Effect Of Cr Doping Research Articles

Effects of Zn-Cr-substitution on the structural and magnetic properties of Ni1−xZnxFe2−xCrxO4 ferrites

Cr and Zn-substituted nickel ferrites, general formula Ni1−xZnxFe2−xCrxO4 (x=0, 0.1, 0.3, 0.5, 0.7), were prepared using the sol-gel auto-combustion method. For precise analysis, the Ni1−xZnxFe2O4and NiFe2−xCrxO4 (x=0, 0.1, 0.3, 0.5, 0.7) samples were also checked individually. The effects of Cr and Zn doping on the structural, morphological, and magnetic properties of the samples were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The full pattern fitting of Rietveld method using MAUD program was also applied to determine the exact coordinates of the atoms, unit cell dimensions, and ion occupancy. XRD measurement by Rietveld refinement confirmed the crystalline structure and phase purity of all the ferrites. SEM images showed that the particles were in the nanosize range. VSM results revealed that the values of MS in the NiFe2−xCrxO4 samples decreased and that HC had no regular behavior with increasing Cr content. The maximum value of HC=16Oe was obtained for a Cr content of x=0.7. On the other hand, saturation magnetization values initially increased in both the Ni1−xZnxFe2−xCrxO4 and Ni1−xZnxFe2O4 samples, with changing the doping level up to x=0.3, while for further content, MS decreased. In addition, coercivity decreased with increasing doping level.

Effects of Cr-doping on the electronic transport properties in antiperovskite nitrides Mn3−xCrxZnN (0≤x≤0.5)

Antiperovskite intermetallic Mn3−xCrxZnN (0≤x≤0.5) compounds have been prepared to study the Cr doping effect on the electronic transport properties. The temperature dependent resistivity ρ(T) for x≤0.3 shows notable and broader slope change. Meanwhile, with increasing Cr doping, the slope change shifts to lower temperatures and is gradually suppressed for x>0.3. For x=0.0 and 0.5, the measurements of magnetization from 10K to 350K reveal that Mn3−xCrxZnN compounds go through a transition from the dominant AFM interactions to one where the FM and AFM interactions coexist. For low-temperature region (15–80K), the electron–electron scattering is dominant, and the number of phonons abruptly increases with increasing temperature. Small polaron hopping model (SPH) is used to understand the temperature dependence of electrical resistivity in the high-temperature range of 200–300K and a clear decrease of the polaron activation energy was observed for x≤0.2. The residual resistivity ratio (RRR) decreases while the residual resistivity increases (ρ0) with increasing Cr-doping level. The maximum total entropy change (ΔSmax) decreases by increasing the Cr doping from x=0.0 to 0.2.

Si and Cr Doping Effects on Growth and Mechanical Properties of UltrananocrystallineDiamond/Amorphous Carbon Composite Films Deposited on Cemented Carbide Substrates by Coaxial Arc Plasma Deposition

Si and Cr Doping Effects on Growth and Mechanical Properties of UltrananocrystallineDiamond/Amorphous Carbon Composite Films Deposited on Cemented Carbide Substrates by Coaxial Arc Plasma Deposition

Cr modified Raman, optical band gap and magnetic properties of SnO2 nanoparticles

Pure and Cr (1, 3, 5, 7 and 10 at.%) doped SnO2 nanoparticles were synthesized in aqueous solution by a low cost chemical co-precipitation method without using any stabilizing agent. The effects of Cr doping on Raman, optical band gap and magnetic properties of SnO2 nanoparticles were investigated. Particle size is found to decrease with Cr doping into the SnO2 matrix which was confirmed by TEM. Besides of the fundamental mode of vibration, two additional peaks are also observed in Raman spectra which are correlated to Cr. The absorption spectra showed two peaks at 340 and 454 nm. The absorbance peak at 340 nm is assigned to the transition from valence band (VB) to conduction band (CB) and the peak at 454 nm was due to the transition from VB to mid gap energy level introduced by Cr. The optical band gap of undoped SnO2 nanoparticles is calculated to be 3 eV. With the doping of Cr in SnO2, band gap increases due to the decrease in particle size. The emission intensity is found to decrease with the increase in Cr doping due to the emission from CB to mid gap energy levels introduced by Cr between CB and VB. Undoped SnO2 nanoparticles show room temperature ferromagnetism due to the presence of defects and oxygen vacancies. The heavily doped SnO2 nanoparticles show paramagnetic nature due to the antiferromagnetic coupling between Cr and its nearest neighbour.

