CoO Doping Research Articles

Probing of CoO-induced nano-sized defects in Li2SO4–MgO–P2O5 glasses: Insights from positron annihilation lifetime spectroscopy

This study investigates the influence of CoO doping on concentration and characteristics of nano-sized cavities in Li₂SO₄-MgO-P₂O₅ glasses using positron annihilation lifetime spectroscopy (PALS). These defects are known to significantly impact the physical properties of glasses. Glasses with compositions of 20 Li₂SO₄-20MgO-(60-x) P₂O₅: x CoO (0 ≤ x ≤ 1.0 mol%), were prepared using melt-quench technique. PALS analysis revealed a strong dependence of positronium (e⁺- e⁻ pair) lifetime on CoO concentration. The analysis of the results further indicated that the fraction of free volume Δf/f0) and cavity radius (R) reached minimum values between 0.6 and 0.8 mol% CoO, but increased with further CoO doping. This suggests that cobalt ions prefer Oh sites, act as network modifiers, and create a larger concentration of free volume defects when CoO is increased beyond 0.8 mol%. Notably, the PALS-derived free volume defect concentration with CoO concentration is found to follow nearly same trend exhibited by the results of optical absorption and AC conductivity studies.

Mechanistic study of chemical looping partial oxidation of methane over Ce2(SO4)3/MgO with CoO modification

Chemical looping partial oxidation of methane (CLPOM) to syngas provides an exceptional opportunity for methane utilization. However, it is still urgent to obtain efficient oxygen carrier (OC) and clarify its microscopic mechanism. In this work, CoO and MgO modified Ce2(SO4)3 OC are optimized based on various preparation methods and different CoO and Ce2(SO4)3 doping amount. Considering the conversion rate (XCH4), selectivities of CO (SCO) and H2 (SH2), H2/CO molar ratio, when the doping amount of CoO, Ce2(SO4)3 and MgO is 20 wt%, 30 wt% and 50 wt% respectively, the OC prepared by mechanical ball milling method has a better thermodynamic and kinetic properties in chemical looping reaction. Compared with literature, this OC has a larger XCH4. In multiple cycles, XCH4 is still higher than 90%, SCO and SH2 remain above 95%. Density functional theory calculation reveal that the Co doping reduces the energy barrier (Eb) of rate-limiting step by 24.3% and lowers the migration Eb of lattice oxygen by 78.2%. The OC with oxygen vacancy can further reduce the Eb of rate-limiting step, but the Eb basically remains unchanged when the oxygen vacancy (Ov) concentration is greater than 1.96%. Because of the high Eb of CO2 formation and low Eb of syngas formation, the syngas demonstrates high selectivity and does not produce CO2 in experiment. Meanwhile, the doping of CoO and MgO reduces carbon deposition, refines the nano-particles of OC, increases the specific surface area (SSA), and enhances resistance to sintering and aggregation. The unique pore structure also provides a favorable microenvironment for the reaction. These findings demonstrate that CoO and MgO modified Ce2(SO4)3 OC have the potential for application in CLPOM, and these basic insights can also be applied to other chemical looping systems.

Tuning of smart cobalt doped borate glasses by electron beam as band-pass filters

CoO (0.2, and 0.7 wt%) doped lithium borate glass samples according to the composition of 84 % B2O3 + 12 % Li2O + 4 % Al2O3 have been prepared by melt quenching technique. Archimedes's method was used to compute the molar volumes of the formed glasses by measuring their density. For the purpose of analyzing the band-pass glass filter and UV-IR cut-off, the optical spectroscopic features of the obtained lithium borate glasses were evaluated over the entire wavelength range from 190 to 1100 nm. The effect of CoO doping ratios (0.2, and 0.7 wt%) on the optical properties of the prepared glass samples (refractive index, optical and electrical conductivity, reflection loss (RL), optical transmission (Toptical), extinction coefficient, permittivity, dielectric constants, electric susceptibility and polarizabilities) were studied. The decrease in ETauc and increase in UV–Visible cutoff range with the increase of CoO content is due to the increase of the non-bridging oxygen concentration. Co2+ ions are detected in both tetrahedral and octahedral positions in the glass matrix, according to the electron paramagnetic resonance EPR spectra. The transmittance data of the glass filters revealed that they have a broad band-pass in the Vis-NIR region. The electron beam irradiation showed an increase in the stopping range of the prepared glasses as band pass filters which makes them available for a wide-range of optical equipment including lenses and laser shields, as well as optoelectronic and photovoltaic apparatus.

