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We successfully fabricated ZnO, Zn0.96Co0.04O, Zn0.95Co0.04Ce0.01O, Zn0.94Co0.04Ce0.02O, and Zn0.92Co0.04Ce0.04O nanoparticles and studied their room-temperature structure and magnetic properties. The X-rays diffraction (XRD) patterns of all the samples confirmed the presence of a wurtzite-type structure. XRD and Transmission Electron Microscopy (TEM) results showed that Zn2+ ions originally at tetrahedral sites were replaced by high-spin Co2+ and Ce3+ ions. This study also showed that with an increase in co-dopant concentration, the average grain size of the samples increased. We found that Zn0.96-xCo0.04CexO (x = 0.0, 0.1, 0.2, and 0.4) nanoparticles were ferromagnetic with a Curie temperature above 300 K. In addition, a large increase in ferromagnetism, i.e., high coercivity field, Hc, of 90Oe and remanent magnetization, Mr, of 0.25 × 10−2 emu/g, was observed for Zn0.96-xCo0.04CexO (x = 0.2) nanoparticles. The origins of ferromagnetism may be either due to the intrinsic nature of Co and Ce co-doped samples or to the presence of certain undetected spinel-type impurities in the samples. Also, it was concluded that Co and Ce incorporation are responsible for ferromagnetism in the doped sample. The doping generates oxygen vacancies, which trap charges and cause a rise in F-centers, resulting in exchange interactions with impurity atoms and increased magnetism. All these results showed that co-doped ZnO-based diluted magnetic semiconductors could be considered for spin-based electronics and optoelectronics devices.

We investigated the influence of oxygen vacancies (varying) on the structure and properties (dielectric and magnetic) of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles (NPs) fabricated using the chemical precipitation technique. The oxygen vacancies in the lattice increased with an increase in dopants (Co, Mn) concentration. Annealing of the doped nanoparticles decreased their dielectric properties due to reduced grain boundaries caused by enhanced grain growth. Replacement of Zn ions with dopants in the lattice enhanced the samples' electrical conductivities due to the reduction in grain boundaries and increase of charge carriers. The co-doped nanoparticles annealed at 600 °C exhibited some hysteresis loop changes and became ferromagnetic (FM). The magnetization increased with an increase in dopants content in the ZnO matrix, while coercivity decreased. This shows that the properties of the doped samples are strongly related to the number of oxygen vacancies. These results demonstrated that the enhanced dielectric and magnetization responses of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles are strongly correlated with the oxygen vacancies. The enhancement in optical, dielectric, and magnetic properties make transition metals (TM)-doped ZnO nanoparticles suitable for spintronics, and optoelectronic-based applications.

PurposeThin coatings are of great importance to minimize corrosion attack of steel in different environments. A review of recent work on electrodeposition and corrosion performance of Zn-Ni-based alloys for sacrificial corrosion protection of ferrous substrates is presented. The purpose of this study is to provide a systematic comparison of the corrosion resistances of Zn-Ni alloy coatings. The review contains key and outstanding comparisons of references for the period from 2007 to 2017. Binary and ternary Zn-Ni-based alloys were compared and contrasted to provide a good knowledge basis for selection of best coating system to steel substrates.Design/methodology/approachThis article is a review article.FindingsZn-Ni-(X) alloys show great potential for replacing Cd metal in corrosion protection of steel substrates.Practical implicationsThe research on plating of binary Zn-Ni alloys from aqueous electrolytes is now well advanced and these alloys show improved corrosion resistance compared to pure Zn. Pulse plated and compositionally modulated multilayer Zn-Ni alloy coatings showed enhanced corrosion properties compared to direct plated Zn-Ni coatings of similar composition.Originality/valueThe work on electrodeposition of Zn-Ni based alloys from ionic liquids is still scarce, yet these liquids show great promise in improving corrosion resistance and reducing coating thickness when compared to aqueous electrolytes. Advanced plating techniques in ionic liquids such as electromagnetic, compositionally modulated multilayer, pulse plating, ternary alloys and composites should be considered as these electrolytes avoid water chemistry and associated defects.

With the objective of obtaining corrosion resistant coatings, ternary Ni–Sn–P alloy coatings were electrodeposited from a deep eutectic solvent and their composition, morphology and corrosi...

