Cr Doping Research Articles

Bandgap regulation and doping modification of Ga2-x Cr x Se3 nanosheets.

Ga2Se3, an important direct wide bandgap semiconductor with excellent optoelectronic properties, has wide application potential in the fields of photodetectors, photoelectric sensors and solar cells. Herein, we describe the synthesis of Ga2Se3 semiconductor nanoparticles using a high temperature organic liquid phase method. Post-annealing treatment at different temperatures can not only improve the crystallinity of Ga2Se3 nanoparticles, but also regulate its optical band gap ranging from 2.50 to 2.80 eV. We further synthesized Ga2-x Cr x Se3 nanosheets by doping CrCl3·6H2O in the reaction process. By adjusting the Cr doping concentration, Ga2-x Cr x Se3 nanosheets can achieve a continuously tunable band gap in the range of 2.23 eV to 2.42 eV. Both Ga2-x Cr x Se3 nanosheets and Ga2Se3 nanoparticles exhibit excellent and stable photoelectric switching performance. With Cr doping, Ga2-x Cr x Se3 exhibits reduced Nyquist impedance and enhanced electrocatalytic activity, which is attributed to its ultrathin nanosheet morphology and large specific surface area. In addition, the diamagnetic behavior of pure Ga2Se3 changes to ferromagnetism with different Cr doping concentrations, and its magnetization is as high as 18.0 emu g-1 at x = 0.4. These findings demonstrate that Ga2-x Cr x Se3 nanosheets have significant potential in future optoelectronic and magnetoelectric applications.

Understanding the modulation mechanism of B-site doping on the thermochemical properties of CaMnO3−δ: an experimental and computational study

Cr and Fe doping disrupts the electronegativity and bond energy balance of CaMnO3, creating different active sites and enhancing the reactivity. Bond energy calculations allow the prediction of reaction temperature and reaction enthalpy.

First principles and molecular dynamics simulations of effect of dopants on properties of high strength steel for hydrogen storage vessels

High-pressure gaseous hydrogen storage is an important way of hydrogen energy storage and transport at present, while high-strength steel material is one of the main materials used for hydrogen storage vessels. However, their internal doping elements and inherent defects often lead their mechanical properties to decrease, thus reducing the pressure-bearing capability and storage life of the vessel. At present, the mechanism of doping elements influencing the mechanical properties of high-strength steels is still unclear. In this work, a first-principles approach is used to study the influence of elemental doping (Cr, Mn, Mo, As, Sb, Bi, Sn, Pb) on the mechanical properties of Fe single crystals and Fe-C systems. The results show that among the above elements, Mn doping can increase the elastic modulus, bulk modulus, and shear modulus compared with those of pure Fe, while the doping by remaining elements will reduce the three moduli above, with the non-transition metal elements having a greater effect on the three moduli than the transition metal elements. Electronic structure analysis shows that the transition metal elements have better compatibility with the Fe lattice. Molecular dynamics results further show that the injection of H atoms significantly disrupts the lattice ordering of the Fe polycrystalline doped by C, Cr, and Mn elements, while the doping of Cr elements can significantly enhance the dislocation density of the system. The effects of doping elements on the mechanical properties of single-crystal and polycrystalline Fe, which are studied in this work, are of great significance in guiding the mechanistic study of the effects of doping and defects on the strength of Fe-based materials.

Interface and Structural Engineering of Cr Doped Zinc Oxide/Graphene Photoanode with Enhanced Photoelectrochemical Water Splitting

The low-cost hydrogen (H2) generation from solar energy is one of the attractive and promising methods for clean and sustainable energy. It is challenging to boost global, renewable H2 energy mission. Until now, no catalytic system has been realized with viable efficiency and stability with reasonable manufacturing cost. Herein, we demonstrate a facile synthesis of chromium doped zinc oxide/graphene (Cr-doped ZnO@Graphene) as multicomponent photoanode using simple, inexpensive hydrothermal method. We investigated that graphene layer beneath ZnO can act in a different way, while salient features of controllable graphene concentration and appropriate Cr doping clearly displayed profound influence on photoelectrochemical water splitting reaction which is due to promoted electron transfer at interface. The detailed computational study was done by density functional theory (DFT) calculations. A photoelectrochemical cell was assembled with optimized photoanode displayed 4-fold increase in photocurrent density as compared to pristine ZnO. The improved PEC performance is attributed to the synergistic effects, where the presence of Cr dopant improves the charge carrier density and enhanced electronic conductivity, and graphene has increased the carrier transport and collection efficiency. Overall, this study provides valuable insights into the development of (Cr-doped ZnO@Graphene) as a highly efficient and stable photoelectrode for practical applications in solar water splitting and renewable energy conversion.

