Co-doping Of Co Research Articles

Regulating the 3d-orbital occupancy on Ni sites enables high-rate and durable Ni(OH)2 cathode for alkaline Zn batteries

The capacity and cycling stability of β-Ni(OH)2-based cathodes in aqueous alkaline Ni-Zn batteries are still unsatisfactory due to their undesirable OH− adsorption/desorption dynamics during the electrochemical redox process. To settle this issue, we introduce a new atomic-level strategy to finely modulate the OH− adsorption/desorption of β-Ni(OH)2 through tailoring the 3d-orbital occupancy of Ni center by Co/Cu co-doping (denoted as Co-Cu-Ni(OH)2). Both experimental outcomes and density functional theory calculations validate that the co-doping of Co and Cu endows the Ni species in Co-Cu-Ni(OH)2 with appropriate proportion of the unoccupied 3d-orbital, leading to optimized adsorption/desorption strength of OH−. As anticipated, the Co-Cu-Ni(OH)2 electrode demonstrates superior performance, achieving an areal capacity of 0.83 mAh cm−2 and a gravimetric capacity of 164.3 mAh g−1 at ∼50 mA cm−2 (10 A g−1). Furthermore, it sustains an impressive capacity of 170.8 mAh g−1 (2.3 mAh cm−2) at a high mass loading of 13.5 mg cm−2, alongside a long-term cycling performance over 1000 cycles. The assembled Co-Cu-Ni(OH)2//Zn cell is able to provide a peak energy density of 0.98 mWh cm−2 and excellent durability. This work highlights the potential of an orbital engineering strategy in the development of next-generation high-capacity and durable energy storage materials.

Highly catalytic performance for the selective C–H bond oxidation of p-chlorotoluene over Co, Cr co-doped OMS-2 catalyst

Using O2 as an oxidant, developing a non-noble metal catalyst for the selective catalytic C–H bond oxidation of p-chlorotoluene is desirable and challenging. In this work, a series of Co, Cr co-doped OMS-2 (Octahedral Molecular Sieve-2) catalysts were prepared by a conventional refluxing method. It was found that the incorporation of Co and Cr improved the catalytic activity for the selective oxidation of p-chlorotoluene to p-chlorobenzaldehyde. Among these catalysts, CoCr/OMS-2 (Co: Cr = 1: 1, mass ratio), the best catalyst, shows that the conversion and the selectivity of p-chlorobenzaldehyde is 94.8 % and 94.3 %, respectively. The enhanced catalytic activity was due to the larger specific surface area and even dispersion of active components. The characterization results also disclosed that the co-doping of Co and Cr increased the oxygen vacancy and enhanced the ability to activate the surface lattice oxygen. Additionally, density functional theory calculations demonstrated that co-doping of Co and Cr promoted the adsorption of p-chlorotoluene and O2, and decreased the energy barrier of rate-determining step (the conversion of p-chlorobenzyl alcohol to p-chlorobenzaldehyde). Besides, when H2O was added to the reaction system as the second solvent, the activation and dissociation of O2, and the formation of p-chlorobenzaldehyde were facilitated, in agreement with the experimental results. This work demonstrated the promotional effect of Co, Cr co-doped into OMS-2 catalyst and the role of H2O for the selective oxidation of p-chlorotoluene.

Enhanced Visible-Light-Assisted Photocatalytic Removal of Tetracycline Using Co/La@g-C3N4 Ternary Nanocomposite and Underlying Reaction Mechanisms