Microstructure and performance characterization of in-situ Co2FeO4 whiskers reinforced YIG/YIG joints

Bismuth-based glasses doped with different CoO contents were designed to realize the in-situ growth of Co2FeO4 whiskers in YIG/YIG joint. The microstructure, mechanical and dielectric properties of the joints were systematically investigated. The optimized processing joint with 23 mol% CoO doping, brazed at 725 °C for 15 min, under bonding pressure of 6 kPa was achieved. And the shear strength of joint reached a maximum of 72 MPa, which is attributed to the increased number and optimized spatial distribution of Co2FeO4 whiskers. The in-situ Co2FeO4 whiskers acted as effective hard phases in the glass matrix. The shear strength of YIG/YIG joint was enhanced by the crack propagation deflection and pulling out result from Co2FeO4 whiskers. The dielectric constant of YIG joints decreased from 16.2 to 15.3 at the frequency of 10 MHz, which is closer to that of the original YIG material with the CoO doping increasing. The dielectric loss tangent increased slightly with the growth of Co2FeO4 whiskers due to the hole hopping between Co3+⇔Co2+ ions. The effective bonding of YIG materials has broad application prospects for the integration of ferrite microwave devices.

Preparation and characterization of CoO-doped and Li2O-stabilized Na-β″-Al2O3 solid electrolyte via a solid-state reaction method

The Na-β"-Al2O3 solid electrolyte ceramic material doped with CoO was synthesized via a solid-state reaction method, which began with α-Al2O3 and Na2CO3 as the raw materials and involved a low-cost burying process. The effects of different contents of CoO on the properties of the material were investigated as Li2CO3 was added as a stabilizer. The CoO amount in the initial materials is the key to obtaining quality products. Therefore, samples sintered from precursors containing different amounts of CoO were systematically characterized using thermogravimetry/differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). Additionally, the relative density and electrical properties of the prepared samples were also measured by the Archimedes method and AC impedance spectroscopy. The Na-β"-Al2O3 solid electrolyte with an optimal amount of CoO of 1 wt% exhibited a uniform and dense microstructure with a relative density of as much as 97.98% (3.194 g cm⁻3) of the theoretical density. However, excess 1.25 wt% CoO doping can cause the sample too loose and make pores between the grains larger. This deteriorates the ionic conductivity of the material. In addition, the sample with the appropriate amount of CoO exhibited an ionic conductivity of up to 0.061 S cm−1 at 300 °C with a corresponding activation energy of 0.179 eV.

Structural and Optical Study of CoO Doping in Borophosphate Host Glass and Effect of Gamma Irradiation

A series of borophosphate based glasses were prepared with a main composition (50P2O5–30B2O3–10CaO–10Na2O ) wt%. The effect of addition wt% (of cobalt oxide (0.2, 0.5, 0.7) g in different forms is the main purpose of this study. Structural and optical properties of the prepared glasses were obtained using both FITR and UV–Visible techniques. The optical band gap was evaluated from the optical absorption spectral data. XRD was investigated to indicate the formed phases of prepared systems. Density measurements also were done using Archimedes method. The effect of successive gamma irradiation by various doses (10, 30, 50 KGy not) on the different properties of the prepared glasses were measured.