Tailoring Binding Abilities By Incorporating Oxophilic Transition Metals on 3D Nanostructured Ni Arrays for Accelerated Alkaline Hydrogen Evolution Reaction

Developing efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER) in alkaline water electrolysis plays a key role for renewable hydrogen energy technology. The slow reaction kinetics of HER in alkaline solutions, however, has hampered advances in high-performance hydrogen production. Herein, we investigated the trends in HER activity with respect to the binding energies of Ni-based thin film catalysts by incorporating a series of oxophilic transition metal atoms. It was found that the doping of oxophilic atoms enables the modulation of binding abilities of hydrogen and hydroxyl ions on the Ni surfaces, leading to the first establishment of a volcano relation between OH-binding energies and alkaline HER activities. In particular, Cr-incorporated Ni catalyst shows optimized OH-binding as well as H-binding energies for facilitating water dissociation and improving HER activity in alkaline media. Further enhancement of catalytic performance was achieved by introducing an array of three-dimensional (3D) Ni nanohelixes (NHs) that provide abundant surface active sites and effective channels for charge transfer and mass transport. The Cr dopants incorporated into the Ni NHs accelerate the dissociative adsorption process of water, resulting in remarkably enhanced catalytic activities in alkaline medium. Our approach can provide a rational design strategy and experimental methodology toward efficient bimetallic electrocatalysts for alkaline HER using earth-abundant elements.Reference Journal of the American Chemical Society 3, 1399-1408 (2021) [Front Cover]

Experimental and DFT studies on corrosion behaviors of laser-cladded (FeCoNi)75−xCrxB15Si10 high-entropy alloy coatings

The effects of Cr doping on microstructure evolutions and corrosion behaviors of laser-cladded (FeCoNi)75−xCrxB15Si10 (denoted as Crx hereafter, x = 0, 4, 8, 12, 16 at%) high-entropy alloy coatings (HEACs) were investigated. The composition and shape of the borides in interdendrite regions are modified by adding Cr, alleviating the localized corrosion behavior. The corrosion resistance of the HEACs increases continuously as a function of Cr level in 3.5 wt% NaCl solution. The Cr16 coating outperforms the previously reported Ni alloys, stainless steel, and some other high entropy alloys in terms of corrosion resistance, with the highest pitting potential (0.233 V), the lowest corrosion current density value of 9.9 × 10−9 A/cm2 and passive current density (2.138 ×10−8 A/cm2). Based on the experimental analysis and density functional theory (DFT) simulations, the corrosion mechanisms of the Crx HEACs were discussed. The exceptional corrosion resistance of the Cr16 coating can be attributed to its high oxygen adsorption energy and thus facilitates the rapid formation of protective and compact passive films with few defects.

Emergent zero-field anomalous Hall effect in a reconstructed rutile antiferromagnetic metal

The anomalous Hall effect (AHE) that emerges in antiferromagnetic metals shows intriguing physics and offers numerous potential applications. Magnets with a rutile crystal structure have recently received attention as a possible platform for a collinear-antiferromagnetism-induced AHE. RuO2 is a prototypical candidate material, however the AHE is prohibited at zero field by symmetry because of the high-symmetry [001] direction of the Néel vector at the ground state. Here, we show AHE at zero field in Cr-doped rutile, Ru0.8Cr0.2O2. The magnetization, transport and density functional theory calculations indicate that appropriate doping of Cr at Ru sites reconstructs the collinear antiferromagnetism in RuO2, resulting in a rotation of the Néel vector from [001] to [110] while maintaining a collinear antiferromagnetic state. The AHE with vanishing net moment in the Ru0.8Cr0.2O2 exhibits an orientation dependence consistent with the [110]-oriented Hall vector. These results demonstrate that material engineering by doping is a useful approach to manipulate AHE in antiferromagnetic metals.