Graphitic carbon nitride (g-C3N4) is a promising material for photocatalytic applications. However, it suffers from poor visible-light absorption and a high recombination rate of photogenerated electron–hole pairs. Here, Co/La@g-C3N4 with enhanced photocatalytic activity was prepared by co-doping Co and La into g-C3N4 via a facile one-pot synthesis. Co/La@g-C3N4 displayed better performance, achieving 94% tetracycline (TC) removal within 40 min, as compared with g-C3N4 (BCN, 65%). It also demonstrated promising performance in degrading other pollutants, which was ~2–4-fold greater relative to BCN. The improved photocatalytic activity of Co/La@g-C3N4 was associated with improved photogenerated charge separation, reduced charge transfer resistance, a built-in electric field arising from the p-n-p heterojunction, and the synergistic effect of ternary components for the separation and transfer of the photogenerated charge carriers. Superoxide radicals are suggested to be the most notable reactive species responsible for the photocatalytic reaction. Environmental factors, including the pollutant concentration, catalyst dosage, solution pH, inorganic salts, water matrices, and mixture with dyes, were considered in the photocatalytic reactions. Co/La@g-C3N4 showed good reusability for five cycles of the photocatalytic degradation of TC. The facile one-pot co-doping of Co and La in g-C3N4 formed a p-n-p heterojunction with boosted photocatalytic activity for the highly efficient removal of TC from various water matrices.

Efficient activation of peroxymonosulfate by molybdenum disulfide cocatalysis of Co and N co-doped porous carbon for degrading perfluorooctanoic acid: Synergistic effect of Co and N by molybdenum and its mechanism

In this study, precursor ultrathin molybdenum disulfide nanosheets and ZIF-67 was selected to prepare Co and N co-doped porous carbon by the support of Mo (MoS2/Co@NPC) to activate peroxymonosulfate (PMS) for perfluorooctanoic acid (PFOA) degradation. The morphology, crystal form and composition of MoS2/Co@NPC are studied by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and other methods. In MoS2/Co@NPC/PMS process, PFOA was completely degraded in 180 min at pH 7, 0.3 g/L catalyst, 0.1 mM PMS and reaction temperature of 25 °C. The degradation efficiency was much higher than that in other systems. The oxidative species for PFOA degradation was studied using free radical quenching experiments and electron paramagnetic resonance (ESR) tests. SO−4 plays a major role in the degradation of PFOA, OH plays an auxiliary role, and 1O2 contributes the least. The effect of different types and positions of cobalt‑nitrogen and molybdenum atoms on the electrocatalytic activity was investigated by density functional theory (DFT) calculations. The co-doping of Co and N into carbon-based materials can synergistically enhance by Mo for the activation of PMS. The unsaturated S atoms on the surface of metal sulfides can trap protons to form H2S while exposing the reducing metal active site, which also accelerates the rate-limiting step of the Co3+/Co2+ conversion. The core-shell structure of Co@NPC doped with Mo has the characteristics of improving the electron transfer ability of carbon, promoting the mass transfer of reactants, and preventing cobalt metal agglomeration and metal dissolution. The degradation pathways of PFOA were investigated and three possible pathways were proposed. In addition to PFOA, MoS2/Co@NPC-800/PMS system can also remove contaminant in pharmaceutical wastewater, indicating that the process has potential application value in practical wastewater treatment.

Construction active sites in nickel sulfide by dual-doping vanadium/cobalt for highly effective oxygen evolution reaction

Rational design and exploration of oxygen evolution reaction (OER) electrocatalysts with exceptional performance are crucial for the advancement of the hydrogen energy economy. In this study, vanadium/cobalt (V/Co) dual-doped nickel sulfide (Ni3S2) nanowires were synthesized on a nickel foam (NF) substrate to overcome the sluggish kinetics typically associated with OER. The resulting catalyst exhibited outstanding electrocatalytic activity towards OER in a 1.0 M KOH electrolyte, with a minimal overpotential of 155 and 263 mV, the current densities of 10 and 100 mA cm−2 can be achieved effortlessly. Importantly, this catalyst demonstrated remarkable stability over extended periods, maintaining its performance for 25 h under constant current density, 55 h under continuously varying current density, and even after undergoing 2000 cycles of cyclic voltammetry (CV), which had surpassed those of most non-noble metal electrocatalysts. The X-ray photoelectron spectroscopy and density functional theory analyses confirmed that the co-doping of Co and V redistributed the electron of Ni, leading to improvements in the d-band center, structural characteristics, and free energy landscapes of adsorbed intermediates. This work presents a novel strategy, based on the connection between electronic structure and catalytic properties, in the design of double-doped catalysts for efficient OER.

