrxSe exhibits hard magnetic behavior. The coercivity (HC) can be as high as 15.80 kOe at 5 K and 4.98 kOe at 300 K when the Cr concentration reaches 60%. The synthesis of α-Fe1−xCrxSe alloy provides a potential material for hard magnets. Therefore, the doping-induced phase transition is an effective way to synthesize ideal phase nanomaterials.

A first principles study on H-atom interaction with bcc metals

Solute hydrogen trapping has long been proposed as one of the mechanisms for hydrogen embrittlement in steel. It has been reported that the maximum hydrogen trapping energy of metallic solutes ranged from −0.7 eV to −0.9 eV. In this work, the mechanism of metal-H interaction in Cr-Mo steels was investigated with first principles calculations by modelling the binary alloy Fe-X (X = C, Si, Mn, Cr, Mo) system with reference to the chemical composition of Cr-Mo steels. The formation of hydrogen bonds in the case of H atoms located at different sites in Fe-X crystals was analyzed. Results indicated that various atomic doping had different roles in hydrogen effect in the steel, with C, Si and Mo doping making the solid solution of hydrogen in Fe crystals easier, while Mn and Cr doping was rather more difficult. In Fe-Mn and Fe-Cr crystals, the repulsion between Fe lattices was insignificant when H atoms were located in tetrahedral sites, which considerably reduced the binding energy in the crystal. When H atoms were dissolved into the crystal, the interatomic bonding interactions in Fe-X crystals were weakened, resulting in higher charge density fluctuations. The current work extends the understanding of H-atom diffusion and migration in steel from the microscopic scale to the atomic and electronic scales, which underpins the physics for tailoring chemical elements of bcc metals towards higher resistance to hydrogen embrittlement.

Improving Performance of an Integrated Solar Flow Battery by Cr- and Cu-Doped TiO2 Photoelectrodes.

This work reports on the preparation of Cr-doped TiO2 (Cr−TiO2), Cu-doped (Cu-TiO2), and its utilization in the photoanode of a solar redox flow battery (SRFB). A pure TiO2 electrode, Cr-doped TiO2 electrode, and Cu-doped TiO2 electrode coated with different layers are prepared by the sol-gel method. XRD, XPS, and SEM are used to characterize the relevant data of the electrode. All three electrodes show the structure of the anatase phase, but the Cu-TiO2 and Cr-TiO2 electrodes are more crystalline. Using these materials as photoelectrodes to prepare integrated solar flow cells, the semi-cell and full-cell tests show that the doping of Cr and Cu improves the efficiency and charging current of solar cells. The average charging currents of the Cu-TiO2 and Cr-TiO2 electrodes are 384.20 μA and 450.75 μA, respectively, compared with the TiO2 electrode; this increment reaches values of 71.23% and 100.97%.

Enhanced and rapid photocatalytic degradation of toxic dyes by cobalt oxide and modified cobalt oxide under solar light irradiation

A solar light driven photo degradation approach for methylene blue (MB, model molecule of the thiazine dyes class) and malachite green (MG, model molecule of the triphenylmethane category) abatement by Co3O4 and Cr-Co3O4 spinel nanoparticles is reported. The effect of chromium load (5, 10 and 15%) in Co3O4 particles, synthesized by a simple co-precipitation process, was properly studied. The structural and morphological characteristics, chemical composition and optical properties of the materials were investigated by X-ray diffraction (XRD), Transmission Electron Microscopy(TEM), Field Emission Scanning Electron Microscopy – Energy Dispersive Spectroscopy (FE-SEM-EDS), FT-IR spectroscopy, UV–Vis diffuse reflectance spectroscopy (DRS),photoluminescence (PL) and BET surface area analysis. It was observed that properly tuning the initial pH, the initial dye concentration, the agitation time, and the photocatalyst dose, (10)Cr-Co3O4 exhibited an enhanced photocatalytic activity compared to that of pristine Co3O4, demonstrating the positive role of Cr doping In fact, the PL investigation showed that Cr doping in the Co3O4 lattice greatly increase the separation of electron-hole (e−/h+) pairs, whereas the UV DRS spectra and Tauc plot revealed a decrease in the band gap energy for Cr-Co3O4,. The investigations demonstrated that the MB dye degradation increases from 88% to 96% at pH = 11 after doping of Co3Oby 10% of Cr. Similarly, the Cr doping allowed to enhance the MG dye degradation from 85% to 92% at pH = 9. The photo degradation kinetics of both MB and MG dyes by Cr-Co3O4 and Co3O4 NPs were of pseudo-first-order mode. The active species involved in the photocatalytic process were properly identified using various scavengers by trapping holes and radicals. Finally, the photocatalysts showed good stability during recycling maintaining high performances after 5-time usage. .