The ZnO, Zn0.96Mn0.04O, Zn0.95Mn0.04Co0.01O, Zn0.94Mn0.04Co0.02O and Zn0.92Mn0.04Co0.04O nanoparticles were synthesized by simple chemical precipitation technique. The effects of co-doping on the structure and magnetic properties of these nanoparticles were studied. The X-rays diffraction (XRD) scans were performed in the 2θ range of 20°–80°. The XRD patterns, at 300 K, of all the pure and co-doped ZnO samples confirmed the formation of wurtzite-type structure. X-ray diffraction and transmission scanning electron microscope analysis indicated that the high spin Co2+ and Mn2+ ions were substituted for the Zn2+ ions at tetrahedral sites. The average size of the nanoparticles were increased from 17 to 24 nm with the increase of dopants concentration. Moreover, Energy Dispersive X-ray spectroscopy (EDX) confirmed the synthesis results. All Zn0.96−xMn0.04Co x O (x = 0.0, 0.1, 0.2 and 0.4) nanoparticles samples were observed to be paramagnetic below 300 K. However, a large increase in the magnetization was observed below 40 K. This behavior, along with the negative value of the Curie–Weiss constant obtained from the linear fit to the susceptibility data below room temperature, indicated the ferromagnetic nature of the samples. The origin of ferromagnetism is likely to be the intrinsic characteristics of the Co and Mn doped samples. The high magnetization was noted for the 1 wt% Co co-doped Mn–ZnO annealed samples as compared to other samples with Co concentration above and below this threshold concentration.

Pure and Zn0.98Ni0.02O nanostructures were prepared by the co-precipitation method. The effects of annealing in Argon (Ar) and oxygen (O2) environment on the structure, dielectric, electric and magnetic properties were investigated. The structural analysis from X-ray diffraction and energy dispersive X-ray results confirmed that all the nanoparticles samples indexed to hexagonal wurtzite ZnO structure. A significant decrease was observed in the dielectric constant (e r ) and dielectric loss (e′′) resulting from the incorporation of Ni into the ZnO lattice. Higher e r and e′′ were observed in the O2 annealed sample. Moreover, the AC electrical conductivity (α AC ) of the Ni doped ZnO sample increased in comparison with that of pure ZnO sample due to the increase of available charge carriers after replacement of Zn ions with Ni ions. The 2 wt% Ni-doped ZnO sample annealed in O2 and Ar environment revealed room temperature ferromagnetism (RTFM) behavior, but higher ferromagnetic was only observed in the O2 annealed sample. The origin of RTFM may originate from the exchange interaction between Ni 2+ and excess of O2 vacancy in Zn0.98Ni0.02O nanoparticles.

The rich island morphology of two-dimensional (2D) materials during chemical vapor deposition (CVD) growth process is studied using a computational model based on a Burton-Cabrera-Frank (BCF) type crystal growth theory. A previously formulated phase-field (PF) model for the BCF crystal growth process is employed to investigate the effect of various growth conditions, such as the concentration of absorbed atoms on the substrate and the growth temperature, that have been experimentally known to significantly impact the island morphology. It is shown that, within this simple model, the rich morphology of 2D islands in CVD growth can be well reproduced. With increasing substrate temperature, the 2D island changes from dendritic to compact shape. When considering the energy difference between the zigzag and the armchair edges of the 2D island, most commonly known morphologies, from quasi-sixfold compact islands to spiky triangular and compact triangular shapes, are observed in the model. Growth mechanisms associated with different island shapes and potential model improvements are also discussed.

The properties of Ti–Al–Nb alloys strongly depend on alloy compositions and microstructures. Proper design of these important aspects requires detailed knowledge of the solidification sequences and liquidus projection. However, there are still some conflicts between previous experimental and calculated results about the liquidus projections in the composition range of Ti-(40–60)Al-(5–30)Nb and this has hindered Ti–Al–Nb alloy development. In this present work, we explicitly investigated the as-cast microstructures and phase constitution of 50 alloys with the composition range of Ti-(40–60)Al-(5–30)Nb and clarified the solidification sequences. We re-constructed the partial liquidus projection and found that the primary β phase region extend to just below 55 at.% Al content and the primary α phase region extend to just below 24 at.% Nb content. Moreover, it was observed that the invariant reaction between Liquid, β, α and γ phases is a peritectic reaction (Liquid+β+γ→α) and all the Liquid+β+γ, Liquid+β+α and Liquid+α+γ three-phase regions are of peritectic type. The present work provides essential information necessary for optimizing the Ti–Al–Nb thermodynamic database to accelerate alloy development.

