First-principles study of the stability,electronic and mechanical properties of Cr2N and CrN with the variation of Ni doping concentration

First-principles approach was applied to investigate the stability, electronic and mechanical properties of Cr_2-xNi_xN (x = 0, 0.083, 0.167,0.250, 0.333) and Cr_1-xNi_xN (x = 0,0.125,0.25,0.375, 0.5). The calculated formation enthalpy and mechanical stability results show that Cr_2-xNi_xN and Cr_1-xNi_xN are all stable. The bulk, shear and Young's modulus results indicate that different variation trend is observed in Cr_2-xNi_xN and Cr_1-xNi_xN with the increase of x. Base on Pugh and Pettifor criteria, Cr₂N belongs to the brittle area and the ductility of Cr_2-xNi_xN increases with the increment of x, obtain the maximum results when x = 0.333. However, CrN, which belongs to the ductile area, alloying with Ni decreases its ductility and increases its brittleness, reach the maximum brittleness when x = 0.5. The charge density difference study reveals that the doped Ni atom affects the interaction between Cr and N in Cr_2-xNi_xN and Cr_1-xNi_xN differently. Furthermore, the stress-strain curve of Cr₂N, Cr_1.833Ni_0.167N, and Cr_1.667Ni_0.333N under shear and tensile deformation shows that the ultimate stress of Cr₂N is decreased and its ductility increased. Nevertheless, the stress-strain curve of CrN, Cr_0.75Ni_0.25N, and Cr_0.5Ni_0.5N under shear and tensile deformation indicates that the strength of CrN can be enhanced and its deformation process is significantly changed when x = 0.25.     

Preparation of multiferroic composites of BaTiO3–Ni0.5Zn0.5Fe2O4 ceramics

Magneto-electric coupling in ceramic composites formed by ferroelectric and ferromagnetic phases can be obtained via an adequate mechanical coupling between the individual piezoelectric and magnetostrictive phases (product property). In the present work, the possibility of forming diphase ferroelectric–ferromagnetic ceramics has been investigated. Composites of xBaTiO₃–(1 − x)Ni_0.5Zn_0.5Fe₂O₄ with x = 0.5, 0.6 and 0.7 were prepared according two different procedures: (i) by direct mixing powders of perovskite BaTiO₃ and Ni_0.5Zn_0.5Fe₂O₄ spinel prepared by solid state and (ii) by coprecipitating Fe^III–Ni^II–Zn^II nitric salts in a NaOH solution in which the BaTiO₃ powders were previously dispersed. Optimum processing parameters for good homogeneity, densification and for a reduction of the chemical reactions at the interfaces ferroelectric-ferrite were found. A temperature and composition-dependent magnetic order is present in all the composites, with a dilution effect of the magnetisation due to the presence of the non-ferromagnetic phase. A diffuse ferroelectric–paraelectric transition due to the BaTiO₃ phase was identified by the temperature-dependence of the permittivity and losses, showing that at room temperature the material preserves a ferroelectric order. The interfaces play important roles in the dielectric properties, causing space charge effects and Maxwell–Wagner relaxation, particularly at low frequencies and high temperatures. The combined ferroelectric and magnetic ordering will result in magneto-electric coupling in this material; further investigations are necessary.     

Thermoelectric properties of Al and Mn double substituted ZnO

The effects of Al and Mn single and double substitution on structure, composition, and thermoelectric properties of ZnO have been investigated in three series of compounds; Zn_1−xAl_xO, Zn_1−xMn_xO (x=0,0.02,0.04,0.06,0.08) and Zn_1−2xAl_xMn_xO (x=0,0.01,0.02,0.03,0.04) prepared by thermal decomposition method. While the lattice structure is not affected by the substitutions, properties of the material are. Al and Mn have opposite effects on electrical conductivity and Seebeck coefficient of ZnO. Al substitution leads to an increase in electrical conductivity while Mn substitution increases absolute value of Seebeck coefficient. Double substituted samples seem to exhibit the effects from both ions though the increase in absolute value of Seebeck coefficient is less significant comparing to that observed in Mn single substituted samples. Nevertheless, the change in electrical conductivity is more pronounced and dominant in the power factor calculation. Thus the most conductive sample in this work, Zn_0.98Al_0.02O, shows the highest power factor of 1.03×10⁻⁴ WK⁻² m⁻¹at 800 K. The best double substituted sample is Zn_0.98Mn_0.01Al_0.01O which gives a power factor of 4.79×10⁻⁵ WK⁻² m⁻¹ at the same temperature.     