Achieving Nearly Quantitative (∼100%) IQE and 42.3% EQE Across NIR‐I and NIR‐II Regions with Cr3+‐doped Cs2NaScCl6 under 300 nm Excitation

AbstractLead‐free rare‐earth‐based perovskites have received widespread attention for their unique optical properties, although achieving efficient broadband near‐infrared (NIR) emission with these materials remains a challenge. Here the synthesis of a rare earth‐based double perovskite (Cs2NaScCl6) by an improved solid phase method is reported. The doping of Cr3+ led to the formation of [CrCl6]3− octahedron, which exhibited a broadband NIR emission peaked at 950 nm and a half‐peak width of 162 nm. It is worth noting that with the same actual Cr3+ content, the luminous intensity of Cs2NaScCl6 synthesized by the improved solid‐phase synthesis is four times higher than the product synthesized by the hydrothermal method. an efficient Cl−‐Cr3+ charge transfer sensitization facilitated by localized electrons in [CrCl6]3− octahedron is the mechanism for the strong NIR emission of Cr3+ is proposed. Calculations based on density functional theory and Bader charge analysis support the notion that electrons in [CrCl6]3− octahedrons are strongly localized in Cs2NaScCl6:Cr3+, which is conducive to the Cl−–Cr3+ charge transfer process, resulting the internal quantum efficiency of 100% and external quantum yield as 42.3%. The highly efficient ultra‐broadband NIR emission with excellent stability offers many opportunities for applications in the field of NIR night vision and bio‐imaging.

New insights into the formation mechanism of the multicomponent carbides (Nb, M)C (M = Ti, Cr and Mn)

Combining first-principles calculations and classical nucleation theory, the results of elemental doping on the structure, electrons and stability of niobium carbides are investigated. Ti, Cr and Mn doping altered the physical characteristics of the carbides, resulting in lower mismatch strains and interfacial energies between the carbide and the substrate. Elemental doping reduced the critical nucleation size of carbides and contributed to the promotion of carbide nucleation. However, excessive doping with Cr and Mn increases the formation energy of carbides and unfavorable to carbide stabilization. Therefore, Cr and Mn are involved in the early elemental aggregation of carbides, while Ti and Nb are the main carbide-forming elements. The nano-precipitated phases of various compositions produced in niobium microalloyed steel were experimentally validated utilizing transmission electron microscopy (TEM) and three-dimensional atom probe tomography (3D-APT). The carbides primarily composed of Nb, Ti and C elements, with the presence of Cr and Mn in the core region leading to the formation of a core-shell structure, which is consistent with theoretical calculations.

Effect of chromium doping on the band gap tuning of titanium dioxide thin films for solar cell applications

A simple and inexpensive spray pyrolysis deposition (SPD) approach was used to produce TiO2 and Cr (2–8) at.%-doped TiO2 thin films. To explore the morphological features of the films, FE-SEM micrographs were used and found that 6 and 8 at.% TiO2:Cr films had fibrous patterns with diameters of 0.45 and 0.78 μm, respectively, while the remainder of the films were agglomerated particles. From X-ray diffraction investigation, it was found that the TiO2 thin films had an anatase crystal phase (tetragonal) up to 6 at.% Cr doping, while an anatase-rutile mixed crystalline phase was identified for 8 at.% Cr doping. The crystallite size of the pristine TiO2 film was 35 nm, while for TiO2:Cr films, it ranges from 35 to 46 nm. The Fizeau fringes technique was employed to measure the thickness of the TiO2 film and 165 nm was found for pristine TiO2 and 164–180 nm for TiO2:Cr films. UV–visible spectroscopy was used to study optical properties such as absorbance, refractive index, optical band gap, dielectric constant, and optical conductivity. As the Cr concentration increases, the optical band gap decreases from 3.40 eV to 2.70 eV. Using the four-point probe method, it was found that the resistivity changes with temperature and is also affected by the Cr content.

