Influence Of Transition Metal Research Articles

Oxidation mechanism and mechanical properties of substitutional transition metal modified Nb4AlC3: A first-principles density functional theory study

The MAX phase, Nb4AlC3, has been identified as a potential candidate for high-temperature structural materials, but its inherent limitations, including poor oxidation resistance, low Young's modulus, and low hardness, have hindered its widespread application. To address these fundamental questions, in this paper, the oxidation mechanism of Nb4AlC3 with and without the influence of transition metal (TM) elements is thoroughly investigated through systematic quantum mechanical calculations. The investigation considers six possible O doping sites in the Nb–Al/C layer, and the calculation results reveal a tendency for O to occupy the hexahedral Site-Ⅱ. This can be mainly attributed to the strong charge interaction between O and Nb, Al. Furthermore, the study explores the impact of all “M" site TM elements on the compound's oxidation resistance. Zr and Mo are identified as representatives that can enhance or weaken the oxidation resistance, respectively. Subsequently, the effects of Zr doping on the phase stability, mechanical properties, lattice thermal conductivity, and electronic properties of Nb4AlC3 were examined. The findings reveal that all (Nb1-xZrx) 4AlC3 compounds are thermodynamically stable, elastically stable, and brittle materials with good thermal conductivity. Among them i, Young's modulus and hardness increase the most when the Zr content is low (0.125) compared to the parent phase, which aligns with the available experimental results. And the system with 0.125 Zr content has the highest high-temperature stability (1300 K). Therefore, as expected, Zr doping can improve the comprehensive properties of Nb4AlC3 to some extent.

Effect of transition metal and alkali oxides on structural, optical and dielectric properties in Zinc-Phosphate amorphous glassy systems

The influence of transition metal and alkali earth metal oxide on the structural, optical and dielectric properties of inorganic glasses prepared by melt quenching method, having chemical composition 0.35ZnO0.25P2O5-(0.4-x) Na2O-xV2O5 (0.05≤x≤0.25), have been studied. The Rietveld Refinement of the XRD spectra confirms the presence of Na3P8VO23 and Zn2V2O7 nanocrystallites. Raman spectroscopy has been deployed to identify and quantify the individual phases present within the glass matrix. The optical bandgap energy values, which are obtained from the UV–Vis spectra, vary with V2O5 concentration (x), and an inverse association between the optical bandgap and Urbach energy has been demonstrated. The absorbance and reflectance spectra have been investigated, and several optical parameters, such as the excitation and absorption coefficients, refraction index, polarizability, SELF and VELF functions, etc., have also been examined. The dielectric constant and dielectric loss decrease with the increase in frequency but increase with the rising temperature. The dielectric properties have been examined at various temperatures and frequencies. The analysis of the scaling property of electric modulus indicates the conductivity or dielectric relaxation mechanisms, which is temperature independent and composition-dependent. The estimated value of the exponent parameter from Bergman's function being less than unity confirms the non-Debye type relaxation process occurring within the transition metal and alkali oxide doped zinc-phosphate glass matrix.

Influence of transition metal on the mechanical and electronic properties of RuB2 from first-principles calculations

The influence of transition metals on the mechanical and electronic properties of RuB2 is studied by the first-principles approach. The results show that the TM-doped RuB2 is a thermodynamic stability. Naturally, the stability of TM-doped RuB2 is related to the hybridization between atoms. The transition metals enhance the electronic properties of RuB2. We find that these transition metals enhance the hardness, shear deformation resistance and elastic stiffness of RuB2. The hardness of Cr-doped RuB2 is 26.8GPa, which is larger than the RuB2. The improvement of hardness derives from the hybridization between B atoms under the role of metals.

The influence of transition metal (Mn, Fe, Co, Cu) doping on the electronic and vibrational properties of indium nitride nanocage: A DFT study

Density functional theory (DFT) method is used to analyse the electronic and vibrational properties of an indium nitride (InN) Nanocage doped withtransition metals(TMs). To investigate the impact of doping, an Indium atom is replaced with a TM atom (Mn, Fe, Co, and Cu) to produce transition metal doped Nanocages. According to present study, these transition metal doped indium nitride Nanocages are remarkably stable, and their HOMO-LUMO energy gaps are significantly lower than the pristine In12N12 Nanocage. To study the electronic property in details global reactivity descriptors such as hardness, ionisation potential, electron affinity and electrophilicity are calculated. Vibrational frequency analysis ensures that all the structures are real minima on the potential energy surface that means they are dynamically stable. The IR and Raman spectra reported here are intended to provide chemical insight into the characterization of these unidentified structures, allowing for further experimental study.