Modulating spintronic properties of transition metals doped GaN nanotubes with high Curie temperature

AbstractBetween the ferromagnetic semiconductors of the III‐V group, the transition metals (TMs) doped gallium nitride (Ga, TM)N diluted magnetic semiconductor (DMS) shows the most well‐understood and promising applications in spintronic, due to its high Curie temperature. In this research, electronic and magnetic properties of pure armchair (3, 3) and zigzag (5, 0) gallium nitride nanotubes (GaNNTs) and doped with TMs are investigated using the spin‐polarized density functional theory. The spin‐polarized DOS revealed that pure zigzag and armchair GaNNTs are nonmagnetic semiconductors with a direct and indirect bandgap, respectively, in contrast, TMs doped GaNNTs are DMS or half metals (HM). Our results show a high Curie temperature of more than 823 K for Cr and Mn doping, indicating may be good room‐temperature ferromagnetic material for spintronic applications in the future. 11% Cr and Mn atoms doped (3, 3) GaNNT are HM with 100% spin polarization and appear to be good candidates for spintronic applications and especially as spin filter devices.

Facile Synthesis of Pure and Cr-Doped WO3 Thin Films for the Detection of Xylene at Room Temperature.

This paper focused on the preparation of pure and Cr-doped tungsten trioxide (WO3) thin films using the spray pyrolysis method. Different techniques were adopted to analyze these films' structural and morphological properties. The X-ray detection analysis showed that the average crystallite size of the WO3-nanostructured thin films increased as the Cr doping concentration increased. The atomic force microscopy results showed that the root-mean-square roughness of the films increased with Cr doping concentration up to 3 wt % and then decreased. The increased roughness is favorable for gas-sensing applications. Surface morphology and elemental analysis of the films were studied by field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy measurements. The 3 wt % Cr-WO3 has a large nanoflake-like structure with high surface roughness and porous morphology. Gas-sensing characteristics of undoped and Cr-doped WO3 thin films were investigated with various gases at room temperature. The results showed that 3 wt % Cr-doped WO3 film performed the maximum response toward 50 ppm of xylene with excellent selectivity at room temperature. We believe that increased lattice defects, surface morphology, and roughness due to Cr doping in the WO3 crystal matrix might be responsible for increased xylene sensitivity.

Discovery of a novel visible-light-active photodetector based on bismuth ferrite: constructing and optimizing the Cr-doped-BiFeO3/NiO thin film heterostructure

Bismuth ferrite (BFO) with narrow bandgap (<2.70 eV) is an uprising star in the application of optoelectronic conversion in visible (Vis) region. Fe-site doping by transition metals is a recognized strategy to reduce leakage current in order to create more qualified BFO-based optoelectronic devices. We aim to constitute the heterostructure of BiFe1-xCrxO3 (BFCO) coupling to hole-transporter NiO, serving as Vis-active photodetector with superior photoresponse speed. The influence of Cr doping ratio on BFCO is systematically investigated, indicating that doping Cr can effectively restrain not only the reduction of Fe3+ state but also the generation of oxygen vacancies. Moreover, by taking advantage of desirable energy-band alignment, BFCO/NiO heterojunction can reach the optimized response time constants of photocurrent rising and decay, i.e., τr and τd are, respectively, lowered down to 0.23 and 0.38 ms, which are almost two order-of-magnitude lower than that of pure-BFO/NiO and also more than one order-of-magnitude lower than that of single-layer BFCO film. It confirms an overwhelming photoresponse performance over other Vis-active counterparts. Herein, we for the first time achieve the Vis photodetector based on BFCO, by virtue of functional interfacial structure of BFCO-NiO to energetically separate photogenerated electron–hole pairs as well as improve charge carrier transportation.