Synergistic effects of co-doping and rGO reinforcement to boost the structural, electrical, optical, and photocatalytic properties of manganese ferrite

In this study, using a co-precipitation method, MnFe2O4 spinel ferrite nanoparticles (NPs) doped with chromium and copper have been synthesized. Additionally, we have prepared nanocomposites (NCs) by incorporating 10 % reduced graphene oxide (r-GO) through ultra-sonication. This research investigates the influence of Cr and Cu doping and the addition of r-GO on different physicochemical properties, including structural characteristics, electrical behavior, and photocatalytic performance. Fabricated materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and Raman scattering. According to the structural study, Cr & Cu doped and rGO-reinforced MnFe2O4 spinel ferrite was formed successfully. The electrical conductivity of the ferrite nanocatalyst increased with Cr and Cu doping and r-GO addition. The BET surface area measurements for the bare, co-doped, and composite materials yielded 68 m2g-1, 94 m2g-1, and 139 m2g-1, respectively. The MnFe2O4/r-GO nanocomposite showed a notable aptitude for photo-degradation of RhB dye, achieving a degradation rate of around 98.48 % during 50-min duration under sunlight irradiation. The bare and co-doped equivalents exhibited deterioration rates of 39.86 % and 61.27 %, respectively. The photocatalyst is stable, losing just 1.27 % of its activity after five reusability tests. Scavenging radical results show that the hydroxyl (OH•) and e−/h + species are mainly involved in the degradation of RhB dye. MnFe2O4/r-GO NCs' highly porous texture, low band gap, larger surface area, and well-conducting nanosheets enhance dye degradation, making the composite material a promising environmental remediation material.

Effect of Cr substitution on nickel spinel ferrite’s surface morphology, structure, antibacterial activity and magnetic properties

This study reports the sol–gel auto-combustion (SGACT) synthesis of Cr-substituted NiFe2O4 nanoferrites with a composition, of CrxNi(1−x)Fe2O4 (where x = 0.000, 0.025, 0.050, 0.100, 0.150, 0.200), and it examines the effects of chromium on spinel ferrite’s structure and properties. The doping of Cr at the nickel site is first reported in the present study. The computed crystallite size “t” from the XRD results was found in the range of 34.2–40.4 nm, whereas, FESEM plots show larger-sized grains due to the aggregation of a large number of crystallites for the produced nanoferrites. Maximum saturation magnetization of 42.44 emu/g was attained by the Cr0.050Ni0.950Fe2O4 (x = 0.050) specimen, whereas, the Cr0.200Ni0.800Fe2O4 (x = 0.200) specimen attains the maximum coercivity in the current study. All these excellent values of magnetic parameters make our SGACT-produced nanoferrites useful for magnetic recording media applications. In S. aureus, Cr0.200Ni0.800Fe2O4 nanoparticles showed the highest zone of inhibition (ZOI) whereas, Cr0.050Ni0.950Fe2O4 nanoparticles showed the least ZOI. On the other hand, in E. coli, Cr0.850Ni0.150Fe2O4, Cr0.200Ni0.800Fe2O4 and Cr0.050Ni0.950Fe2O4 nanoparticles showed good ZOI. This makes our developed nanoferrites beneficial for biological applications as antibacterial agents.

Synthesis of new oxygen deficient triple layered perovskite oxides LaSr3Fe3-xCrxO10-δ (x = 0.0, 0.2, and 0.5): Structural, optical, magnetic and photocatalytic properties

In the present study, new oxygen deficient triple layered Ruddlesden-Popper (RP) phases LaSr3Fe3-xCrxO10-δ (x = 0.0, 0.2, and 0.5) have been prepared via sol-gel procedure. The prepared n = 3 RP phases were characterized with various characterization techniques in order to visualize the effect of Cr3+ doping on structural, optical, magnetic and photocatalytic properties. Rietveld structural refinements showed that all the phases crystallized in the I4/mmm space group with tetragonal symmetry. Dominant anti-ferromagnetic (AFM) interactions (Fe3+―O―Fe3+ and Fe4+―O―Fe4+) were noticed in each of these oxygen deficient triple layered phases with presence of weak ferromagnetic (FM) interactions. The decline in the values of Neel temperature (TN) with Cr doping has been interpreted on the basis of increase in FM Fe3+―O―Cr3+ interactions. The energy band gap values (Eg) of all the synthesised oxygen deficient phases vary from 1.63 to 1.73 eV, which makes them excellent photocatalysts for dye decontamination. Furthermore, the photocatalytic performance of the prepared phases was assessed by utilizing rhodamine B (RhB) dye as model dye pollutant. It was found that LaSr3Fe2.5Cr0.5O9.17 photocatalyst showed excellent results in the removal of RhB dye. As a result, we were further encouraged to extend the degradation to some other organic dyes such as methylene blue (MB), methyl orange (MO) and their mixture (RhB + MB + MO).