Synthesis and analysis of structural,compositional, morphological,magnetic, electrical and surface charge properties of Zn-doped nickel ferrite nanoparticles

Zn-doped nickel ferrite nanoparticles (Zn_xNi_(1-x)Fe₂O₄) were synthesized using the co-precipitation technique. The structural and compositional studies of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles revealed their face-centred cubic spinel structure and an appropriate amount of Zn doping in nickel ferrite nanoparticles, respectively. The morphological analysis had been carried out to obtain the particle size of the synthesized nanoparticles. The magnetic studies revealed the superparamagnetic nature of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles, and the maximum magnetization of 30 emu/g for the Zn_0.2N_0.8Fe₂O₄ sample. The M ? H curves were fitted with the Langevin function to obtain the magnetic particle diameter of Zn_xNi_(1-x)Fe₂O₄ nanoparticles. The electrical conduction in Zn_xNi_(1-x)Fe₂O₄ nanoparticles was explained through the Verway hopping mechanism. The Zn_0.2N_0.8Fe₂O₄ nanoparticle exhibited a higher electrical conductivity of 42 μS/cm and surface charge of ?29/7 mV due to the enhanced hopping of Fe³⁺ ions in the octahedral sites. Owing to this nature, they were identified as the suitable candidates in the applications such as thermoelectrics, hyperthermia, magnetic coating and for the preparation of conducting ferrofluids.     

Influence of post-annealing atmosphere on microstructure,optical and electrical properties of zinc cadmium oxide films deposited by DC and RF magnetron co-sputtering

Zinc cadmium oxide (Zn_1−xCd_xO) films were deposited on quartz substrates by direct current (DC) and radio frequency (RF) reactive magnetron co-sputtering and the influence of post-annealing atmosphere on their microstructure, optical and electrical properties were investigated by X-ray diffraction (XRD), optical absorbance, photoluminescence (PL) and Hall measurements. Results indicate that the band gap (E_g) of all Zn_1−xCd_xO films annealed in different atmospheres are smaller than that of the undoped ZnO, the observed shifts in E_g being 0.43, 0.37 and 0.32 eV for the Zn_1−xCd_xO films annealed in argon, oxygen and vacuum, respectively. Hall measurement results indicate that all Zn_1−xCd_xO films annealed in different atmospheres show the n-type conduction, but the Zn_1−xCd_xO film annealed in vacuum has low resistivity and high concentration, which has room-temperature resistivity of 1.59 Ω cm and carrier concentration of 2.07×10¹⁷ cm⁻³. Compared with Zn_1−xCd_xO films annealed in oxygen and argon, Zn_1−xCd_xO film annealed in vacuum has the best crystal quality, luminescence and electrical properties. The influencing mechanism of the post-annealing atmosphere on the electrical and optical properties of the Zn_1−xCd_xO film is discussed.     

Multiple magnetic phase transitions in NixMn1-xCo2O4

We prepared pure-phase Ni_xMn_1-xCo₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles using a low-temperature solid-state reaction method. Magnetization measurement results showed that with Ni doping, the Curie temperature and coercivity of Ni_xMn_1-xCo₂O₄ increased. Multiple magnetic phases that transition from paramagnetic to ferrimagnetic to ferrimagnetic and antiferromagnetic were observed to coexist in the Ni_0.5Mn_0.5Co₂O₄ sample. At low temperatures, the ferromagnetic and antiferromagnetic phases coexist in Ni_xMn_1-xCo₂O₄ (x = 0 and 0.25), and as the concentration of Ni increases, Ni_xMn_1-xCo₂O₄ (x = 0.75 and 1) show a spin glass state. The structure of Ni_xMn_1-xCo₂O₄ (x < 0.5) is mainly affected by cation defects, and by cation substitution when x is greater than 0.5. The results of first-principles calculations show that covalent bonds exist in Ni_xMn_1-xCo₂O₄ and that the strength of the Ni-O bond is greater than that of the Mn-O bond.     