Microstructures, Composition and Tribological Behavior of TiCrN/MoS2–TiCr Coatings Deposited by Magnetron Sputtering

To enhance the tribological performance of the conventional TiCrN coating, the MoS2–TiCr coatings are deposited onto the TiCrN layer by magnetron sputtering. In general, the MoS2 is implemented to enhance the friction reduction performance of the TiCrN coating, while the Ti and Cr are doped to increase the density of the structure and prevent MoS2 from oxidizing. The results reveal that with an increase in the content of Ti and Cr in the MoS2–TiCr top layer, the hardness and the coating–substrate adhesion force of the composite coating increase, respectively, due to the compact top layer. Further, the optimized Ti and Cr doping in the MoS2 top layer greatly enhances the tribological properties of the TiCrN/MoS2–TiCr composite coating with a friction coefficient as low as 0.06 and the wear rate is only 6% of the TiCrN coating. The main reason for the excellent tribological properties of the TiCrN/MoS2–TiCr composite coating is probably due to the recrystallization of the MoS2 in the process of wear.

Electronic property and effective diffusion coefficient calculation model of hydrogen isotopes in multicomponent steel 2.25Cr1Mo from first-principles calculations

Chrome-molybdenum (2.25Cr1Mo) ferritic steel is one of the primary materials used in heat exchanger pipes in the steam generators of high-temperature gas-cooled reactors (HTGRs). Studying the tritium diffusion mechanism in 2.25Cr1Mo ferritic steel is of vital importance for the prediction and interpretation of tritium activity concentration in the reactor. However, the permeation of hydrogen isotopes in these alloys remains difficult to predict owing to the lack of understanding of the microscopic interactions between hydrogen isotopes and multicomponent alloys. In this study, the electronic and diffusion properties of the hydrogen isotopes in 2.25Cr1Mo alloy were investigated using first-principles calculations. Hydrogen preferentially intercalated into tetrahedral interstitial sites rather than octahedral ones in 2.25Cr1Mo alloy. The Cr and Mo dopants induced strong repulsion between H and the matrix. Interaction between H and 2.25Cr1Mo exhibited a combination of ionic and covalent bonds with electrons transferred from the steel to H atom. Dopants acted as scattering centers with local interaction with H and expanded the preventive effect of H diffusion to the second-nearest tetrahedral interstitials with a high energy barrier. The effective H diffusion coefficient in the alloy was calculated by an approximate model based on the volumetric ratio of the components for the first time. The obtained pre-exponential factor and activation energy agreed well with the experimental results. The current research provides a reliable way to determine the effective diffusion coefficient of hydrogen isotopes in multielement alloys, which can accelerate R&D of tritium-resistant materials in both fusion and fission reactors.

Superelasticity by introductions of Cr into the Ti-Zr-Nb-Sn strain glass alloy toward the elastocaloric application

In this study, new superelastic Ti-18Zr-9 Nb-2Sn-(1−2)Cr (at%) alloys were fabricated by an arc melting method and annealed at different temperatures for 0.6 ks to obtain β-titanium elastocaloric materials. Their phase constituents, strain glass transition behavior, superelasticity, and textural characteristics were analyzed by X-ray diffraction, dynamic mechanical response, tensile tests, and electron back-scattered diffraction, respectively. The strain glass transition behavior exhibited a dependence on the Cr doping content and annealing temperature: 1 at% Cr reduced the transition temperature T0 of the sample by about 50 K, while T0 decreased gradually from 242 K to 218 K with the annealing temperature. A highly dominant {111}β< 110 >β texture and high-density fine subgrains were obtained in the Ti-18Zr-9 Nb-2Sn-1.5Cr alloy annealed at 923 K. The sample had a superelastic strain of 3.80 % and critical stress of 520 MPa. Finally, a stable and reproducible adiabatic temperature change of 4.20 K was obtained at room temperature.