Effect of Mn and Cr doping on the up-conversion luminescence from NaYF4:Yb3+,Er3+

The up-conversion luminescence where the absorption of two or more low-energy photons results in emission of a higher-energy photon has been highly effective in certain applications such as bioanalytical assays. Currently one of the most efficient up-converting materials is the NaYF4:Yb3+,Er3+. However, some applications (e.g. solar cells) still require improvement of the up-conversion efficiency in order to have actual practical use. Therefore, it is important to enhance the performance of the materials. In this work, the effect of Mn and Cr doping on the up-conversion luminescence of NaYF4:Yb3+,Er3+ was studied. The materials were prepared using the co-precipitation method and the ratios of the doping ions were optimized for best up-conversion intensity. The as-prepared materials showed very similar sizes and morphologies. Cr co-doping was observed to increase the up-conversion luminescence whereas the addition of Mn resulted in quenching. Up-conversion luminescence was also measured with different excitation power densities and the results suggested that Cr co-doping enables the up-conversion in lower power densities than without Cr co-doping. Furthermore, the reasons for the changes in up-conversion luminescence intensity were discussed.

Competition between ferromagnetic and antiferromagnetic interactions by Cr doping at Mn sites in antiperovskite Mn3−xCrxZnN (0≤x≤0.5) compounds

The Cr doping effect on the lattice and magnetic properties in Mn3−xCrxZnN was reported in the antiferromagnetic intermetallic host material Mn3ZnN. The lattice parameter decreases with the increase of the Cr concentration. Measurements of magnetization from 10K to 350K reveal that sharp antiferromagnetic (AFM)-to-paramagnetic (PM) transitions of the host material exist at 185K (ZFC) and 177K (FC). The peak is broadened clearly as the Cr doping was increased and when the Cr concentration exceeded 0.3, a significant ferromagnetic (FM) character was found to coexist with an AFM phase. At x=0.4 and 0.5, the M–H curves exhibit small magnetic hysteresis loop, indicating the dominant FM interactions in these samples. Also, a positive value of Weiss Temperature (ΘW) at x=0.5 in H/M–T plot suggests that the FM interaction is dominant when the Cr doping increases.

Possibility of martensite transition in Pt–Y–Ga (Y=Cr, Mn, and Fe) system: An ab-initio calculation of the bulk mechanical, electronic and magnetic properties

Using first principles calculations based on density functional theory we have studied the effects of Fe and Cr doping at the Mn site on mechanical, electronic, and magnetic properties of Pt2MnGa and Ni2MnGa. We predict on the basis of formation energy that all the substituted X2Mn1−xYxGa alloys (x=0.00, 0.25, 0.75, 1.00; X=Pt, Ni; Y=Fe and Cr) are stable materials. Further, all the substituted materials which we have studied here are likely to undergo martensite transition. In this work, we have reported how the stability of the austenite and martensite phase varies with the extent of substitution by Fe as well as Cr at the Mn site. Further, we study the bulk mechanical properties of the austenite and martensite phases of the stoichiometric systems only. We observe that Pt-based systems are inherently much less brittle in comparison to the Ni-based systems studied here. We also study the magnetic properties. Interestingly, contrary to the unsubstituted case as well as the case when Mn is substituted by Fe, the substitution by Cr at the Mn site leads to lowering of energy in case of an intra-sublattice anti-ferromagnetic configuration compared to the ferromagnetic configuration.

Investigating Orbital Magnetic Moments in Spinel-Type MnV2O4 Using X-ray Magnetic Circular Dichroism

Element-specific magnetic structures, particularly orbital magnetic moments, of spinel-type MnV2O4 were investigated using X-ray magnetic circular dichroism (XMCD). X-ray absorption and XMCD spectra clearly reveal that the Mn2+ (d5) and V3+ (d2) states are coupled antiferromagnetically. Analyses of XMCD spectra using magneto optical sum rules revealed that small but finite orbital magnetic moments remain in both V and Mn 3d states, which accounts for the antiferro-type orbital ordering in the V sites of MnV2O4 with coexisting complex and real orbital states. Additionally, the Cr doping effect in MnV2O4 was examined. The XMCD spectra of Cr 3+ (d3) L-edges exhibited the substitution of Cr ions to the V sites ferromagnetically, with low conductivity through the suppression of the orbital ordering.