Extremely high corrosion resistance of ZnxNi1–xCr2O4 spinel as sidewalls in the aluminum electrolyte

The sidewall material is a key component in new electrolytic cell with an inert electrode for the aluminum electrolysis industry. The continuous development of novel sidewall materials with excellent corrosion resistance in molten salts electrolyte is an important topic. Herein, a new system of sidewall material, spinel structured Zn_xNi_1–xCr₂O₄ (x = 0 – 1), is prepared by solid-phase reaction and the corrosion-resistance enhancement is investigated. The results prove that Zn²⁺ plays two roles in the Zn_xNi_1–xCr₂O₄ spinels. Firstly, Zn²⁺ tunes the surface energies of spinels resulting in the octahedral grains, which suppresses the cation diffusion in the corrosion process. Secondly, Zn²⁺ stabilizes the Cr³⁺ in the spinels. As a result, the Zn_0.5Ni_0.5Cr₂O₄ spinel displays an extremely low corrosion rate ～0.007 cm·a^–1 in NaF-KF-AlF₃ bath at 800 °C comparing with other sidewall materials. The as-obtained spinel shows great potential as a novel sidewall material for the new electrolytic cell.     

Boosting the electrocatalytic activity of lanthanum cobaltite ceramic through Zn doping for the oxygen evolution reaction

The development of economical and highly efficient electrocatalysts is crucial for the oxygen evolution reaction in water electrolysis, which is associated with producing clean and sustainable hydrogen fuel. For this purpose, we successfully elaborated a new series of LaCo_1-xZn_xO₃ oxides (x = 0, 0.1, 0.2, 0.3 and 0.4) via a facile sol-gel route and investigated their structural, morphological and electrochemical properties for a possible use as electrocatalysts toward oxygen evolution reaction in a basic solution. Among the developed materials, the LaCo_0.9Zn_0.1O₃ electrocatalyst displays a remarkable performance; an overpotential of merely 327 mV is needed to generate a specified current density of 10 mA.cm⁻²_geo; a current density of around 73.41 mA cm⁻² at 450 mV, almost twice as high compared to the pristine electrocatalyst; a faster reaction kinetic with a lower Tafel slope of ∼92 mV.dec⁻¹ and an activity loss of less than 4% after 24 h of utilization.     

High-temperature thermoelectric properties of polycrystalline Zn1−x−yAlxTiyO ceramics

The as-sintered Zn_1−xAl_xO (0 ≤ x ≤ 0.05) samples crystallized in the ZnO with a wurtzite structure, along with a small amount of the cubic spinel ZnAl₂O₄. The addition of Al₂O₃ to ZnO gave rise to a decrease in grain size, ranging from 7.3 to 2.7 μm and in relative density, ranging from 99.2 to 90.1% of the theoretical density. In the Zn_0.97Al_0.03−yTi_yO samples, as the amount of TiO₂ increased, the grain size of ZnO grains and second phases, such as Zn₂TiO₄ and ZnAl₂O₄, as well as density increased. The co-doping of Al and Ti led to a significant increase in both the electrical conductivity and the absolute value of the Seebeck coefficient, resulting in an increase in the power factor. The highest value of power factor (3.8 × 10⁻⁴ W m⁻¹ K⁻²) was attained for Zn_0.97Al_0.02Ti_0.01O at 800 °C. It is demonstrated that the Al and Ti co-doping is fairly effective for enhancing thermoelectric properties.     

