Ni Doping Concentration Research Articles

Bound magnetic polaron driven room-temperature ferromagnetism in Ni doped ZnS nanoparticles

Magnetism in dilute magnetic semiconductors (DMSs) has been a controversial topic since its discovery. There are many models which predict the origin of room temperature ferromagnetism (RTFM) in TM doped wide band gap semiconductors. Here, we report RTFM in chemically synthesized cubic Zn1-xNixS (0 ≤ x ≤ 0.08) DMS nanoparticles of ∼3–5 nm size. Ferromagnetic behavior (at 300 K and 5 K) was found to increase with the increase in Ni doping concentration and was understood due to defect induced ferromagnetism. The low temperature magnetization measurement (ZFC-FC) shows that the nanoparticles are strongly coupled by magnetic interactions. Optical studies showed decrease in the energy bandgap along with the presence of sulfur and zinc vacancies and surface defects. Low temperature resistivity measurement depicted the semiconducting nature of the synthesized samples. With increase in doping concentration, an increase in the resistive behavior was observed which was explained in the realm of defects states created due to doping of the Ni ions.

Energy Storage in a Transition Metal Doped MOF Derived Carbon Nanostructure

We illustrate a novel concept in tailoring the architecture of MOF-derived carbons by doping MOF crystals with transition metal ions prior to carbon structure growth via chemical vapor deposition (CVD). MOF-5 was isomorphously doped with various concentrations of Ni2+ during synthesis and was subsequently subjected to CVD to grow a labyrinth of carbon nanofibers (CNF) with high electrical conductivity and higher surface area than that of the parent MOF. TEM of the inner structure of the CNFs revealed a chevron arrangement with ~0.34 nm visible fringe spacing. The CNF diameters increased with increasing Ni concentration. This is attributed to the decreasing distance between Ni dopants with increasing Ni concentration, which may facilitate coalescence of the Ni catalyst during the heat treatment and thereby increase the diameter of the resultant CNF. However, Ni doping concentration greater than 30% led to large agglomerations of Ni particles which eventually ceased CNF growth. The electrical conductivity and the electrochemical double layer capacitance of the CNFs also increased with increasing Ni concentrations. The highest electrochemical double layer capacitance and the lowest resistance was observed at a Ni doping concentration of 30%. An alkaline electrolyte was used to engage the Ni particles inside the CNFs to participate in a reversible redox reaction shuttling between Ni and Ni(OH)2, which resulted in a specific capacitance as high as 349 F/g. The possibility of doping transition metals into a wide variety of MOF structures can provide a new method to synthesize novel carbon structures with high energy storage capabilities.

Tailoring of optical band gap and electrical conductivity in a-axis oriented Ni doped Chromium Oxide thin films

Ni doped Cr2O3 (NCO) films have attracted much attention due to their applications in the field of photovoltaics. This study reports the tailoring of structural, electrical and optical properties as a function of Ni doping in Chromium oxide (Cr2O3). NCO thin films were grown by Pulsed laser deposition (PLD) using 2nd harmonic Nd:YAG Laser on n-Si (100) with in-situ annealing of 450 °C. Structural analyses based on X-ray diffractometry (XRD) and Raman Spectroscopy showed the inconsistent variation in crystallinity and shift in A1g band in turn revealing the successful incorporation of Ni into Chromium oxide host lattice. In addition, electrical measurements also showed an inconsistent variation in resistivity ranging from 102 to 104Ω−cm. The properties showed widening of band gap energy (Eg) from 3.41 to 3.60 eV as a function of Ni doping concentration with significantly decreased reflectance in the range of 500–600 nm thereby increasing the absorption, a pre-requisite for solar absorbers.

Characteristics of the Li-Ni Doped Cobalt Oxide Thin Films Prepared by Pulsed Laser Deposition.