Co/Fe co-doped ZIF-8 derived hierarchically porous composites as high-performance electrode materials for Cu2+ ions capacitive deionization

Due to a threat to human life from heavy metal ions pollution, unprecedented interest has been gained in the development of water purification technologies. Here, we explore another new approach to exploit a prospective carbon material for removing copper ions from aqueous solution based on rapid and easy capacitive deionization (CDI). Reasonable carbon materials modification with ideal composition and improved morphological structure is essential to additionally optimize the capabilities of CDI. We prepared a nitrogen-rich hierarchically porous carbon composites (CoFe-NC) with uniform cobalt (Co) and iron (Fe) doped metal in carbon skeleton by a simple impregnation and pyrolysis method, derived from zeolitic imidazolate framework-8, to use as highly effective CDI electrode for copper ions removal. The addition of Fe can facilitate the uniform dispersion of metals, and enable the formation of a stable carbon cage after pyrolysis. It can sufficiently expose active sites of the electrode materials and promote interfacial charge transfer, thus improving CDI electrosorption efficiency. CoFe-NC composites electrode can achieve outstanding deionization capacity (91.31 mg g−1) in 25 mg L−1 CuSO4 solution. The carbon cage structure of CoFe-NC not only prevents aggregation of metals and avoids destruction of rich multistage pore system by pyrolysis, but also induces a faster ions transport rate. In addition, density functional theory calculations demonstrated that the co-doping of Co and Fe can remarkably increase the adsorption energies of Cu2+ ions, leading to excellent selectivity, which indicates that CoFe-NC composites can be a desired CDI electrode material.

Enhancement of electrical conductivity, optical band gap and ferromagnetic properties by co-doping of Co and Ti ions in canted antiferromagnetic hematite (α-Fe2O3) system

The Co and Ti ions have been co-doped at the sites of Fe3+ ions of α-Fe2O3 (hematite) structure by employing mechanical alloying technique and post heat treatment of the as-alloyed material under vacuum and air. The ratio of Co and Ti ions has been maintained at 50:50 in order to compensate charge disproportionate effect in the composition of α-Fe2-xTix/2Cox/2O3 (x = 0.2, 0.4, 0.6). The X-ray diffraction pattern and Raman spectra at room temperature have confirmed the formation of hematite (rhombohedral) structure as the major phase and a minor amount of TiO2 phase in some of the prepared samples. X-ray photoelectron spectra (XPS) have provided useful information of the chemical environment and electronic charge state of the metal (Co, Ti, Fe) ions in the lattice structure. The XPS spectra confirmed tetra-valence charge state of Ti ions, whereas a mixed valence charge state of Fe3+(Co2+) and Fe(2+δ)+(Co(3−δ)+) has been indicated for the Fe and Co ions. The mixed valence charge states indicated the enhancement of covalent character of the metal-oxygen bonds. In this work, details of the lattice structure, chemical composition, charge state of ions, optical, electrical and magnetic properties have been presented.

In Situ Fabrication of Highly Dispersed Co-Fe-Doped-δ-MnO2 Catalyst by a Facile Redox-Driving MOFs-Derived Method for Low-Temperature Oxidation of Toluene.

