Off-Stoichiometric Nickel Cobaltite Nanoparticles: Thermal Stability, Magnetization, and Neutron Diffraction Studies

Abstract

In the present investigation, we report a detailed examination of the effect of off-stoichiometry introduced in NiCo 2 O 4 by adding excess cobalt. Thus, we compare and analyze the structural and magnetic properties of the Ni 0.75 Co 2.25 O 4 and NiCo 2 O 4 cubic systems. A low temperature combustion method was utilized to synthesize stoichiometric (NiCo 2 O 4 ) and off-stoichiometric (Ni 0.75 Co 2.25 O 4 ) nanoparticles on a large scale. The X-ray diffraction pattern for the sample annealed at high temperature (773 K) shows the presence of a much less intense NiO phase (∼2−5%) in Ni 0.75 Co 2.25 O 4 as compared to that in the case of NiCo 2 O 4 sample (∼15−20%). The Ni 2p and Co 2p XPS spectra reveal the coexistence of Ni 2+ , Ni 3+ , Co 2+ , and Co 3+ species on the surface of both the NiCo 2 O 4 and Ni 0.75 Co 2.25 O 4 samples in differing proportions. In addition to the basic magnetic characterizations using PPMS, these were also analyzed by neutron diffraction. The off-stoichiometric Ni 0.75 Co 2.25 O 4 sample shows an interesting magnetic phase conversion from frustrated dipolar system to an enhanced magnetic ordering upon annealing. Local moments on the lattice sites of NiCo 2 O 4 and Ni 0.75 Co 2.25 O 4 samples are further compared by neutron diffraction confirming stronger ordered moments and enhanced structural and thermal stability for the Ni 0.75 Co 2.25 O 4 sample.

Effect of Co/Ni ratios in cobalt nickel mixed oxide catalysts on methane combustion

“…Such an increment in the lattice parameter can be attributed to the insertion of Ni 2+ ions into octahedral sites in Co3O4 spinel structure because the ion radius of Ni 2+ (0.069 nm) is larger than that of Co 3+ (0.055 nm) [41]. Although the previous studies suggest that the diffraction peak may be shifted to lower angle owing to thermal decomposition of NiCo2O4 spinel phase, we exclude the possibility because calcination condition is fixed in this study [37,42].…”

One dimensionally spinel NiCo2O4 nanowire arrays: facile synthesis, water oxidation, and magnetic properties

“…As shown in Fig. S5, the T max of NiCo 2 O 4 is lower than the Co 3 O 4 , ascribed to the smaller crystalline size of NiCo 2 O 4 than the Co 3 O 4 , and the larger T max of NiO is attributed to its typical antiferromagnetic nature [41].…”

Nickel Cobaltite Nanostructures for Photoelectric and Catalytic Applications

“…Therefore, morphologically controllable synthetic methods aiming for well-defi ned nanocrystals are the primary step. So far, the main synthesis strategies include liquid-phase co-precipitation, [ 43,70 ] hydro-and solvothermal routes, [ 1,41,71 ] microwave-assisted methods, [ 72 ] electrodeposition methods, [ 32 ] electrospinning methods, [ 73 ] high-temperture [ 23,24,69 ] [ 30 ] mesoporous hollow sub-microspheres, [ 70 ] and hollow crossed nanocubes. [ 74 ] Microspheres ( Figure 2 a) and hollow sub-microspheres (Figure 2 b) (Figure 2d,e), [ 25,45 ] nanowires (Figure 2 f,g), [ 43 ] and nanotubes (Figure 2 h), [ 46 ] whose lateral dimensions are in the range of several hundred nanometers to several 2 Ti foil electrocatalytic oxygen evolution [11] nanowire arrays co-precipitation route Ni(NO 3 ) 2 , Co(NO 3 ) 2 − oxygen reduction reaction, electrocatalytic oxygen evolution [56] www.small-journal.com micrometers.…”

“…[ 68 ] Considering the thermal and structural instability of NiCo 2 O 4 phases at high temperature, the calcination treatment prevalent in high-temperature syntheses should be manipulated deliberately. [ 23 ] Verma and co-workers found a formation of NiO nanoparitcles owing to the partial decomposition of NiCo 2 O 4 above 673 K. [ 24 ] Cabo and co-workers also detected NiO impurities at 550 °C. [ 69 ] The calcination temperature will infl uence the hypostatic consititution and structure of nickel cobaltites directly.…”

“…[ 23 ] The magnetic properties and saturation magnetization of NiCo 2 O 4 can also be tuned by annealing, [ 24 ] morphology, [ 25 ] and components. [ 26 ] Iliev and co-workers have reported that epitaxial NiCo 2 O 4 fi lms deposited at temperatures lower than 450 °C are ferrimagnetic, and those grown at elevated temperatures are nonmagnetic.…”