Mitigating the voltage decay and improving electrochemical properties of layered-spinel Li 1.1 Ni 0.25 Mn 0.75 O 2.3 cathode material by Cr doping

Abstract Layered-spinel composite cathode material Li 1.1 Ni 0.25 Mn 0.75 O 2.3 and Cr doped Li 1.1 Ni 0.25−x Mn 0.75−x Cr 2x O 2.3 (x = 0.005, 0.015, 0.025) have been synthesized. The effect of Cr doping on physical and electrochemical properties are discussed using the characterizations of X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), charge/discharge, cyclic and rate tests. The results show that the Li 1.1 Ni 0.235 Mn 0.735 Cr 0.03 O 2.3 has the best electrochemical performance. Among the pristine and doped samples, the Li 1.1 Ni 0.235 Mn 0.735 Cr 0.03 O 2.3 shows the highest discharge capacity (261.9 mAhg −1 ), first coulomb efficiency (93.17%) and best rate performance (113 mAhg −1 at 10 C rates). Furthermore, the voltage decay of Li 1.1 Ni 0.25 Mn 0.75 O 2.3 can be mitigated after Cr doping effectively. The middle voltage (MDV) of Li 1.1 Ni 0.25 Mn 0.75 O 2.3 after 55 cycles is increased from 3.103 V to 3.220 V in Li 1.1 Ni 0.235 Mn 0.735 Cr 0.03 O 2.3 . Electrochemical impedance spectroscopy (EIS) results show that the R ct of Li 1.1 Ni 0.25 Mn 0.75 O 2.3 electrode decreases after Cr doping.

DFT study of the effects of interstitial impurities on the resistance of Cr-doped γ-Fe(111) surface dissolution corrosion.

Using density-functional calculations, we studied the interaction between interstitial impurities (N, C) and γ-Fe(111) surfaces doped, or not, with Cr, as well as the effect of Cr doping on the dissolution corrosion resistance of the γ-Fe(111) surface. The elementary processes studied afforded microscopic insights into the formation of a Cr-depleted zone, a phenomenon that leads to local corrosion of the stainless steel surface. The aim of this work was to study, at the atomic scale, the effects of N and C on the segregation behavior of Cr and the synergetic effect between co-doped atoms on the resistance to dissolution corrosion of austenitic stainless steel surfaces. The results showed that interstitial impurities prefer to be trapped at near-surface sites, which can impact the segregation behavior of Cr such that it shifts from the surface to the subsurface. Electrode potential calculations and density of states analysis demonstrated that doping with Cr or inserting interstitial impurities into the solid solution can improve the surface corrosion resistance of an fcc Fe substrate, but detrimental effects on the surface corrosion resistance are induced by interactions between Cr and interstitial impurity atoms in co-doped surfaces. The formation of near-surface Cr carbides and nitrides (speculated to be Cr2N and Cr23C6 due to the results obtained for particular co-doped surfaces) was also noted. The results of our theoretical calculations explain some of the experimental results observed at the atomic scale.

Studies on magneto-resistance, magnetization and thermoelectric power of Cr substituted La0.65Ca0.35Mn1−xCrxO3 (0≤x≤0.07) manganites

A systematic investigation has been carried out on effect of Cr-doping on structural, magneto-resistance, magnetic and thermoelectric power properties of La0.65Ca0.35Mn1−xCrxO3 compounds. Samples were prepared using conventional solid state reaction method. The XRD analysis using Rietveld refinement reveals that the samples are single phased. Temperature dependent electrical resistivity measurements show the existence of the expected metal–insulator transition (TMI) which is followed by a small hump at temperatures lower than TMI. With the application of magnetic field, resistivity of all the samples is found to decrease and TMI is observed to shift towards higher temperature. This is attributed to induced magnetic ordering of the localized t2g spins and increased electron transfer integral between Mn3+/Mn4+ via oxygen by the application of magnetic field. MR% is observed to increase with the increasing Cr concentration. Magnetic studies show that the Curie temperature, TC and magnetic moment decreases with Cr-content which is consistent with the electrical studies. Electrical resistivity and thermoelectric power data have been analyzed using theoretical models and both suggest that the small polaron hopping (SPH) model is operative in the high temperature insulating region for the entire series of samples.