Negative thermal expansion coefficient of Sc-doped indium tungstate ceramics synthesized by co-precipitation

Co-precipitation was successfully applied to synthesize the Sc³⁺ doped In_2-xSc_x (WO₄)₃ (x = 0, 0.3, 0.6, 0.9 and 1.2) compounds. The composition- and temperature-induced structural phase transition and thermal expansion behaviors of Sc³⁺ doped In₂(WO₄)₃ were investigated. Results indicate that In_2-xSc_x (WO₄)₃ crystalizes in a monoclinic structure at 300 °C for x ≤ 0.3 and changes into hexagonal structure for x ≥ 0.6. Hexagonal In_1.1Sc_0.9(WO₄)₃ displays negative thermal expansion (NTE) with an average linear coefficient of thermal expansion (CTE) of −1.85 × 10⁻⁶ °C ⁻¹. After sintering at 700 °C and above, a phase transition from hexagonal to orthorhombic phase was observed in In_2-xSc_x (WO₄)₃ (x ≥ 0.6). Sc³⁺ doping successfully reduce the temperature-induced phase transition temperature of In_2-xSc_x (WO₄)₃ ceramics from 250 °C (x = 0) to room temperature (x = 0.9). When x = 0.9 and 1.2, the average linear CTEs of In_2-xSc_x (WO₄)₃ ceramics are −5.45 × 10⁻⁶ °C⁻¹ and -4.43 × 10⁻⁶ °C⁻¹ in a wider temperature range of 25–700 °C, respectively.     

Role of Mn doping on magnetic properties of multiferroic NiCr2O4 nanoparticles

The structural and magnetic properties of Mn doped Nickel Chromite (Ni_1-xMn_xCr₂O_4, x = 0, 0.2, 0.3, 0.4, 0.6, 0.8) nanoparticles (NPs) were studied in detail. The X-ray diffraction analysis affirms normal spinel structure for all the samples and average crystallite size was found in the range 31–58 nm. The spinel structure of these nanoparticles was also confirmed by Fourier transform infrared spectroscopy which revealed the formation of tetrahedral and octahedral vibrational bands in the range 607 -628 cm^?1 and 486 - 491 cm^?1, respectively. Transmission electron microscopy images depicts less agglomerated and non-spherical shaped NPs. The temperature dependent zero field cooled and field cooled magnetic measurements revealed a paramagnetic to ferrimagnetic transition T_c at 87 K for NiCr₂O₄ NPs, which is shifted to low temperatures by Mn doping. This effect was attributed to cationic distributions between adjacent sites produced by Mn doping. M ? H loops of Ni_1-xMn_xCr₂O₄ NPs revealed enhanced saturation magnetization with increase in Mn doping which is attributed to a large magnetic moment of Mn ions. Ni_1-xMn_xCr₂O₄ (x = 0.6 and 0.8) NPs show steps in their M ? H loops because of exchange interactions between two sites of these NPs.     

Nb5+ ion substitution assisted the magnetic and gyromagnetic properties of NiCuZn ferrite for high frequency LTCC devices

Nowadays, developing nickle zinc ferrites with excellent magnetic and gyromagnetic properties are of great importance for solving the matching problem of 5G communication system. However, much is discussed about soft magnetic properties, but little is reported gyromagnetic properties that is critical for microwave device applications. Herein, Nb⁵⁺ ions substituted Ni_0.29Cu_0.18Zn_0.53Nb_xFe_2-xO₄ (x = 0.00-0.05), possessing high saturation magnetization, approriate initial permeability, high cut-off frequency and low ferromagnetic resonance linewidth (@9.55 GHz), were synthesized by low-temperature firing (900 °C). The phase structure and morphology evolutions were studied in detail. The results of morphology observations revealed that Nb⁵⁺ substitution has significant role in determining produce compact and uniform microstructures of NiCuZn ferrites via suppress the grain growth, which further corresponding enhance the magnetic and gyromagnetic properties. As a result, a uniform and compact grain size can be obtained, corresponding to the change of magnetic and gyromagenetic properties have different trends. Enhanced magnetic and gyromagnetic performance including high initial permeability (μ' = 203 @1 MHz), saturation magnetization (4πM_s = 3966 Gauss) and low ferromagnetic resonance linewidth (ΔH = 203 Oe) of the NiCuZn ferrites is achieved though adjusting Nb⁵⁺ ions substitution. More importantly, this work not only for low temperature co-fired ceramic (LTCC) technology but also for high frequency and microwave frequency devices including phase shifter and radars.     