Ferroelectric, Piezoelectric and Dielectric Behaviors of CoO‐ and Fe2O3‐Doped BCZT Ceramics

This study investigates the effect of CoO and Fe2O3 dopant on phase, microstructure and ferroelectric properties of BCZT ceramics with the formula of Ba0.85Ca0.15Zr0.1(Ti1‐xCox)0.9O3 and Ba0.85Ca0.15Zr0.1(Ti1‐xFex)0.9O3 where x = 0, 0.01, and 0.03. The XRD patterns presented that the pure perovskite phases are observed regardless of the amount of CoO and Fe2O3 added. Rietveld analysis shows that the tetragonal phase is observed in all patterns and the unit cell volume slightly expanded by the CoO addition while it is distorted with increasing Fe2O3 addition. The average grain sizes decreased upon CoO and Fe2O3 addition. It is found that the doping of CoO and Fe2O3 caused the transition temperature to shift to lower temperature. The optimum ferroelectric and dielectric properties can be achieved for the BCZT‐0.01Co ceramics. This study shows that while small doping with Co and Fe can enhance different properties of BCZT with lower processing temperature, the properties should be further optimized by chemical modification.

Efficient Removal of Methane over Cobalt-Monoxide-Doped AuPd Nanocatalysts

To overcome deactivation of Pd-based catalysts at high temperatures, we herein design a novel pathway by introducing a certain amount of CoO to the supported Au-Pd alloy nanoparticles (NPs) to generate high-performance Au-Pd-xCoO/three-dimensionally ordered macroporous (3DOM) Co3O4 (x is the Co/Pd molar ratio) catalysts. The doping of CoO induced the formation of PdO-CoO active sites, which was beneficial for the improvement in adsorption and activation of CH4 and catalytic performance. The Au-Pd-0.40CoO/3DOM Co3O4 sample performed the best (T90% = 341 °C at a space velocity of 20 000 mL g-1 h-1). Deactivation of the 3DOM Co3O4-supported Au-Pd, Pd-CoO, and Au-Pd-xCoO nanocatalysts resulting from water vapor addition was due to the formation and accumulation of hydroxyl on the catalyst surface, whereas deactivation of the Pd-CoO/3DOM Co3O4 catalyst at high temperatures (680-800 °C) might be due to decomposition of the PdOy active phase into aggregated Pd0 NPs. The Au-Pd-xCoO/3DOM Co3O4 nanocatalysts exhibited better thermal stability and water tolerance ability compared to the 3DOM Co3O4-supported Au-Pd and Pd-CoO nanocatalysts. We believe that the supported Au-Pd-xCoO nanomaterials are promising catalysts in practical applications for organic combustion.

The effect of bimodal model on the ultra-broad temperature stable BaTiO3–Na0.5Bi0.5TiO3–Nb2O5 system

A new lead-free, high dielectric constant, wide temperature stable dielectric ceramics was prepared by traditional solid-state method. The phase contribution, electric and dielectric properties of the BaTiO3–Na0.5Bi0.5TiO3–Nb2O5 ceramics were investigated. The bimodal model was proposed to explain the phenomenon of ultra-broad temperature stable. The doping of CoO played a decisive role in the realization of a wide temperature range of −50–350°C stability. In addition, a relative higher dielectric constant and lower dielectric loss (εr=1365±15%, tanδ=1.513%) were obtained. These features suggest that the ceramics system can be considered as a promising candidate material for the next generation of MLCC.

CoO doping effects on the ZnO films through EBPDV technique

Nanometric Zn1−xCox O( x = 0.020, 0.025 and 0.030 in mol.%) nanopowders were obtained from low temperature calcination of a resin prepared using the Pechini's method. Firing the Zn1−xCoxO resin at 400 ◦ C/2 h a powder with hexagonal structure was obtained as measured by X-ray diffraction (XRD). The powder presented average particle size of 40 nm observed by field emission scanning electronic microscopy (FE-SEM) micrographs and average crystallite size of 10 nm calculated from the XRD using Scherrer's equation. Nanocrystalline Zn1−xCoxO films with good homogeneity and optical quality were obtained with 280-980 nm thicknesses by electron beam physical vapour deposition (EBPVD) under vacuum onto silica substrate at 25 ◦ C. Scanning electron microscopy with field emission gun showed that the film microstructure is composed by spherical grains and some needles. In these conditions of deposition the films presented only hexagonal phase observed by XRD. The UV-visible-NIR and diffuse reflectance properties of the films were measured and the electric properties were calculated using the reflectance and transmittance spectra.