Boosting Alkaline Seawater Oxidation of CoFe-layered Double Hydroxide Nanosheet Array by Cr Doping.

The pursuit of stable and efficient electrocatalysts toward seawater oxidation is of great interest, yet it poses considerable challenges. Herein, the utilization of Cr-doped CoFe-layered double hydroxide nanosheet array is reported on nickel-foam (Cr-CoFe-LDH/NF) as an efficient electrocatalyst for oxygen evolution reaction in alkaline seawater. The Cr-CoFe-LDH/NF catalyst can achieve current densities of 500 and 1000mAcm-2 with remarkably low overpotentials of only 334 and 369mV, respectively. Furthermore, it maintains at least 100h stability when operated at 500mAcm-2.

Enhancing tribological performance of graphene sheet-embedded carbon films on steel substrates via texture engineering and chromium doping

Amorphous carbon (a-C) film is a promising solid lubricant coating due to its unique structure and excellent properties. However, its poor adhesion and long running-in period hinder the application in metal components. Graphene sheet-embedded carbon (GSEC) film has a significantly shorter running-in period but suffers from inferior tribological properties due to its rough surface and weak mechanical characteristics. In this study, we utilized an electron cyclotron resonance (ECR) plasma nano-surface manufacturing device to deposit GSEC films onto steel substrate surfaces. By manipulating the surface/interface texture and incorporating chromium (Cr) doping, the tribological properties of the GSEC films were improved both chemically and physically. The results demonstrated that the textured carbon film exhibited superior adhesion to the steel substrate and a wear life that was three orders of magnitude longer than the untextured GSEC film, under low normal load conditions while sliding against the GCr15-bearing steel ball. After doping the Cr into textured carbon films, there was a significant reduction in the friction coefficients, and the wear type of carbon film transformed from adhesive wear to abrasive wear. Moreover, the doped carbon films demonstrated prolonged wear lives under high normal loads. This improvement can be attributed to the formation of hard CrC nanocrystalline, which effectively reduced surface roughness and enhanced the mechanical properties of the carbon films. Notably, even under a contact pressure of 0.83 GPa, the doped carbon film maintained favorable tribological performances. These findings have extended the potential applications of carbon films on metal substrates.

Strengthening mechanism of Cr doping in Mo2FeB2-based cermets and effects on biphase interface

EDS, SEM, and TEM were utilized to investigate the effects of various Cr doping amounts on the microstructure and properties of Mo2FeB2-based cermets. The mechanism behind Cr doping and its influence on the biphase interfaces were elucidated by first-principle and EET theories, respectively. The results show that a moderate amount of Cr doped into Mo2FeB2-based cermets is preferentially solid-solved in the Mo2FeB2 hard phase, which leads to an enhancement in the wettability of the system, as well as an increase in the fracture toughness and transverse rupture strength (TRS) of the cermets. Excessive Cr addition leads to a decrease in mechanical properties due to coarser aggregation of hard phase particles and a decrease in the volume fraction of the binder phase. With increased Cr addition, a significant amount of Cr starts to solid-solve in the Fe-based binder phase when the saturation point for solid-solved Cr in the hard phase is approached. However, Cr solid-solved in the hard phase has the most pronounced effect on the mechanical properties of cermets. Combined with the first principle calculation, it can be seen that Cr tends to occupy the position of iron atoms when solid-solved in the hard phase, thus enhancing the covalent bonding in the system. Analysis of the valence electron structure at the interface reveals that adding a moderate amount of Cr increases the electron density and the number of atomic state groups at the interface. At this point, the interfacial stability and bond strength between the two phases are increased, which positively affects the mechanical properties of the cermets. Nevertheless, an excess of Cr is detrimental as it leads to a decrease in the ρ' and σN, thus affecting the bond strength at the interface.