Zinc substitution effect on the structural,spectroscopic and electrical properties of nanocrystalline MnFe2O4 spinel ferrite

This paper reports the structural, morphological, spectroscopic, dielectric, ac conductivity, and impedance properties of nanocrystalline Mn_1-xZn_xFe₂O₄. The nanocrystalline Mn–Zn ferrites were synthesized using a solvent-free combustion reaction method. The structural analysis using X-ray diffraction (XRD) pattern reveals the single-phase of all the samples and the Rietveld refined XRD patterns confirmed the cubic-spinel structure. The calculated crystallite size values increase from 8.5 nm to 19.6 nm with the Zn concentration. The surface morphological analysis using field emission scanning electron microscopy and the transmission electron microscopy confirms the nano size of the prepared ferrites. X-ray photoelectron spectroscopy was used to study the ionic state of the atoms present in the samples. Further, the high-resolution Mn 2p, Zn 2p, Fe 2p, and O 1s spectra of Mn_1-xZn_xFe₂O₄ does not result in the appearance of new peaks with Zn content, indicating that the Zn substitution does not change the ionic state of Mn, Zn, Fe, and O present in nanocrystalline Mn_1-xZn_xFe₂O₄. The investigated electrical properties show that the dielectric constant, tan δ and ac conductivity gradually decrease with increasing Zn substitution and the sample Mn_0·2Zn_0·8Fe₂O₄ has the lowest value of conductivity at 303 K. The ac conductivity measured at different temperatures shows the semiconducting nature of the ferrites. The impedance spectra analysis shows that the contribution of grain boundary is higher compared with the grain to the resistance. The obtained results suggest that the Zn substituted manganese ferrite nanoparticles can act as a promising candidate for high-frequency electronic devices applications.     

Effect of indium substitution on the structure and magnetic characteristics of ternary iron-based nitrides

In this paper, the structure and magnetic behaviour of antiperovskite In_xFe_4-xN have been investigated systematically. The crystal lattice becomes larger and the Curie temperature decreases with increasing x. The magnetic state changes from a ferromagnetic to a glassy state. In addition, an obvious spin glass (SG) behaviour has been revealed in In_0.6Fe_3.4N (x = 0.6) with a freezing temperature of T₀ = 73 K, dynamical exponent of zν = 5.51, and flipping time of τ₀ = 4.26 × 10⁻¹¹ s. The origin of the SG behaviour in In_0.6Fe_3.4N may be attributed to atomic disorders at Wyckoff position 1a or ferromagnetic frustrations, or the both.     

A unique method to fabricate NixMg1 − xO (111) nano-platelet solid solution catalyst for CH4-CO2 dry reforming

A facile solvothermal route is established to generate Ni_xMg_1 − x(OH)(OCH₃) platelet covered by (001) facets. Thermolytic decomposition of Ni_xMg_1 − x(OH)(OCH₃) is topotactic and leads to the formation of Ni_xMg_1 − xO solid solution enclosed by reactive Tasker III type (111) facets. Both Mg and Ni are found to be distributed evenly in the solid solution. The reduced Ni_xMg_1 − xO platelet is a stable catalyst in CH₄-CO₂ dry reforming for a 100 h test.     

Extended X-ray absorption fine structure,X-ray diffraction and Raman analysis of nickel-doped Ba(Mg1/3Ta2/3)O3

Raman, X-ray diffraction and extended X-ray absorption fine structure (EXAFS) measurements of xBa(Ni_1/3Ta_2/3)O₃ + (1 − x)Ba(Mg_1/3Ta_2/3)O₃ samples with x = 0–0.03 were performed to reveal the nickel doping effect on the microwave properties. EXAFS result clearly shows that the nickel is located on the Mg lattice site. We also found that, as the nickel concentration increases, microwave dielectric constant decreases with the TaO and NiO bond distances. X-ray diffraction shows that the 1:2 ordered structure is degraded with the increasing of nickel concentration. The stretching phonon of the TaO₆ octahedra, that is A_1g(O) phonon near 800 cm⁻¹, are strongly correlated to the microwave properties of xBa(Ni_1/3Mg_2/3)O₃ + (1 − x)Ba(Mg_1/3Ta_2/3)O₃ samples. The large Raman shift and the large width of the A_1g(O) imply rigid but distorted oxygen octahedral structure, therefore, the effect of nickel doping lowers the dielectric constant and the Q × f value of Ba(Mg_1/3Ta_2/3)O₃ ceramic.     