Cost-efficient and durable manganese-based catalysts are in great demand for the catalytic elimination of volatile organic compounds (VOCs), which are dominated not only by the nanostructures but also by the oxygen vacancies and Mn-O bond in the catalysts. Herein, a series of nanostructured Co-Fe-doped-δ-MnO2 catalysts (Co-Fe-δ-MnO2) with high dispersion were in situ fabricated by employing metal-organic-frameworks (MOFs) as reducing agents, dopants, and templates all at the same time. The as-obtained Co-Fe-δ-MnO2-20% catalyst exhibited robust durability and high catalytic activity (225 °C) for toluene combustion even in the presence of 5 vol % water vapor, which is 50 °C lower than that of pristine δ-MnO2. Various characterizations revealed that the homogeneously dispersed codoping of Co and Fe ions into δ-MnO2 promotes the generation of oxygen vacancies and weakens the strength of the Mn-O bond, thus increasing the amount of adsorbed oxygen (Oads) and improving the mobility of lattice oxygen (Olatt). Meanwhile, due to successfully inheriting the framework structures of MOFs, the obtained catalyst exhibited a high surface area and three-dimensional mesoporous structure, which contributes to diffusion and increases the number of active sites. Moreover, in situ DRIFTS results confirmed that the toluene degradation mechanism on the Co-Fe-δ-MnO2-20% follows the MVK mechanism and revealed that more Oads and high-mobility Olatt induced by this novel method contribute to accumulating and mineralizing key intermediates (benzoate) and thus promote toluene oxidation. In conclusion, this work stimulates the opportunities to develop Co-Fe-δ-MnO2 as a class of nonprecious-metal-based catalysts for controlling VOC emissions.

Purposefully designing Co-S-codoping in hierarchical BiOCl architectures and elucidating the mechanism for enhanced visible-light-driven photocatalytic activity

Simultaneously doping metal and nonmetal species into BiOCl photocatalysts is an efficient way to tailor the valence band and conduction band for enhanced both solar light harvesting and photocharge separation. However, the investigation on metal-nonmetal codoping of BiOCl photocatalysts is still less so far. Herein, the codoping of Co and S species into hierarchical BiOCl architectures (denoted as BOC-Co-S) is realized by a simple one-pot hydrothermal method. The as-prepared BOC-Co-S samples demonstrated remarkably high-efficient visible-light-driven photocatalytic performances toward the degradation of Rhodamine B and tetracycline compared with the Co-doped BiOCl, S-doped BiOCl and pure BiOCl samples. The improved photodegradation activities of BOC-Co-S samples can be ascribed to the increased solar light harvesting, efficient charge separation and sufficient activity sites derived from Co-S codoping. This study might provide a promising strategy to further explore simple and economic organic-free routes for the development of high-active bismuth oxyhalides-based photocatalysts.

Boosting activation of peracetic acid by Co@mZVI for efficient degradation of sulfamethoxazole: Interesting two-phase generation of reactive oxidized species

Developing a cost-effective, easy-recycled, pH-independent and efficient activator is promising for the practical application of peracetic acid (PAA) based advanced oxidation process (AOP). In this study, Co@mZVI was synthesized to activate PAA for successful degradation of 96% sulfamethoxazole (SMX) within 30 min, while only 40% of the SMX could be removed in the mZVI/PAA system. Co-doping of Co extended the pH tolerance of mZVI as indicated by 90%-98% SMX removal efficiency at the initial pH range of 3.0–9.0. Reactive oxidized species (ROS) including organic radicals, hydroxyl radical (•OH) and Fe(IV) were produced from the Co@mZVI/PAA system. It’s found that the co-doped Co can 1) work as a catalyst to activate PAA with the generation of ROS dominated by CH3CO2• and CH3CO3• in the period of 0–10 min; 2) boost the production of iron ions by accelerating the corrosion of mZVI in the following 10–30 min, in which •OH played a main role in contaminant degradation. The eight intermediate degradation products of SMX resulted from the attack of •OH, CH3CO2• and CH3CO3• were detected and the possible degradation pathways were proposed. The biological acute toxicity of the Co@mZVI system during the treatment of SMX decreased over the reaction time. Additionally, Co@mZVI has good recovery ability and stability, suggesting the potential applicability of the Co@mZVI/PAA system in degrading antibiotics.