Evolution of structural and electrical properties of (K,Na,Li)(Nb,Ta,Sb)O 3 lead-free piezoceramics through CoO doping

Doping with transition metals is widely used for piezoceramic improvement. In this work, we study the effects of cobalt doping on the properties of the well known (K,Na,Li)(Nb,Ta,Sb)O 3 piezoelectric ceramics. Two different situations were observed: for low concentrations, Co 2+ cations occupy the A-site of the perovskite structure, whereas for high concentrations they occupy the B-site. The piezoelectric properties of the material are slightly affected with the cobalt concentration, whereas the mechanical quality factor increases by a factor of nearly three.

SnO2-based varistors capable of withstanding surge current

SnO2-based varistor material was fabricated by doping of CoO, Nb2O5, Cr2O3, and Y2O3 or Ho2O3. The microstructure, nonlinear I-V characteristic and surge current performances have been investigated. The average grain boundary voltage of the obtained materials is close to that of ZnO varistors. Similar to Cr3+, Y3+ or Ho3+ acts as the acceptor in the grain boundaries and the depletion layers. Moderate co-doping Y2O3 or Ho2O3 with Cr2O3 is helpful to improve the electrical performances and to prevent poor densification. The obtained optimal samples with a diameter of about 14 mm have a nonlinear coefficient (α) of about 60, threshold electric field (Eb) of about 380 V/mm, and the withstanding peak current of 8/20 μs wave is about 2400 A. Higher surge current will cause failure but no visual damage happen. This kind of failure mode is helpful for safety use of varistors.

Electrical barriers formation at the grain boundaries of Co-doped SnO 2 varistor ceramics

The nonlinear electrical properties of CoO-doped SnO 2 ceramics were characterized. A second phase is observed at the surface of the microstructure of the specimens. Energy-dispersive X-ray analysis reveals that the second phase is composed of tin, cobalt and oxygen with an approximate atomic ratio estimated for Co and Sn: 2:1. The phase was identified by X-ray diffraction and unambiguously establish the identity of the phase: Co 2SnO 4. Electrical characterization of the binary CoO–SnO 2 was carried out on a very large range of current from 10 −9 up to 100 A cm −2 showing that the doping of CoO increases drastically the resistivity of the ceramic from 10 4 to 10 10 Ω cm. This value appears to be a threshold for which the nonlinear effect appears.

Origin of the large thermoelectric power in oxygen-variableRBaCo2O5+x(R=Gd,Nd)

Thermoelectric properties of GdBaCo_{2}O_{5+x} and NdBaCo_{2}O_{5+x} single crystals have been studied upon continuous doping of CoO_2 planes with either electrons or holes. The thermoelectric response and the resistivity behavior reveal a hopping character of the transport in both compounds, providing the basis for understanding the recently found remarkable divergence of the Seebeck coefficient at x=0.5. The doping dependence of the thermoelectric power evinces that the configurational entropy of charge carriers, enhanced by their spin and orbital degeneracy, plays a key role in the origin of the large thermoelectric response in these correlated oxides.

Electron-Hole Asymmetry inGdBaCo2O5+x: Evidence for Spin Blockade of Electron Transport in a Correlated Electron System

In RBaCo2O(5+x) compounds (R is rare earth), the variability of the oxygen content allows precise doping of CoO2 planes with both types of charge carriers. We study transport properties of doped GdBaCo2O(5+x) single crystals and find a remarkable asymmetry in the behavior of holes and electrons doped into a parent insulator GdBaCo2O(5.5). The doping dependencies of resistivity, Hall response, and thermoelectric power reveal that the doped holes greatly improve the conductivity, while the electron-doped samples always remain poorly conducting. This doping asymmetry provides strong evidence for a spin blockade of the electron transport in RBaCo2O(5+x).

