Growth and electrical properties of pure and Ni-doped Co3O4 single crystals

doi:10.1016/0025-5408(84)90212-5

Materials Research Bulletin

Volume 19, Issue 8, August 1984, Pages 989-997

https://doi.org/10.1016/0025-5408(84)90212-5 Get rights and content

Abstract

Single crystals of pure and Ni-doped Co₃O₄ spinel-type phases have been grown by C.V.T. Electrical conductivity and thermopower measurements have been performed between 25 and 950 K. Ni-doping gives rise to a significant increase of electrical conductivity at room temperature by three orders of magnitude. The obtained results suggest that the Ni atoms are located in the octahedral sites of the spinel lattice with both oxidation states 2+ and 3+, as illustrated by the formula : Co²⁺_1−yCo³⁺_y[Co³⁺_2−xNi²⁺_yNi³⁺_x−y]O₄.

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Temperature-induced structural phase transformation in samples of Co<inf>3</inf>O<inf>4</inf> and Co<inf>3-x</inf>Ni<inf>x</inf>O<inf>4</inf> for CoO
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Citation Excerpt :
Specifically, in relation to the sudden non-linear increase in the lattice parameter that indicates a structural abnormality at high temperature. Depending on the temperature ranges used, the insertion of a dopant plays an important role in increasing conductivity, as well as in the evolution of activation energy [56]. The values of the main Rietveld refinement parameters are presented in Table 5.
Undoped and Ni-doped cobalt oxide (Ni=4%) powders were prepared by hydrothermal synthesis and subsequently examined. The powders obtained were subjected to thermal annealing at temperatures ranging between 600 °C and 1000 °C. The experimental results indicate that the annealing affects the structural properties with the phase change Co₃O₄ to CoO. X-Ray diffraction (XRD) analysis reveals the presence of pure spinel phase up to 800 °C in powders obtained with and without the addition of nickel. From 900 °C, the CoO phase was observed. Rietveld refinement was conducted with main GOF values between 1.09 and 1.26 and also x₂ values between 1.28 and 1.57, indicating a good correspondence between the simulated and the experimental pattern. In addition, SEM measurements evidenced that particle size increased with temperature; however, samples doped with Ni exhibited a slightly smaller size compared to pure samples. The synthesized powders showed shifted and broad bands Raman, with increasing temperature, mainly for doped samples. These changes in the position of Raman vibrational modes are related to defects and distortions in the crystal lattice of the material as a result of the increase in temperature and the addition of Ni. Furthermore, such changes may also indicate loss of crystallinity in the material, or the beginning of the phase change.
Outstanding stability and photoelectrochemical catalytic performance of (Fe, Ni) co-doped Co<inf>3</inf>O<inf>4</inf> photoelectrodes for solar hydrogen production
2021, International Journal of Hydrogen Energy
In this work, pure and (Fe, Ni) co-doped Co₃O₄ nanostructured photoelectrodes of different doping levels and thicknesses were manufactured at constant substrate temperature (450 °C) using the spray pyrolysis technique. In addition to the chemical compositions; the structural, optical, electrical, and photoelectrochemical (PEC) properties were investigated through the use of various analysis techniques. By increasing the codpoing ratio to 6%, the low energy band gap is decreased from 1.43 to 1.3 eV and the high energy bandgap is increased from 2.63 to 2.87 eV, in addition to the reduction in particle size from 30.2 to 12.0 nm. The high energy gap vanishes by increasing the codoped film's spread volume to 60 ml. X-ray photoelectron spectroscopy of 6%(Fe, Ni)-60ml Co₃O₄ confirms the existence of Ni^2+,3+ and Fe^2+,3+. Among the studied photoelectrodes, the 6%(Fe, Ni)-60ml Co₃O₄ photoelectrode displays a photocatalytic hydrogen output rate of 150 mmol/h.cm² @-1V in 0.3M Na₂SO₄ electrolyte. The photocurrent density of 6%(Fe, Ni)-60ml photoelectrode reached up to 13.6 mA/cm²@-1V with an IPCE (incident photon to current conversion efficiency) of ∼42%@405 nm and STH (solar to hydrogen conversion efficiency) of ∼11.37%, which are the highest values yet for Co₃O₄-based photocatalysts. The value of ABPE(applied bias photon-to-current efficiency) is 0.34%@(-0.28V and 636 nm). Interestingly, this photoelectrode shows a photogenerated current density of −0.14 mAcm⁻² at 0 V and a PEC current onset over 0.266V. The thermodynamic parameters, corrosion parameters, PEC surface areas, Tafel slopes, and impedance spectroscopies are also being studied to confirm and classify the PEC H₂ production mechanism. The 6%(Fe, Ni)-60ml Co₃O₄ photoelectrode stability/reusability shows only a 6.6% reduction in PEC performance after ten successive runs at -1V with a corrosion rate of 1.2 nm/year. This work offered a new codoping strategy for the design of a highly active Co₃O₄ based photocatalyst for the generation of solar light-driven hydrogen.
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2019, Ceramics International
Bismuth Cobalt Oxide (Bi_xCo_3-xO₄) nanoparticles with different compositions (x = 0, 0.025, 0.05, 0.1, 0.2) were prepared by chemical precipitation method. The structural, morphological and thermal properties of the prepared samples were studied by XRD, SEM, FTIR and TG&DTA analysis. X-ray diffraction analysis shows that pure phase of Cobalt oxide was formed till x ≤ 0.05 and while increasing the Bi concentration (0.05 ≤ x ≤ 0.2) mixed phases of Co₃O₄, Co₂O₃, CoO and separate phase of Bi₂O₃ were formed. The diffraction peaks were reasonably shifted due to substitution of Bi²⁺ ions. XPS analysis conforms the presence of mixed valance states of Co and presence of Bi with their binding states in the samples. The electrical resistivity and Seebeck coefficient were measured for Bi_xCo_3-xO₄ (0 ≤ x ≤ 0.2) at different temperatures. It was observed that the electrical resistivity decrease till x ≤ 0.05 due to the substitution of Bi ions in Cobalt lattice and increases at higher x values (0.05 ≤ x ≤ 0.2) due to the formation of Bi₂O₃ phase. The Bi substitution has considerably reduced the electrical resistivity by one order when completely dissolved in the cobalt oxide lattice at lower x values. The Seebeck coefficient value gradually increased for all samples of Bi_xCo_3-xO₄ (0 ≤ x ≤ 0.2). The power factor was calculated from electrical resistivity and Seebeck coefficient and the maximum power factor of 0.025 µWm⁻¹K⁻² was obtained for Bi_0.2Co_2.8O₄ sample at 530 K. The experimental results revealed that the Bi substitution have promising effect on the thermoelectric properties of nanostructured Bi_xCo_3-xO₄ (0 ≤ x ≤ 0.2).

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^∗: Permanent address: Mineralogical Institute, Mysore University, Mysore, 570 006, India

^∗∗: Permanent address: School of Mining and Metallurgy, Institute of Material Science, 30-059 Cracow, Al. Mickiewieza 30, Poland.

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Growth and electrical properties of pure and Ni-doped Co3O4 single crystals

Abstract

J. Inorg. Nucl. Chem.

Comm. Dept. Chem. Bulg. Acad. Sci.

Comm. Dept. Chem. Bulg. Acad. Sci.

J. Phys. Chem. Solids

J. Phys. Chem. Solids

J. Solid State Chem.

J. Phys. Soc. Jap.

J. Chem. Phys.

Growth and electrical properties of pure and Ni-doped Co₃O₄ single crystals