Synthesis and photoluminescence characterizations of Zn2+ and Tb3+ codoped CeO2 phosphors for temperature sensing applications

Cyan light-emitting Ce_0.985-xZn_xO₂:0.015 Tb³⁺ (x = 0 to 0.2) phosphors were synthesized using the ethylenediaminetetraacetic acid-assisted hydrothermal method. The X-ray diffraction and refinement analyses of the prepared phosphors indicated that the formed face-centered cubic structure remained intact even after the doping of large quantities of Zn²⁺ ions. However, the incorporation of Zn²⁺ ions increased the Ce³⁺/Ce⁴⁺ ratio, resulting in the enhancement of oxygen vacancies in the prepared phosphors. The generation of oxygen vacancies caused the evolution of a broad photoluminescence emission band ranging from 400 to 525 nm with a characteristic Tb³⁺ emission of approximately 543 nm. Two-emission regions in Ce_0.885Zn_0.1O₂:0.015 Tb³⁺ phosphors were utilized for measuring the fluorescence intensity ratio (FIR) as a function of temperature ranging from 303 to 523 K. At 523 K, the FIR values dropped to approximately 40% of the starting temperature value. The variation of FIR values followed the Boltzmann behavior. The Boltzmann fitting demonstrated the feasibility of the present phosphors for temperature sensor applications. The optimum absolute sensor sensitivity of Ce_0.885Zn_0.1O₂:0.015 Tb³⁺ phosphors was measured to be 0.0043 K⁻¹ at 398 K with a resolution of approximately 1 K⁻¹. Moderate temperature sensitivity, negligible hysteresis loop, and excellent reversibility revealed the suitability of Ce_0.885Zn_0.1O₂:0.015 Tb³⁺ phosphors for sensing the temperature in various electronic devices.     

Microwave dielectric properties of Ba8Ta6(Ni1 − xMx)O24 (M = Zn and Mg) ceramics

The influence of M (M = Zn and Mg) substitution for Ni on the microwave dielectric properties and the crystal structure of Ba₈Ta₆(Ni_1 − xM_x)O₂₄ ceramics was investigated in this study. The Ba₈Ta₆(Ni_1 − xZn_x)O₂₄ (BTNZ) solid solutions showed a single phase in the composition range of 0–1, whereas the limit of Ba₈Ta₆(Ni_1 − xMg_x)O₂₄ (BTNM) solid solutions was approximately x = 0.75; the lattice parameters of both solid solutions increased linearly, depending on the composition x. Although the dielectric constants (ɛ_r) of BTNZ were almost constant over the whole composition range, those of BTNM slightly decreased from 27.8 to 24.3; the decrease in the dielectric constant of BTNM is due to the change in relative density of the sample. The quality factors (Q × f) of both solid solutions were improved by the M substitution for Ni; the maximum Q × f values of BTNZ and BTNM were 91729 and 93127 GHz, respectively. Moreover, the temperature coefficients of resonant frequency (τ_f) of BTNZ and BTNM varied from 33 to 40 ppm/°C and from 33 to 26 ppm/°C, respectively.     

Chemical synthesis,compositional, morphological,structural, optical and magnetic properties of Zn1−xDyxS nanoparticles

Zn_1−xDy_xS (x=0, 0.02 and 0.04) nanoparticles (NPs) were synthesized by chemical refluxing technique at 100 °C. The prepared samples were analyzed by studying their compositional, morphological, structural, optical and magnetic properties. EDS analysis confirmed the presence of zinc, dysprosium and sulfur in the samples in near stoichiometric ratio. The X-ray diffraction patterns do not show any Dy related peaks for the as-synthesized ZnS nanoparticles. The average diameter of the particles confirmed by TEM studies, was in the range 2–4 nm. Raman studies revealed that all the samples are single phase and exhibit cubic structure. From DRS studies, the band-gap was found to be in the range of 3.85–3.70 eV. All the doped ZnS nanoparticles exhibit ferromagnetic behavior with the Curie temperature higher than room temperature and the magnetic properties of doped ZnS nanoparticles depend on the concentration of Dy ions.