Cobalt oxide spinel thin films doped with Ni and Li were deposited on c-sapphire single crystal substrates at various substrate temperatures and oxygen partial pressures by pulsed laser deposition. The effects of the doping and processing parameters on the crystal structure, electrical and optical properties of cobalt oxide base spinel thin films were analyzed by XRD, four point probe and UV spectrometry. The electrical conductivity increased with increasing Ni doping concentration, x, up to x = 0.7. The thin films grew on the sapphire substrates with a strong (111) preferred orientation. Li0.1Ni0.6Co2.3O4 spinel phase decomposed to a rock salt phase when the oxygen partial pressure was lower than 5 mtorr. The electrical conductivity decreased rapidly with the formation of a rock salt phase due to the limited charge transfer between the divalent and trivalent cations.

Magnetic field effect on the electrical resistivity of Y1−xNixBa2Cu3O7−δ superconductor

The Ni- substituted Y1−xNixBa2Cu3O7−δ high temperature superconducting samples with 0 ≤ x < 0.01 were synthesized by the standard solid-state reaction. The temperature dependent resistivity of the samples was measured under magnetic fields in the range of zero to 1 Tesla, applied perpendicular to the current direction. To study of magnetoresistance is one of the most important ways to investigate the intergranular nature of superconducting materials. The resistive transition is made of two parts. The first- unaffected to applied magnetic field part which is near the onset of superconductivity. This region is due to superconductivity in grains. The second- broaden tail part which is due to the connectivity of the grains. At temperatures close to Tc 0, (ρ = 0), under applied magnetic fields, weak links are affected and the vortices are penetrated and move inside the intergranular and then the tail part is broaden. This broadening part observed in the electrical resistivity, ρ(T), and in the derivative of the electrical resistivity, dρ/dT, becomes too small or even absent in Ni doped samples. For pure sample, Tc 0 was around 90 K; by applying a magnetic field H = 0.3 T it shifted to 40 K. This broadening is 91.4 K to 80 K for x = 0.002 and 91.7 K to 85 K for x = 0.004 samples. We found an optimal value of Ni doping concentration which improves the coupling of the grains. Then, vortices get strongly pinned. These observations suggest that the Ni substitution can reduce the weak links and increase the Jc values of these superconductors.

Ni-doped TiO2 nanotubes supported Ru catalysts for CO selective methanation in H2-rich reformate gases

In this study, Ni-doped TiO2 nanotubes (Ni-TNTs) with increased thermal stability and improved tubular morphology were successfully prepared via a facile hydrothermal method. Detailed characterization results showed that the Ni element was successfully doped into TNTs structures, thereby resulting in increased thermal stability of TNTs, as reflected by the morphology changing from nanoparticles to nanorods and finally to nanotubes with the increase of Ni doping content. After impregnation of Ru, the resultant Ru/Ni-TNTs catalysts showed excellent catalytic performance for CO selective methanation in H2-rich reformate gases for fuel cell applications, which can deep-remove the CO outlet concentration to below 10 ppm at a selectivity greater than 50% over a wide temperature range of 210–285 °C. The reason for the excellent performance of Ru/Ni-TNTs catalyst is mainly due to the increased specific surface area and thermal stability of Ni-TNTs support, the improved dispersion of supported Ru nanoparticles, and the enhanced chemisorption capability for CO.

Synthesis and Thermoelectric Properties of Ni-Doped ZrCoSb Half-Heusler Compounds

The Ni-doped ZrCo1−xNixSb half-Heusler compounds were prepared by arc-melting and spark plasma sintering technology. X-ray diffraction analysis results showed that all samples were crystallized in a half-Heusler phase. Thermoelectric properties of ZrCo1−xNixSb compounds were measured from room temperature to 850 K. The electrical conductivity and the absolute value of Seebeck coefficient increased with the Ni-doping content increasing due to the Ni substitution at Co. sites. The lattice thermal conductivity of ZrCo1−xNixSb samples was depressed dramatically because of the acoustic phonon scattering and point defect scattering. The figure of merit of ZrCo1−xNixSb compounds was improved due to the decreased thermal conductivity and improved power factor. The maximum ZT value of 0.24 was achieved for ZrCo0.92Ni0.08Sb sample at 850 K.