Engineering room temperature multiferroicity and temperature dependent dielectric properties of Cr doped BaTiO3 ceramics

The coexistence of ferroelectricity, ferromagnetism, and piezoelectricity at room temperature in BaTi1-xCrxO3 (0 ≤ x ≤ 0.06) nanostructures is interesting and leads to the multiferroic nature of system. Sol-gel auto-combustion technique has been used for the synthesis of nanostructures. The XRD patterns along with Rietveld refinement analysis, confirm that the samples possess parent tetragonal perovskite structure in the P4mm space group. The oxygen vacancies stoichiometry ratio was estimated through XPS studies. The scanning electron microscopy (SEM) confirms the large grain size in the doped sample. The study of leakage current density reveals an increase in its value with the increase in Cr content due to defects induced in the system. P-E measurements confirm the ferroelectric nature of the samples that diminishes in the doped samples due to the high leakage current. Moreover, the estimated value of energy efficiency (η) was found to be maximum for the undoped sample. The undoped BaTiO3 has a diamagnetic character that is partially altered into weak ferromagnetic under the Cr-doping at the expense of decreasing polarization parameters. The temperature-dependent dielectric constant shows all characteristics of phase transitions in the samples. The doping of Cr enhances the ferroelectric to paraelectric phase transition temperature (Tc). The piezoelectricity remains preserved in the doped samples. Thus, the coexistence of ferroelectricity, ferromagnetism, and piezoelectricity at room temperature finalizes the multiferroic nature of the synthesized samples.

Identifying the photon absorption characteristics of Cr-doped Cu2ZnSnS4 (CZTS:Cr) thin film deposited by Co-sputtering technique

This study investigates the potential of a quaternary compound semiconductor to be realized as the absorber layer for third-generation intermediate band solar cells (IBSCs). In this work, the effects of Cr doping into Cu2ZnSnS4 (CZTS) host material to form intermediate band within the forbidden bandgap were studied. The films were deposited by a co-sputtering technique. It has been found that Cr has a high preference to substitute Zn, followed by Sn, then Cu. Insufficient Cr does not lead to intermediate band but, instead, forms defect states within the bandgap. Excess Cr however deteriorates CZTS (112) peak while at the same time secondary phase of cubic-ZnCr2S4 starts to grow. At sufficient levels of Cr content, absorption coefficient tremendously improved to 105 cm−1, resulting in an additional absorption peak attributed to possible formation of an intermediate band. This intermediate band is located at 1.40 ± 0.02 eV below CBM, while the band gap Eg is 1.55 eV. Further optimization to the sulphurization process reveals that the intermediate band peak, ECIL could be adjusted towards blue or red shift by manipulating Cr and/or sulphur content. This yields a bandgap of 1.52 eV with two intermediate bands positioned at 0.90 eV and 1.20 eV above the VBM. These preliminary findings are beneficial prior to realizing a working device of CZTS:Cr intermediate band solar cell.

Investigation physical properties of sprayed Cr doped ZnO thin films

ZnO and ZnO:Cr films were grown by the chemical spray deposition (CSD). The effect of the Cr content on ZnO was studied. All ZnO films show polycrystalline, hexagonal wurtzite structure, with (002) dominant plane. AFM displayed that films have a compact surface, its root mean square roughness increased with Cr percentage. The average diameter was smaller than 64 nm. The optical bandgap was evaluated using Transmittance data. Their values were found to be decreases via increment in Cr doping.

Tailoring the structural, magnetic and dielectric properties of cobalt ferrites by chromium substitution

Ferrites are renowned for their extensive use in a variety of industries, from manufacturing to the biomedical field. In the current study chromium substituted cobalt ferrite nanoparticles (CoCrxFe2-xO4,x = 0, 0.25, 0.5, 0.75, and 1) were synthesized by utilizing the sol–gel auto combustion method. Various analytical tests confirm the effect of Cr doping concentration on cobalt ferrites. The structural and morphological analysis of samples were done using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) respectively. The samples' pure spinel structure was confirmed by XRD analysis. Magnetic characterization at room temperature and low temperature were carried out using Quantum Design's PPMS. The dielectric properties of the samples were examined using a Hioki 3532 LCR hitester. The results demonstrate the effect of chromium substitution in cobalt ferrites and suggest the possible uses of the prepared samples.