Transport and magnetic properties ofGdBaCo2O5+xsingle crystals: A cobalt oxide with square-latticeCoO2planes over a wide range of electron and hole doping

Single crystals of the layered perovskite GdBaCo_{2}O_{5+x} (GBCO) have been grown by the floating-zone method, and their transport, magnetic, and structural properties have been studied in detail over a wide range of oxygen contents. The obtained data are used to establish a rich phase diagram centered at the "parent'' compound GdBaCo_{2}O_{5.5} -- an insulator with Co ions in the 3+ state. An attractive feature of GBCO is that it allows a precise and continuous doping of CoO_{2} planes with either electrons or holes, spanning a wide range from the charge-ordered insulator at 50% electron doping (x=0) to the undoped band insulator (x=0.5), and further towards the heavily hole-doped metallic state. This continuous doping is clearly manifested in the behavior of thermoelectric power which exhibits a spectacular divergence with approaching x=0.5, where it reaches large absolute values and abruptly changes its sign. At low temperatures, the homogeneous distribution of doped carriers in GBCO becomes unstable, and both the magnetic and transport properties point to an intriguing nanoscopic phase separation. We also find that throughout the composition range the magnetic behavior in GBCO is governed by a delicate balance between ferromagnetic (FM) and antiferromagnetic (AF) interactions, which can be easily affected by temperature, doping, or magnetic field, bringing about FM-AF transitions and a giant magnetoresistance (MR) phenomenon. An exceptionally strong uniaxial anisotropy of the Co spins, which dramatically simplifies the possible spin arrangements, together with the possibility of continuous ambipolar doping turn GBCO into a model system for studying the competing magnetic interactions, nanoscopic phase separation and accompanying magnetoresistance phenomena.

Dielectric property–microstructure relations in Co-O doped (Y2−xSmx)BaCuO5 ceramics

The effect of CoO doping on the microwave dielectric property and the microstructure of (Y 2− x Sm x )BaCuO 5 ceramics have been investigated. The limits of the (Y 2− x Sm x )Ba(Cu 1− y Co y )O 5 ( x =0,1 and 2) solid solutions were approximately y =0.1 and the deviations of the valences in cations determined by using bond valence sum may be related to the formation of the solid solutions. It was found that high Q · f values were obtained by the Co substitution for Cu in the (Y 2− x Sm x )BaCuO 5 ceramics, whereas the τ f values were not improved. In the Sm-substituted (Y 2− x Sm x )Ba(Cu 1− y Co y )O 5 ceramics, the optimum value of τ f which was closest to 0 ppm/°C was −6.3 ppm/°C for x =2. The reduction of porosity in the Sm 2 Ba(Cu 1− y Co y )O 5 ceramics at compositions lower than y =0.01 was recognized; it was found that these morphological changes in the ceramics were closely related to the increase of the Q · f values. Thus, the optimum dielectric properties, i.e. ε r =16.8, Q · f =90732 GHz and τ f =−9.2 ppm/°C, were obtained in the Sm 2 Ba(Cu 0.99 Co 0.01 )O 5 ceramics by using cold isotropic pressing (CIP).

On some properties of NASICON doped with MgO and CoO

The influence of MgO or CoO doping on the chemical composition and on the electrical conductivity of NASICON ceramics was studied. It was found that the grain and intergrain electrical conductivities behave differently as a function of doping rate and the kind of dopant.

Enhancement of Electrical Conduction in ZnO by CoO Doping

Electrical conductivity of sintered ZnO was increased at high temperatures by CoO doping. Thermoelectric power measurements confirmed that ZnO doped with CoO was still an n‐type semiconductor. Temperature‐independent behavior of the carrier density was observed.

The Oxidation of a Monophase Co-8.03 Wt% Cu Alloy at 700 to 1000 C

Abstract The oxidation of a monophase cobalt-copper alloy at high temperature has been Studied to examine the effect of the copper addition to cobalt on the oxidation kinetics as well as on the scale morphology and composition. The rate law remains parabolic as for pure cobalt but the rate constant is higher at all temperatures. This result is interpreted as being due mainly to the doping of CoO by monovalent copper ions by means of a detailed calculation of the rate constant for the alloy making use of the experimental profile of the copper concentration in the scale and of a suitable model for the defect structure of cobalt oxide.