A highly valuable co-precipitation technique was used for the preparation of ZnO, Zn0.98Al0.02O and Zn0.96Al0.02Ni0.02O semiconductor nanoparticles. X-ray diffraction and scanning electron microscopy measurements reveal that the samples are nano-columns with a hexagonal wurtzite crystal structure. A significant enhancement in dielectric constant resulted from the substitution of (Al, Ni) co-doped ZnO lattice while an opposite trend was observed for dielectric loss. With the substitution of both Al and Ni, the electrical conductivity was found to be increased in comparison with that of ZnO nanoparticles due to the increase of available charge carriers after replacement of Zn ions by Ni ions. The magnetic property measurements revealed well room-temperature ferromagnetism, RTFM (Diluted magnetic semiconductor behavior) for the Ni co-doped samples in comparison with that of single Al–ZnO. The origin of high ferromagnetic may arise from the metallic Ni and intrinsic property of the doped ZnO.

The effect of annealing temperature on the dielectric and magnetic properties of (Co, Zn) co-doped SnO2 nanoparticles under air/oxygen (O2) and argon (Ar) atmospheres at 600 °C have been systematically investigated. A significant decrease is observed in dielectric constant and dielectric loss resulting from the incorporation of Co and Zn into the SnO2 lattice. Higher dielectric constant and loss was observed in the O2 annealed sample. Moreover, the electrical conductivity of the (Co, Zn) co-doped SnO2 samples increased in comparison with that of pure SnO2 sample due to the increase of available charge carriers after replacement of Sn ions with Co and Zn ions. Room-temperature ferromagnetism (RTFM) was observed for both the O2 and Ar annealed (Co, Zn) co-doped SnO2 samples. However, the remanent magnetization (Mr) varied drastically for different environmental annealing processes with Mr = 0.412 and 0.20 memu/g for the O2 and Ar-annealed samples, respectively. The results show that the enhanced dielectric and magnetic properties of (Co, Zn) co-doped SnO2 sample is strongly correlated with the increase in O2 vacancies. These findings not only demonstrate that (Co, Zn) co-doped SnO2 samples show tunable RTFM, but also suggests that RTFM can be influenced by introduction of O2 vacancies during O2 annealing.

After our discovery of room temperature ferromagnetism in the (Co, Ni) co-doped SnO2 nanoparticles by co-precipitation method, we successfully annealed all (Co, Ni) co-doped SnO2 diluted magnetic nanoparticles in air at 800 °C. The effect of annealing on dielectric and magnetic properties of (Co, Ni) co-doped SnO2 diluted magnetic nanoparticles was investigated. The as-synthesized (Co, Ni) co-doped SnO2 nanoparticles were annealed in air at 800 °C for 2 h in an electric furnace. The dielectric constant and dielectric loss values of all (Co, Ni) co-doped SnO2 samples decrease whereas, the electrical conductivity value increased with an increase in Ni co-doped concentration. Room temperature ferromagnetic behavior was observed in (Co, Ni) co-doped SnO2 samples. Increasing the Ni content up to 2 % leads to an increase ferromagnetic behavior and beyond that the ferromagnetic behavior decreased. A comparative study shows that (Co, Ni) co-doped SnO2 nanoparticles annealed in air at 800 °C have an excellent dielectric, magnetic properties and higher electrical conductivity than that of the (Co, Ni) co-doped SnO2 annealed in air at 600 °C, indicating that these nanoparticles can be used for high frequency devices, ultrahigh dielectric materials and spintronics.

In this work, the dielectric and magnetic properties of (Co, Ni) co-doped SnO2 nanoparticles were studied using ac impedance spectroscopy and magnetic properties measurement system or quantum design superconducting quantum interference device. Results showed that dielectric constant (e r ), dielectric loss (e″), and ac electrical conductivity (σ AC ) are strongly frequency dependent. A decrease in frequency was accompanied with an increase in e r and e″ values, whereas, a decrease in the dielectric constant was observed with the increase of Ni co-doping concentration. It was found that the dielectric constant and dielectric loss values decrease, whilst AC electrical conductivity increases with increase in co-doping concentration. Magnetization measurements revealed that the Ni co-doped SnO2 samples exhibits room temperature ferromagnetism. The results illustrate that (Co, Ni) co-doped SnO2 nanoparticles have an excellent dielectric, magnetic properties, and high electrical conductivity than those of co-doped samples reported previously, indicating that these (Co, Ni) co-doped SnO2 materials can be suitable for the purpose of high frequency device and spintronic applications.