Influence of transition metal on the mechanical and thermodynamic properties of IrAl thermal barrier coating

Although IrAl is a fascinating thermal barrier coating, the improvement of overall performances of IrAl coating is still a big challenge. Here, we apply the first-principles calculations to study the influence of alloying elements on the Vickers hardness, elastic and thermodynamic properties of IrAl coating. Five alloying elements: Cr, Nb, Mo, W and Re are considered. The results show that these elements are stable in IrAl coating. The Re-doped IrAl is more thermodynamic stability than the TM-doped IrAl. The Vickers hardness of Cr-dopant and Re-dopant is 13.2 GPa and 13.4 GPa, respectively, which are larger than the IrAl coating. The Debye temperature of Cr-dopant and Re-dopant is 433.5K and 428.2K, which are also larger than the IrAl coating. The high mechanical properties are that these elements (Cr and Re) improve the localized hybridization between Ir and Al. Hence, we believe that alloying elements of Cr and Re not only enhance the mechanical properties but also improve the thermodynamic properties of IrAl coating.

First principle study of influence of transition metal (Cr, Mn, Fe, Co) doping on magnetism of TiO<sub>2</sub>

It is still in controversy whether the transition metal doped TiO<sub>2</sub> will generate room temperature ferromagnetism and where its magnetism originates from. In order to solve this problem, in this paper we use the GGA+U method based on density functional theory to conduct a first-principle study of the magnetic and optical properties for each of the systems of Ti<sub>0.875</sub><i>X</i><sub>0.125</sub>O<sub>2</sub>, <i>X </i>= Cr, Mn, Fe, Co. We calculate the ground state energy of each system, on the supposition that they are ferromagnetic or antiferromagnetic. After comparison, the ferromagnetic state is speculated to be its ground state. The binding energy and magnetism calculation results show that Ti<sub>0.875</sub>Cr<sub>0.125</sub>O<sub>2</sub> has the best stability in all doped systems, that the transition metal element doped TiO<sub>2</sub> system has a net magnetic moment, and that the doped systems are ferrimagnetic. In comparison, the net magnetic moment produced by Cr, Mn and Fe doped with TiO<sub>2</sub> are substantial, showing that these three systems have good ferromagnetic properties. The Curie temperatures of all doped systems are above room temperature, which is of great significance for the electron spin to retain the information in dilute magnetic semiconductors (DMS), and also greatly helps with the practical application of magnetic materials. The analysis of the energy band structure reveals that intrinsic TiO<sub>2</sub> is non ferromagnet, Ti<sub>0.875</sub>Cr<sub>0.125</sub>O<sub>2</sub> and Ti<sub>0.875</sub>Mn<sub>0.125</sub>O<sub>2</sub> maintain semiconductor properties, and Ti<sub>0.875</sub>Fe<sub>0.125</sub>O<sub>2</sub> and Ti<sub>0.875</sub>Co<sub>0.125</sub>O<sub>2</sub> exhibit metal characteristics. The doped systems produce room temperature ferromagnetism, the main magnetic source is the transition metal elements (Cr, Mn, Fe, Co) 3d electron orbit induced polarization of the surrounding O-2p state spin electrons, causing the systems to produce a net magnetic moment and be ferromagnetic. The absorption spectrum of the doped system is red-shifted, which shows that the doping causes the range of its absorption spectrum to extend to the visible range. At the same time, in all the doped systems in this article, Fe and Co doped TiO<sub>2</sub> have the best light absorption intensity, and the magnetic property of the Fe doped system is the strongest, which indicates that when the system is ferromagnetic, the spin up and spin down splitting will occur in the local magnetic field, which will change the electronic structure of TiO<sub>2</sub> and enhance its photocatalytic performance. The calculation results in this paper are of theoretical significance for preparing TiO<sub>2</sub> with curie temperature above room temperature by <sub>being doped</sub> with transition metal elements of Cr, Mn, Fe, and Co.

Adsorption of H2O molecule on TM (Au, Ag) doped-MoS2 monolayer: A first-principles study

The influence of transition metal (TM) atoms (Au, Ag) doping on the structure parameters and electronic properties of MoS2 monolayer was studied based on DFT calculations. In order to realize the adsorption mechanism, the adsorption structures, adsorption energy, charge transfer, density of states (DOS), and electron density difference of water (H2O) molecule absorbed on two kinds of doped-MoS2 monolayer were analyzed. The results show that the electronic properties of TM (Au, Ag) doped-MoS2 monolayer have significantly changes and the chemical activity is obviously enhanced compared with the MoS2 monolayer. Moreover, Au or Ag doped-MoS2 monolayer both exhibits excellent adsorption capacity to H2O molecule and the processes of absorption both are chemical.