Study of synergistic effect of cobalt and carbon codoped with TiO2 photocatalyst for visible light induced degradation of phenol

In this work, we reported synthesis of cobalt and carbon codoped TiO2 (Co–C–TiO2) nanoparticles were prepared using co-precipitation technique. The synthesized catalysts are analyzed by various methods. The powder XRD pattern confirmed that all the samples were polycrystalline of anatase phase and particle size of resultant nanoparticle was reduced correlated with bare TiO2 sample. FTIR measurements exhibit the identification of functional groups present at the surface of TiO2. FESEM micrograph showed that the shape of codoped TiO2 nanoparticles are approximately sphere. The attained energy gap of Co doped and C codoping of TiO2 modifies to a level below the energy gap of TiO2 anatase specifying a high capability to absorb visible light. The recombination rate of photo-induced electrons and holes for Co–C codoped TiO2 nanoparticles is significantly reduced. The synthesized samples are assessed in degradation of phenol by the illumination of visible light. The results confirmed that photocatalytic activity enhanced due to doping and codoping of Co and C. As a result, Co–C codoped TiO2 nanoparticles exhibited a higher visible-light photocatalytic activity in compared with Co–TiO2 and bare TiO2 with the maximum degradation efficiency of 98, 75 and 15%, respectively. And also, the reusability of the catalyst was proved when 95% degradation could be achieved after consecutive batches. It is predictable that this work will provide new insights to increase the visible light active photocatalysts for environmental problems.

Cobalt and titanium co-doped zinc ferrite film photoanode with boosted interfacial photoelectrocatalytic activity for efficient degradation of tetracycline via the covalency competition in the Zn-O-Fe backbone

• The co-doping of Co and Ti in the ZFO leads to its lattice expansion. • LB-CoTiZFO film shows higher PEC activities than LB-ZFO film in TC degradation. • Surface rearrangement occurs in the LB-CoTiZFO film under the PEC circumstances. • Fe-O bond breakage caused by the covalency competition leads to boosted PEC activity. For efficient removal of the residual tetracycline (TC) in the aquatic environment, a novel cobalt (Co) and titanium (Ti) co-doped zinc ferrite (CoTiZFO) film was prepared via the Langmuir-Blodgett (LB) method in this study. With the co-doping of Co and Ti, the interfacial photoelectrocatalytic (PEC) activities for degradation of TC by the LB-assembled CoTiZFO (LB-CoTiZFO) films were significantly improved. As the applied voltage was 0.6 V in a two-electrode system, the five-layered LB-CoTiZFO (LB-CoTiZFO-5) films exhibited the optimal TC degradation rate and mineralization rate, which were accordingly 92.85% ± 1.45% and 81.92% ± 0.26%. In the same case, the kinetic rate constant ( k ) for PEC degradation of TC by the LB-CoTiZFO-5 films is equivalent to 3.3-fold of that by the films without the co-doping of Co and Ti. Under the PEC circumstances, the Co 3+ and Ti 4+ in the LB-CoTiZFO-5 film would be reduced to Co 2+ and Ti 3+ , while the Fe 2+ was oxidized to Fe 3+ , which results in the surface rearrangement of the LB-CoTiZFO-5 film. In addition, the Density Functional Theory (DFT) calculation results manifest the covalency competition in the Zn-O-Fe backbone can lead to the Fe-O bond breakage, the bare Fe metals with unpaired valence electrons will diffuse to the Helmholtz layer and serve as active sites, which endows the LB-CoTiZFO-5 films with boosted interfacial PEC activities. Therefore, the LB-CoTiZFO-5 film photoanode shows great prospective in efficient PEC degradation of TC.