Investigation of Cr0.06(Sb4Te)0.94 alloy for high-speed and high-data-retention phase change random access memory applications

The effects of Cr doping on the structural and electrical properties of Crx(Sb4Te)1−x materials have been investigated in order to solve the contradiction between thermal stability and fast crystallization speed of Sb4Te alloys. Cr0.06(Sb4Te)0.94 alloy is considered to be a potential candidate for phase change random access memory (PCM), as evidenced by a higher crystallization temperature (204 °C), a better data retention ability (137.6 °C for 10 years), a lower melting point (558 °C), a lower energy consumption, and a faster switching speed in comparison with those of Ge2Sb2Te5. A reversible switching between set and reset states can be realized by an electric pulse as short as 5 ns for Cr0.06(Sb4Te)0.94-based PCM cell. In addition, Cr0.06(Sb4Te)0.94 shows good endurance up to 1.1 × 104 cycles with a resistance ratio of about two orders of magnitude.

Effect of Cr doping on ferroelectric and magnetic properties of Bi0.8Ba0.2FeO3

Multiferroic ceramics Bi0.8Ba0.2Fe1−xCrxO3 (x=0, 0.05 and 0.1) were synthesized by using the conventional solid state reaction method. The pure phase with rhombohedral structure was confirmed by the X-ray diffraction measurements for all samples. It was shown that the magnetic and the ferroelectric properties were simultaneously improved, and the maximum values of the remnant magnetization (2Mr) and the remnant polarization (2Pr) at room temperature for all samples are around 1emu/g and 1.9μC/cm2, respectively. Furthermore, the leakage current density, the low frequency dispersion in the dielectric constant and the dielectric loss decreased with increasing the Cr concentration from x=0 to 0.1. A remarkable change in the P–E loop was observed whether a bias dc magnetic field was applied or not, approving the existence of the magnetoelectric coupling indirectly therein.

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures

Enhanced magnetic and ferroelectric properties in Cr doped Bi2Fe4O9 ceramics

Single phase Bi2Fe4(1−x)Cr4xO9 (0 ≤ x ≤ 0.08) ceramics are prepared by a modified Pechini method to investigate the effect of Cr doping on magnetic and ferroelectric properties. The results show that both the magnetic and ferroelectric properties are strongly dependent on Cr doping. With the introduction of Cr ions, Bi2Fe4O9 ceramics change from antiferromagnetism to weak FM at room temperature, in accompaniment with the enhancement of ferroelectric properties. The remnant magnetization and polarization enhance monotonically from 0.014 emu/g and 0.103 μC/cm2 for x = 0.02 sample to 0.025 emu/g and 0.53 μC/cm2 for x = 0.08 sample, respectively. The improvement of magnetic and ferroelectric properties should be mainly related to the suppression of inhomogeneous magnetic spin structure and the reduction of electric leakage by Cr doping. These results suggest that Cr doping can adjust the magnetic and ferroelectric properties of Bi2Fe4O9 ceramics, which is a promising candidate for room temperature multiferroics.

Effect of Cr doping on the structural, morphological, optical and electrical properties of indium tin oxide films

We report on the preparation and characterization of high-purity chromium (0.5–2.5 at.%)-doped indium tin oxide (ITO, In:Sn = 90:10) films deposited by sol–gel-mediated dip coating. The effects of different Cr-doping contents on structural, morphological, optical and electrical properties of the films were characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), UV–Vis spectroscopy and four-point probe methods. XRD showed high phase purity cubic In2O3 and indicated a contraction of the lattice with Cr doping. FESEM micrographs show that grain size decreased with increasing the Cr-doping content. A method to determine chromium species in the sample was developed through the decomposition of the Cr 2p XPS spectrum in Cr6+ and Cr3+ standard spectra. Optical and electrical studies revealed that optimum opto-electronic properties, including minimum sheet resistance of 4,300 Ω/Sq and an average optical transmittance of 85 % in the visible region with a band gap of 3.421 eV, were achieved for the films doped with Cr-doping content of 2 at.%.

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures

Effect of Cr and Fe Doping on the Structural and Optical Properties of ZnO Nanostructures