H2S sensing characteristics of Ni-doped CaCu3Ti4O12 films synthesized by a sol-gel method

The problem of detecting the toxic hydrogen sulfide (H2S) gas at part per million levels in air by means of simple solid state gas sensors is relevant to environmental and gas processing industries. In this work, high-performance H2S gas sensors are developed based on nickel-doped calcium copper titanate (Ni-doped CCTO) thin films synthesized by a sol-gel method. From gas-sensing measurements, the response of Ni-doped CCTO sensing films increased substantially with increasing Ni doping level from 1.5 to 7.3 wt%, revealing a catalytic effect of Ni on the surface reactions with adsorbed H2S molecules. In particular, 7.3 wt% Ni-doped CCTO sensors offered a high response of 120 for 10 ppm of H2S at the optimal operating temperature of 250 °C, an order of magnitude higher than that of undoped one. In addition, the response time dropped significantly from ∼80 s to ∼4 s while the recovery time slightly improved as the Ni doping content increased from 0 to 7.3 wt%. Moreover, the Ni-doped CCTO sensors exhibited good reproducibility and high H2S selectivity against ethanol, H2, NO2 and NH3. Therefore, the Ni-doped CCTO sensors are highly promising for sensitive and selective detections of H2S.

Local structure investigation of Ni doped ZnO thin films by X-ray absorption spectroscopy

Radio Frequency magnetron sputtering technique has been used to prepare Ni doped ZnO thin films with varying Ni doping concentration of upto 10at.%. Grazing Incidence X-ray Diffraction results show wurtzite structure of the samples throughout the Ni concentration range while X-ray Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure results at Zn and Ni K edges show that Ni is substituting Zn in ZnO lattice and no other extra phase is present in the samples. The substitution of Zn by Ni is further confirmed by O K-edge XANES measurements. Photoluminescence measurements on the samples and theoretical simulations of the XANES spectra at Ni and O K-edges have been used to explain the room temperature ferromagnetic character on the basis of the presence of oxygen vacancies in the samples.

Transition of Magnetic Characteristics from Paramagnetic State to Ferromagnetic Phase in Ce1−xNixO2 Nanoparticles

Nowadays, oxide-based diluted magnetic semiconductor nanoparticles are the most reliable compounds, wherein they accommodate both spin as well as charge of the electron in single domain, means most preferable for the fabrication of spintronic devices. In this view, we report on new Ce1−xNixO2 (x = 0.00, 0.02, 0.04, 0.06, and 0.08) nanoparticles prepared by precipitation method via polyethylene glycol as a surfactant. XRD analysis revealed that all the synthesized nanoparticles were crystallized in distinct FCC fluorite structure as that of CeO2 host lattice. Transmission electron microscopy analysis confirmed that all the synthesized samples were in spherical shape with average particle size of 8–10 nm, which is well concord with the grain size estimated from the Scherrer formula. The vibrating sample magnetometer evaluations suggested that pristine host lattice shows signals of paramagnetism; meanwhile, Ni substitution CeO2 nanoparticles exhibits strong ferromagnetism at room temperature. Particularly, 4% Ni-doped CeO2 samples shows enhanced ferromagnetism and which is suppressed with raising dopant concentration. The perceived magnetization with respect to the Ni dopant concentration is well anticipated by F-center exchange mechanism. We expect that the observations in this research suggest suitable path for preparing of various oxide-based diluted magnetic semiconductor nanoparticles and their applications in fabrication of spintronic devices.