Enhanced Catalytic Performance of FeCoNi/N-Doped Carbon Nanospheres as Bifunctional Oxygen Catalysts

Iron, cobalt, nickel, and nitrogen doped-carbon nanospheres (FeCoNi/N-C) are synthesized by the pyrolysis of globular Fe/Co/Ni-polypyrrole formed through a microemulsion method. The content and ratio of Fe/Co/Ni in N-C can be adjusted by adding different quantities of metal ions in microemulsion. Compared to Fe/N-C, FeCoNi/N-C demonstrates high conductivity, fast mass transport, superior catalytic properties of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The results showed multi-doping can facilitate the combination of metal and nitrogen and sustain their contents in pyrolysis process to improve conductivity and enhance bifunctional activities. According to the density functional theory calculations, co-doping of Co or/and Ni with Fe element on N-C material can help the desorption of *OH into water in ORR and accelerate the transformation of *O to *OOH in OER. Besides, FeCoNiN4 is a dominant contributor to bifunctional activities.

Degradation of tetrabromobisphenol A through peroxymonaosulfate oxidation activated by La0.5Sr0.5CoxMn1-xO3-δ perovskite.

La0.5Sr0.5CoxMn1-xO3-δ (LSCM) perovskite composite oxides prepared by co-doping of Co and Mn in B site-activated peroxymonosulfate (PMS) to degrade tetrabromobisphenol A. The characterization results indicated that the LSCM with x=0.3-0.8 have hexagonal R-3c structure. The activation effect of LSCM on PMS decreased gradually with the increase of Mn doping, among which LSCM82 (x=0.8) had good oxygen desorption performance certificated by O2-TPD and lower relative acidity (1.975). Moreover, the redox pairs of Co/Mn multi-valence ions were the main contributor to its catalytic activity. The electron spin resonance results suggested that SO4•- and •OH existed in the system and SO4•- is the main free radical. Therefore, LSCM82 perovskite catalyst has broad application prospects in aqueous solutions.

Ethylene glycol assisted three-dimensional floral evolution of BiFeO3-based nanostructures with effective magneto-electric response.

Controlled growth of nanostructures plays a vital role in tuning the physical and chemical properties of functional materials for advanced energy and memory storage devices. Herein, we synthesized hierarchical micro-sized flowers, built by the self-assembly of highly crystalline, two-dimensional nanoplates of Co- and Ni-doped BiFeO3, using a simple ethylene glycol-mediated solvothermal method. Pure BiFeO3 attained scattered one-dimensional nanorods-type morphology having diameter nearly 60 nm. Co-doping of Co and Ni at Fe-site in BiFeO3 does not destabilize the morphology; rather it generates three-dimensional floral patterns of self-assembled nanoplates. Unsaturated polarization loops obtained for BiFeO3 confirmed the leakage behaviour of these rhombohedrally distorted cubic perovskites. These loops were then used to determine the energy density of the BiFeO3 perovskites. Enhanced ferromagnetic behaviour with high coercivity and remanence was observed for these nanoplates. A detailed discussion about the origin of ferromagnetic behaviour based on Goodenough–Kanamori's rule is also a part of this paper. Impedance spectroscopy revealed a true Warburg capacitive behaviour of the synthesized nanoplates. High magneto-electric (ME) coefficient of 27 mV cm−1 Oe−1 at a bias field of −0.2 Oe was observed which confirmed the existence of ME coupling in these nanoplates.

The effect of Co and Ce codoping in CuIn0.9CexCo0.1−xTe2

The codoped dilute magnetic semiconductor CuIn0.9CexCo0.1−xTe2 has been successfully prepared by arc melting and vacuum solid-state reaction technologies. CuIn0.9CexCo0.1−xTe2 crystallizes into body centered tetragonal structure with a space group of I4¯2d. The codoping of Co and Ce induces the room temperature ferromagnetism in CuIn0.9CexCo0.1−xTe2. The magnetization of CuIn0.9CexCo0.1−xTe2 are enhanced by codoping Ce and Co into CuInTe2, which is ascribed to the exchanging interaction between 4f electron of Ce and 3d electron of Co. Magnetic measurements show that Co influences mainly on the saturation magnetic moment of CuIn0.9CexCo0.1−xTe2. The high doping ratio of Co and Ce is beneficial for increasing saturation magnetization and the magnetic transformation temperature. Codoping Ce and Co into CuInTe2 can adjust the light absorption bandgap from 0.92 eV to 1.08 eV, which is slightly higher than that of CuInTe2. It shows that the light absorption bandgap can be refined by controlling Co/Ce ratio for the potential application of solar cell material.