Electronic Structure and Visible-Light Absorption of Transition Metals (TM=Cr, Mn, Fe, Co) and Zn-Codoped SrTiO3: a First-Principles Study**Supported by the National Natural Science Foundation of China under Grant No 51474011, the Postdoctoral Science Foundation of China under Grant No 2014M550337, and the Key Technologies R&D Program of Anhui Province of China under Grant No 1604a0802122.

First-principles calculations are performed on the influence of transition metal (TM=Cr, Mn, Fe, Co) as codopants on the electronic structure and visible-light absorption of Zn-doped SrTiO3. The calculated results show that (Zn,Mn)-codoped SrTiO3 requires the smallest formation energy in four codoping systems. The structures of the codoped systems display obvious lattice distortion, inducing a phase transition from cubic to rhombohedral after codoping. Some impurity Cr, Mn and Co 3d states appear below the bottom of conduction band and some Fe 3d states are located above the top of valence band, which leads to a significant narrowing of band gap after transition metal codoping. The enhancement of visible-light absorption are observed in transition metals (TM=Cr, Mn, Fe, Co) and Zn codoped SrTiO3 systems. The prediction calculations suggested that the (Zn,Mn)- and (Zn,Co)-codoped SrTiO3 could be the desirable visible-light photocatalysts.

Influence of Transition Metal and Synthesis Methodology on the Active Site Density on the Surface of PGM-Free Catalysts

State-of-the-art polymer electrolyte fuel cells (PEFCs) utilize platinum (Pt) or Pt-alloy nanoparticles supported on high surface-area carbon as catalysts for oxygen reduction reaction (ORR) at the PEFC cathode.1 Platinum group metal-free (PGM-free) catalysts have the potential to reduce the high PEFC cost by replacing Pt with far less expensive materials. Over the past two decades, the growing interest in PGM-free catalysts has led to significant improvements in their performance, which is now approaching that of Pt-based catalysts.2–5 Several insights into the critical factors, such as the role of transition metal, catalyst precursors and pore-formers have been studied.3–5However, for further development of PGM-free catalyst understanding the nature of active site(s) in PGM-free catalysts, as well as the determination of the active site density and turnover frequency (TOF) are vital. PGM-free catalysts have little affinity to “standard” molecular probes, such as carbon monoxide and hydrogen sulfide, that effectively poison ORR active sites in PGM catalysts.6,7 Only recently, an ex situ and in situ method for reversibly probing the active sites and estimating the active site density has been proposed.8,9 Malko et al. showed that nitrogen-based molecular probes can poison the active site and then be reductively stripped off in a voltammetric scan.9 In this work, we have studied the effect of the transition metal and synthesis approach (type of precursor and catalyst fabrication method) on the active site. Active site density in catalysts derived from different transition metals was estimated using sodium nitrite (NaNO­2) as probe.9Figure 1a shows the reductive stripping curves for Los Alamos-developed Fe- and Co-derived CM-PANI-C catalysts, with Co exhibiting much higher affinity to the probe than Fe. The effect of different synthesis methodology and precursor with same transition metal was also studied. Reductive stripping of the probe from CM-PANI-Fe-C catalysts with and without Zn added as a pore former occurs at the same peak potentials suggesting the presence of identical active site in both cases (though occurring at a higher concentration in the catalyst synthesized using Zn). On the other hand, a catalyst with atomically dispersed Fe appears to bind the probe more strongly than CM-PANI-Fe-C catalysts (Figure 2b). Active site density estimation provides a quantitative assessment for the effect of the transition metal and synthesis methodology for further development of PGM-free catalyst. Acknowledgments This research is supported by DOE Fuel Cell Technologies Office, through the Electrocatalysis Consortium (ElectroCat). References S. Litster and G. McLean, J. Power Sources, 130, 61 (2004).H. T. Chung, J. H. Won, and P. Zelenay, Nat. Commun., 4, 1922 (2013).H. T. Chung et al., Meet. Abstr. MA2016-02, 2825 (2016).L. Lin, H. T. Chung, X. Yin, U. Martinez, and P. Zelenay, Meet. Abstr. MA2016-02, 2826 (2016).U. Martinez, E. F. Holby, J. H. Dumont, and P. Zelenay, Meet. Abstr. MA2016-02, 2827 (2016).Q. Wang, Z. Zhou, Y. Lai, Y. You, J. Liu, X. Wu, E. Terefe, C. Chen, L. Song, M. Rauf, N. Tian and S. Sun, J. Am. Chem. Soc., 136, 10882 (2014).7. D. Malko, T. Lopes, E. Symianakis, and A. R. Kucernak, J. Mater. Chem. A, 4, 142 (2016).N. R. Sahraie, U. I. Kramm, J. Steinberg, Y. Zhang, A. Thomas, T. Reier, J. Paraknowitsch and P. Strasser, Nat. Commun., 6, 8618 (2015).D. Malko, A. Kucernak, and T. Lopes, Nat. Commun., 7, 13285 (2016). Figure 1