First principles study of the magnetic properties and charge transfer of Ni-doped BiFeO3

We present a first-principles study of electronic structures and magnetic properties in Ni-doped BiFeO3 using the density functional theory+U methods. The BiNixFe1-xO3 (x=0.125, 0.25, 0.5) multiferroic ceramics represent ferromagnetic properties due to the ferrimagnetic order in Ni-O-Fe, and the magnetic moment rises with increase in Ni doping concentration agreeing well with experimental results. Ni atoms prefer to occupy the diagonal positions in the quasi-plane Ni-O-Fe eight-membered ring. Charge transfer from Bi 6s state to Ni 3d state through O 2p orbital lead to the 2+ oxidation state of Ni, indicating high Néel temperatures of BiNixFe1-xO3, and the electronic state of the system can be described as Bi4+xBi3+1-xNi2+xFe3+1-xO3. The spin polarization of Bi 6s state and O 2p state near the Fermi level contributes to the total magnetic moment. A spin-polarized acceptor level of about 0.4eV constituted by Bi 6s state and O 2p state is found, which is responsible for the increase in leakage current of Ni-doped BiFeO3.

Photoelectrochemical properties of Ni-doped CuO nanorods grown using the modified chemical bath deposition method

Ni-doped CuO nanorods were grown on a CuO film buffered with a FTO substrate using different nickel amounts via the modified chemical bath deposition method. We investigated the effect of the Ni doping concentration on the morphological, optical, structural and photoelectrochemical properties of the Ni-doped CuO nanorods. In this study, the maximum photocurrent density of −1.75mA/cm2 at −0.55V (vs. SCE) was obtained from the Ni-doped CuO photoelectrode with a Ni doping concentration of 1at.% and an effective route to improve the photocurrent density of the CuO photoelectrode was proposed.

Synthesis and electrochemical performance of Ni doped Na3V2(PO4)3/C cathode materials for sodium ion batteries

To improve the electrochemical performances of Na3V2(PO4) cathode materials in sodium ion batteries, Na3V2-xNix(PO4)3/C (x = 0, 0.01, 0.03 and 0.05) materials were designed and prepared through a facile sol-gel route. The effect of Ni doping on the composition and crystal structure of Ni doped Na3V2(PO4)/C samples was investigated. The results confirmed that Ni atoms were successfully doped into Na3V2(PO4) crystal and substituted the V sites. It is shown that a carbon layer of about 2 nm was covered on the particle surface of the sample, which is beneficial for enhancing the electronic conductivity. The discharge capacities of all Ni doped samples were improved at high rates (2, 5 and 10 C). When Ni doping content was 3%, the sample exhibited the best rate performance and cycling capability. Na3V1.97Ni0.03(PO4)3/C sample delivered the specific capacity of 98.1 mAh·g−1 at 5 C, which is much higher than that of pristine sample, 64.3 mAh·g−1. The capacity retentions of Na3V1.97Ni0.03(PO4)3/C and pristine samples were 93.5% and 60.2%, after 50 cycles at 5 C, respectively. Electrochemical impedance spectroscopy and cyclic voltammetry performance analyses revealed that the polarization of the electrodes decreased and the diffusion coefficient of sodium ions increased by Ni doping.

Chemical synthesis, structural, optical, magnetic characteristics and enhanced visible light active photocatalysis of Ni doped CuS nanoparticles

In this paper, we report systematic investigations on the effects of Ni doping on the structural, optical, magnetic and photocatalytic characteristics of CuS nanoparticles synthesized by simplistic wet chemical co-precipitation route via EDTA molecules as templates. XRD studies confirmed that accurate phase formation of synthesized nanoparticles and chemical composition were obtained by EDX. Magnetic measurements revealed that 3% Ni doped CuS nanoparticles show signs of good ferromagnetism at room temperature and transition of magnetic signs from ferromagnetic to paramagnetic nature by increasing the Ni dopant concentration in CuS host matrix. The photocatalytic degradation efficiency of the prepared pure and Ni doped CuS nanoparticles were evaluated as a function of simulated sunlight irradiation via RhB organic dye pollutant as a test molecule. Particularly, in the presence of 3% Ni doped CuS nanoparticles in pollutant solution 98.46% degradation efficiency was achieved within 60 min of sunlight irradiation; meanwhile bare CuS attained only 83.22%. Further, after five cycles 3% Ni doping CuS nanoparticles exhibit good photocatalytic stability with very negligible catalyst loss. We believe that the investigations in this study provides adaptable pathway for the synthesizing of various diluted magnetic semiconductor nanoparticles and their applications in spintronic devices as well as sunlight-driven photocatalysts intended for wastewater purification.