The effect of Sn codoping on the local Co structural environments of (In0.95-xSnxCo0.05)2O3 thin films using x-ray absorption spectroscopy

The effect of Sn codoping on the local Co structural environments of the (In0.95-xSnxCo0.05)2O3 (x = 0, 0.02, 0.05, 0.08) films has been investigated in detail by x-ray absorption spectroscopy at Co K-edge and L-edge. The results show that the Sn codoping can remarkably influence the local Co structures of the films. For the films with low Sn concentration (x ≤ 0.02), most Co2+ atoms substitute for In3+ sites of In2O3 lattices, while a part of Co atoms form the precipitate of Co metal clusters. With further increasing Sn concentration (x > 0.02), the doped Co atoms are completely substitutionally incorporated into the In2O3 lattices. It can be concluded that the codoping of Co and Sn atoms forms p-n pairs of electronics and holes with opposite charge state, which can activate the substitution of Co atoms in In2O3 lattice and suppress the forming of metallic Co clusters. The p-n codoping method can provide a powerful guiding principle in designing the oxides based diluted magnetic semiconductors.

Study on the ferromagnetism in Co and N doped ZnO thin films

Present investigation reports the structural, optical and magnetic properties of co-doping of Co and N ions in ZnO samples, prepared by two distinct methods. In the first method, samples are synthesized by Sol–gel technique in which the Co and N are co-doped simultaneously during the growth process itself. In the second case, N ions are implanted in the Co doped ZnO thin films grown by Pulsed Laser Deposition (PLD). Structural studies showed that the nitrogen implantation on Co doped ZnO samples developed compressive stress in the films. X-ray photoelectron spectroscopy confirmed the doping of Co and N in ZnO matrix. In the Resonant Raman scattering multiple LO phonons up to fifth order are observed in the (Co, N) co-doped ZnO. Photoluminescence spectra showed that there is reduction in the bandgap due to the presence of Co in the lattice and also the presence of Zn vacancies in the films. All samples showed ferromagnetic behavior at room temperature. The magnetic moment observed in the implanted films is found to be varied with the different dosages of the implanted N ions. First principle calculations have been carried out to study the possible magnetic interaction in the co-doped system. Present study shows that the ferromagnetic interaction is due to the hybridization between N 2p and Co 3d states in the (Co, N) co-doped ZnO and is very sensitive to the geometrical configurations of dopants and the vacancy in the ZnO host lattice.

Thermoelectric Properties of P-Type Heusler Compounds (Fe<SUB>2−<I>x</I></SUB>Co<I><SUB>x</SUB></I>)(V<SUB>1−<I>y</I></SUB>Ti<I><SUB>y</SUB></I>)Al

We report on the effect of Co and Ti co-doping on the thermoelectric behavior of Fe 2 VAl based alloys. The doped alloys, (Fe 2-x Co x )(V 1-y Ti y )Al, with compositions x = 0.01-0.07 and y = 0.04-0.20 exhibit a p-type thermoelectric property when the total valence electron number is below 24. The co-doping of cobalt and titanium is believed to cause a substantial shift of the Fermi level from the center of the pseuodgap to a lower energy position. In particular, the alloy with x = 0.03 and y = 0.10 exhibits a p-type thermoelectric behavior with a large Seebeck coefficient of S = 85 μV/K as well as a low electrical resistivity of p = 2.3 μ Ωm at 400 K, so that the power factor, P = S 2 /p, reaches 3.2 x 10 -3 W/m K 2 . The power factor is larger than that of the Ti doped Fe 2 VAl alloy so far reported. The high power factor caused by the co-doping of Co and Ti might be due to a modification in the band structure on the valence band side around the Fermi level. The co-doping of Co and Ti is also effective in reducing the thermal conductivity, mainly due to phonon scattering.