Influence of transition metal on glass formability of Y–TM–B (TM = Fe, Ni) system

Semi-empirical Miedema’s model was combined with the geometric one to determine glass forming ability (GFA) of ternary Y–Fe–B and Y–Ni–B systems. The enthalpies of amorphous phase and solid solution were calculated, as well as the difference between both quantities which reflects the competition during solidification. Moreover, normalized mismatch entropy and glass forming ability parameter were also determined. According to the results, yttrium plays a dominant role due to the large atomic radius and highly negative heat of mixing with the most of alloying elements. The large radii of rare earth elements have been already known to be advantageous in glassy state formation. Enthalpy contour maps for investigated alloys are similar, but significant differences in absolute enthalpy values were observed. Nickel containing system possesses the highest glass forming ability in the wide range of compositions, comparing to Y–Fe–B and Y–Co–B ones.

Solid state synthesis of SrAl2O4:Mn2+ co-doped with Nd3+ phosphor and its optical properties

The optical properties of alkaline earth aluminates doped with rare earth ions have received much attention in the last years and this is due to their chemical stability, long-afterglow (LAG) phosphorescence and high quantum efficiency. However, there is a lack of understanding about the nature of the rare earth ion trapping sites and the mechanisms which could activate and improve the emission centers in these materials. Therefore a new phosphor material composition, SrAl2O4:Mn2+, co-doped with Nd3+ was synthesized by a traditional solid-state reaction method. The influence of transition metal and rare earth doping on crystal structure and its luminescence properties have been investigated by using X-ray diffraction (XRD), Raman scattering, Photoluminescence (PL) and Radioluminescence (RL). Analysis of the related diffraction patterns has revealed a major phase characteristic of the monoclinic SrAl2O4 compound. Small amounts of the dopants MnCO3 and Nd2O3 have almost no effect on the crsytalline phase composition. Characteristic absorption bands from Nd3+ 4f–4f transitions in the spectra can be assigned to the transitions from the ground state 4I9/2 to the excited states. The luminescence of Mn2+ activated SrAl2O4 exhibits a broad green emission band from the synthesized phosphor particles under different excitation sources. This corresponds to the spin-forbidden transition of the d-orbital electron associated with the Mn2+ ion. In photo- and radio-luminescence spectra, Nd3+ 4f–4f transition peaks were observed. The emitted radiations for different luminescence techniques were dominated by 560, 870, 1057 and 1335nm peaks in the visible and NIR regions as a result of 4I9/2→4G7/2 and 4F3/2→4IJ (J=9/2, 11/2 and 13/2) transitions of Nd3+ ions, respectively. Multiple emission lines observed at each of these techniques are due to the crystal field splitting of the ground state of the emitting ions. The nature of the emission lines is discussed.

Bulk diffusion induced structural modifications of carbon-transition metal nanocomposite films

The influence of transition metal (TM = V,Co,Cu) type on the bulk diffusion induced structural changes in carbon:TM nanocomposite films is investigated. The TMs have been incorporated into the carbon matrix via ion beam co-sputtering, and subsequently the films have been vacuum annealed in the temperature range of 300 – 700 °C. The structure of both the dispersed metal rich and the carbon matrix phases has been determined by a combination of elastic recoil detection analysis, x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The as-grown films consist of carbidic (V and Co) and metallic (Cu) nanoparticles dispersed in the carbon matrix. Thermal annealing induces surface segregation of Co and Cu starting at ≥ 500 °C, preceded by the carbide-metal transformation of Co-carbide nanoparticles at ∼ 300 °C. No considerable morphological changes occur in C:V films. In contrast to the surface diffusion dominated regime where all the metals enhance the six-fold ring clustering of C, in the bulk diffusion controlled regime only Co acts as a catalyst for the carbon graphitization. These results are consistent with the metal-induced crystallization mechanism in the C:Co films. The results are discussed on the basis of the metal-carbide phase stability, carbon solubility in metals or their carbides, and interface species.