Optical and Magnetic Properties of Ni Doped ZnS Diluted Magnetic Semiconductors Synthesized by Hydrothermal Method

Diluted magnetic semiconductors Zn1-xNixS with different consistency ratio (x = 0, 0.01, 0.03, 0.05, and 0.07) were successfully synthesized by hydrothermal method using ethylenediamine as a modifier. The influence of Ni doping concentration on the microstructure, morphology, and optical and magnetic properties of undoped and Ni doped ZnS nanocrystals was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectrometry (XEDS), ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), photoluminescence spectra (PL), and the vibrating sample magnetometer (VSM), respectively. The experiment results show the substitution of Ni2+ on Zn2+ sites without changing the hexagonal wurtzite structure of ZnS and generate single-phase Zn1-xNixS with good crystallization. The lattice constant causes distortion and decreases with the increase of Ni2+ doped concentration. The appearance of the samples is one-dimensional well-dispersed nanorods. UV-vis spectra reveal the band gap of all Zn1-xNixS samples greater than that of bulk ZnS (3.67 eV), and blue shift phenomenon occurs. The photoluminescence spectra of undoped and doped samples possess the broad blue emission band in the range of 400–650 nm; the PL intensities of Zn1-xNixS nanorods increase with the increase of Ni content comparing to pure ZnS and reach maximum for x = 0.03. Magnetic measurements indicated that the undoped ZnS samples are superparamagnetic, whereas the doped samples exhibit ferromagnetism.

Spin-coated nickel doped cadmium sulfide thin films for third harmonic generation applications

In the current study, different percentages of Nickel (0%, 2%, 4% and 6%) doped CdS thin films have been deposited on glass substrates by the sol-gel spin-coating technique. Before performing the nonlinear optical studies, the structural, morphological and optical properties were examined as a function of Ni doping concentration through the XRD, SEM, AFM and UV–vis spectrometry, respectively. According to the XRD patterns, all films are polycrystalline and the incorporation of Ni does not change qualitatively the crystalline phase of CdS. The Ni doping affects the surface morphology of the CdS thin films which is indicated by scanning electron microscopy and atomic force microscopy images. The band gap was determined via the equation related to the absorption coefficient. It's deduced that the optical band-gap values increased from 2.35 eV to 2.41 eV depending on Ni content. Though, the nonlinear optical properties were determined based on the measurements of the third harmonic generation (THG) using the rotational Maker fringe technique. The results showed that the third order nonlinear optical susceptibilities oscillate between 5.40 × 10−21 m2/V2 for CdS:Ni (2%) and 4.98 × 10−21 m2/V2 for CdS:Ni (6%) while the pure CdS one falls inward, with a value of 5.09 × 10−21 m2/V2.

In situ Ni-doping during cathodic electrodeposition of hematite for excellent photoelectrochemical performance of nanostructured nickel oxide-hematite p-n junction photoanode