The magnetic, dielectric and electrical properties of (Co, Zn) co-doped SnO2 nanoparticles were investigated. The polycrystalline samples of (Co, Zn) co-doped SnO2 nanoparticles were prepared using a co-precipitation method. X-ray diffraction confirmed that the (Co, Zn) co-doped SnO2 powder samples have the same tetragonal structure as pure SnO2 nanoparticles. The magnetization measurements revealed that the Zn co-doped SnO2 samples exhibit room temperature ferromagnetism. Magnetic hysteresis loops were observed at room temperature with high coercivity H c of 85 Oe and remanent magnetization M r of 0.412 memu/g for 1 wt% Zn co-doped sample. A decrease in the dielectric constant was observed with an increase in Zn doping content and frequency, at room temperature. It was found that the dielectric constant and dielectric loss values decrease, while AC electrical conductivity increases with increase in doping concentration and frequency. This study demonstrates that the (Co, Zn) co-doped SnO2 materials can be used for applications in ultrahigh dielectric materials and spintronics.

The phase transformation sequences and phase equilibria in Ti-47Al-20Nb and Ti-47Al-22Nb (at.%) alloys were investigated through experiments and computational (CALculation of PHAse Diagrams) techniques. Experiments to study nonequilibria phase transformations involved quenching the alloys from high temperature followed by composition and microstructure characterization. The computed results show that with increase in temperature, the α + β + γ tie-triangle phase region shifts towards low Nb content. On the contrary, experimental results show that with increase in temperature the tie-triangle of α + β + γ moves towards high Nb content. These changes are attributed to the expansion of the α phase region and corresponding changes of the primary α, β and γ phase regions with increase in temperature. In the experimentally studied alloys, a part of the α phase transformed to γ phase by massive transformation and most of the β phase transformed to γ phase in high Nb content alloys.

This article outlines the findings in the comparison of the influence of mechanical and electromagnetic stirring (EMS) on ingot long-term purity and uniformity during Ohno continuous casting (OCC). The magnitude of the average optimum velocity flow field and stirring parameters required to effectively purify aluminum ingots using mechanical stirring of the melt was determined and analyzed. Basing on the determined optimum mechanical flow field, electromagnetic parameters producing almost the same flow field near the interface were obtained through careful adjustments of parameters. Optimum parameters of the mechanical and EMS were obtained by numerically solving the solidification model coupled with either the multi-reference frame model (for mechanical stirring) or the magnetohydrodynamic model (for EMS) in CFD Fluent 6.3.26 software. For mechanical stirring, an optimum stirring intensity of 2 mm/min was determined whilst for EMS, the optimum magnetic field with an amplitude of 20 mT and a frequency of 2.7 Hz was determined, and these produced same magnitude optimum flow fields resulting in high-purity aluminum ingots. Comparison of the two methods showed that EMS is good in covering all the regions near the solid–liquid interface and is more effective in bulk melt mixing; thus it produces more uniform and purer ingots for longer casting times.

With the purpose of obtaining compositionally uniform ingots during Ohno continuous casting of a dilute industrial aluminum alloy through eliminating segregation due to convection, a magnetic field strength required to damp natural convection and suppress macrosegregation was numerically determined. This was achieved by solving conservation equations of continuity, momentum, energy and Maxwell’s equations in order to predict the magnetic field effects on flow field (determining macrosegregation). The electromagnetic field was applied orthogonally to the natural convection flow. Through this approach, the optimum magnetic field strength required to damp natural convection and establish diffusion controlled solute transport of the alloy during solidification was established.

With the purpose of upgrading the purity of a dilute industrial aluminum alloy during Ohno Continuous Casting (OCC) process through the use of forced melt stirring; the critical stirring intensity required under a casting speed of 2 mm/min was numerically determined. The determined critical stirring intensity induces convective velocity magnitudes into the melt which are effective in transporting solutes from the solute boundary layer into the bulk melt. It was found that, with adequate melt stirring, production of substantially long and high purity ingots during OCC is possible before their purity diminishes to lower than the initial alloy purity.