Thermoelectric Properties of Co4Sn6Se6 Ternary Skutterudites

A ternary ordered variant of the skutterudite structure, the Co4Sn6Se6 compound, was prepared. Polycrystalline samples were prepared by a modified ceramic method. The electrical conductivity, the Seebeck coefficient and the thermal conductivity were measured over a temperature range of 300–800 K. The undoped Co4Sn6Se6 compound was of p-type electrical conductivity and had a band gap E g of approximately 0.6 eV. The influence of transition metal (Ni and Ru) doping on the thermoelectric properties was studied. While the thermal conductivity was significantly lowered both for the undoped Co4Sn6Se6 compound and for the doped compounds, as compared with the Co4Sb12 binary skutterudite, the calculated ZT values were improved only slightly.

Influence of transition and heavy metal ions on ATP-ases activity in rat synaptic plasma membranes

The influence of transition metal (Cu2+, Zn2+, Fe2+ and Co2+) and heavy metal ions (Hg2+, Pb2+ and Cd2+) on the activities of Na+/K+-ATPase and Mg2+-ATPase isolated from rat synaptic plasma membranes (SPM) was investigated. The aim of the study was to elucidate the inhibition of both ATPase activities by exposure to the considered metal ions as a function of their affinity to bind to the ?SH containing ligand L-cysteine, as a model system. The half-maximum inhibitory activities (IC 50) of the enzymes were determined as parameters of rectangular hyperbolas and correlated with the stability constant (K s) of the respectivemetal- ion-L-cysteine complex. The linear Dixon plots indicate equilibrium binding of the investigated ions to both enzymes.

Effect of transition metal (Cr, Mn, Fe, Co, Ni and Cu) on the hydrogenation properties of chloronitrobenzene over Pt/TiO2 catalysts

Selective hydrogenation of chloronitrobenzene to the corresponding chloroaniline has been studied in ethanol at 303 K and normal pressure over Pt/TiO 2 catalyst modified by transition metal (Cr, Mn, Fe, Co, Ni and Cu). The influence of transition metal (Cr, Mn, Fe, Co, Ni and Cu) on the hydrogenation properties of chloronitrobenzene (CNB) over Pt/TiO 2 catalyst has been studied in ethanol at 303 K and normal pressure. The hydrogenation of CNB can be carried out over Pt/TiO 2 catalyst. The order of the hydrogenation rate of CNB is m > p > o , and the yield of chloroaniline (CAN) is p > m > o . The effect of transition metal may be interpreted by electronic effect. Electron deficient species of the second element promote the specific rate constant turnover frequency (TOF) expressed on a per surface Pt atom by activating the nitrogen–oxygen bond. The conversion of CNB is over 99% and chloroaniline is main product on the hydrogenation of CNB over PtM/TiO 2 catalysts. PtFe/TiO 2 catalyst shows the best selectivity of CNB to CAN, and 98.0 mol% for p -CAN, 98.5 mol% for m -CAN and 98.7 mol% for o -CAN, respectively. Both catalytic activity and yield of p -CAN increase with addition of Fe over Pt/TiO 2 on the hydrogenation of p -CNB.

Thermodynamic modeling of glass melt systems — applications for the glass industry

The influence of transition metal (Cr, Mn, Fe, Co, Ni and Cu) on the hydrogenation properties of chloronitrobenzene (CNB) over Pt/TiO2 catalyst has been studied in ethanol at 303 K and normal pressure. The hydrogenation of CNB can be carried out over Pt/TiO2 catalyst. The order of the hydrogenation rate of CNB is m>p>o, and the yield of chloroaniline (CAN) is p>m>o. The effect of transition metal may be interpreted by electronic effect. Electron deficient species of the second element promote the specific rate constant turnover frequency (TOF) expressed on a per surface Pt atom by activating the nitrogen–oxygen bond. The conversion of CNB is over 99% and chloroaniline is main product on the hydrogenation of CNB over PtM/TiO2 catalysts. PtFe/TiO2 catalyst shows the best selectivity of CNB to CAN, and 98.0 mol% for p-CAN, 98.5 mol% for m-CAN and 98.7 mol% for o-CAN, respectively. Both catalytic activity and yield of p-CAN increase with addition of Fe over Pt/TiO2 on the hydrogenation of p-CNB.

Investigation of magnetic properties and thermal stability of Fe-TM-B metallic glasses

The influence of transition metal (TM) additives on the Curie temperature ( T c), saturation magnetization ( M s) and thermal stability of binary Fe-B metallic glasses was investigated. Parallel changes were found in M s and T c, showing typical group number effects. Nearly linear correlation has been observed between the initial temperature and activation energy of crystallization.