Nanostructured nickel oxide-hematite (NiO/α-Fe2O3) p-n junction photoanodes synthesized from in situ doping of nickel (Ni) during cathodic electrodeposition of hematite were successfully demonstrated. A postulation model was proposed to explain the fundamental mechanism of Ni2+ ions involved, and the eventual formation of NiO on the subsurface region of hematite that enhanced the potential photoelectrochemical water oxidation process. Through this study, it was found that the measured photocurrent densities of the Ni-doped hematite photoanodes were highly dependent on the concentrations of Ni dopant used. The optimum Ni dopant at 25M% demonstrated an excellent photoelectrochemical performance of 7-folds enhancement as compared to bare hematite photoanode. This was attributed to the increased electron donor density through the p-n junction and thus lowering the energetic barrier for water oxidation activity at the optimum Ni dopant concentration. Concurrently, the in situ Ni-doping of hematite has also lowered the photogenerated charge carrier transfer resistance as measured using the electrochemical impedance spectroscopy. It is expected that the fundamental understanding gained through this study is helpful for the rational design and construction of highly efficient photoanodes for application in photoelectrochemical process.

The effect of Ni doping concentration on the gas sensing properties of Ni doped SnO2

The Ni doped SnO2 has been prepared by two-step hydrothermal treatment and calcination, and characterized by XRD, TEM and Brunauer Emmett Teller N2 adsorption–desorption analysis. The results exhibit the Ni doped SnO2 is heterostructure composed of Ni-SnO2 on the surface of SnO2 nanoparticles, which are polycrystalline tetragonal with high specific surface area and average grain size of about 10nm. The sensors based on Ni doped SnO2 show very good gas sensing properties at low working temperature. The gas sensing properties of the Ni doped SnO2 are improved with low Ni-doping concentration (2–4mol%), but further increase of Ni-doping concentration results in deteriorated response by low conductivity. The sensor based on 2mol% Ni doped SnO2 and the sensor based on 4mol% Ni doped SnO2 show ultrahigh responses to n-butanol and formaldehyde, respectively, with good selectivity. These sensors could be promising candidates for selective detection of n-butanol and formaldehyde.

Structural and room temperature ferromagnetic properties of Ni doped ZnO nanoparticles via low-temperature hydrothermal method

A series of Zn1−xNixO (x=0, 1%, 3%, 5%) nanoparticles have been synthesized via a low-temperature hydrothermal method. Influence of Ni doping concentration on the structure, morphology, optical properties and magnetism of the samples was investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV–vis spectrophotometer and vibrating sample magnetometer instruments. The results show that the undoped and doped ZnO nanoparticles are both hexagonal wurtzite structures. The surface analysis was performed using X-ray photoelectron spectroscopic studies. The images of SEM reveal that the structure of pure ZnO and Ni doped samples are nanoparticles which intended to form flakes with thickness of few nanometers, being overlain with each one to develop the network with some pores and voids. Based on the ultraviolet–visible (UV–vis) spectroscopy analysis, it indicates that the band gap energy decreases with the increasing concentration of Ni. Furthermore, The Ni doped ZnO samples didn't exhibit higher ultraviolet-light-driven photocatalytic activity compared to the undoped ZnO sample. Vibrating sample magnetometer was used for the magnetic property investigations, and the result indicates that room temperature ferromagnetism property of 3% Ni doped sample is attributed to oxygen vacancy and interaction between doped ions.

Tuning the physical properties of PbS thin films towards optoelectronic applications through Ni doping

Ni-doped PbS (PbS:Ni) thin films were deposited on glass substrates by cost-effective spray pyrolysis technique with different concentrations of Ni (0, 2, 4, 6 and 8 at.%). XRD studies reveal that all the films exhibit face centered cubic structure. The preferential orientation of the undoped PbS film is along the (2 0 0) plane and for the doped films the preferential orientation is along the (1 1 1) plane. Optical studies show that the film transparency increases with increase in Ni doping concentration and the optical band gap exhibit a red shift from 2.26eV to 2.06eV. Electrical studies show that all the as deposited PbS:Ni thin films have resistivity in the order of 10−1Ω-cm. Raman studies reveal that the peak at 161cm−1 might have been originated from the combination of longitudinal and transverse acoustic phonon modes in PbS crystals. Increased transparency and nominal resistivity values obtained make PbS:Ni thin films suitable for optoelectronic applications especially in solar cells.