Vibrational spectroscopic study of the site occupancy distribution of cations in nickel cobalt oxides

Abstract

Mid-infrared, far-infrared, and Raman spectra for Ni1−xCoxOy indicated the systematic variation from a spinel-type (x=1.0) to an inverse spinel-type (x=0.67) lattice, through a multiphase transition region, to an NaCl-type (x<0.25) structure. Further analysis reveals that a decrease in x in this system is accompanied by the formation of octahedral/Ni2+, which, in the case of spinel compositions Ni1−xCoxO4/3 (x=0.67 to 1.0), results in substitution of Co3+ into tetrahedral sites and/or the redistribution of charge around some of the oxygen ions. The proposed transition region explains the observed break in continuity, at around x=0.5, in the previously reported resistivity data for nickel cobalt oxide films.

Atomic layer deposition of nickel–cobalt spinel thin films

“…This is similar to the observations which Windisch et al 44 replacement of Co 3+ by Ni 2+ ions and the decrease in peak intensity and increase of bandwidth with the related decrease of symmetry at the O h site. 44 In order to demonstrate the presence of weak Raman peaks in the stoichiometric (Co 1−x Ni x ) 3 O 4 films with x=0.33, an inset with the Raman spectrum of a thicker film (∼ 192 nm) is included in Figure 5. Iliev et al 42 also observed weak and broad peaks for their metallic films grown at low temperatures but obtained sharp peaks for their insulating films grown at high temperatures during their epitaxy studies supporting the idea that ionic disorder is responsible for the low resistivity.…”

“…Bitla et al 19 who investigated similar films (epitaxial, on MgAl 2 O 4 ) carried out extensive investigations of the cation distribution by X-ray absorption spectroscopy (XAS) and obtained (Co 43 Another F 2g would be expected at about 522 cm −1 but cannot be identified here due to the interference with a signal from Si. When Ni is added, the intensity of the peaks decreases dramatically, its width increases and the A 1g peak that is usually assumed to be dominated by the O h oxygen atoms 44 shifts to lower wavenumbers. This is similar to the observations which Windisch et al 44 replacement of Co 3+ by Ni 2+ ions and the decrease in peak intensity and increase of bandwidth with the related decrease of symmetry at the O h site.…”

“…When Ni is added, the intensity of the peaks decreases dramatically, its width increases and the A 1g peak that is usually assumed to be dominated by the O h oxygen atoms 44 shifts to lower wavenumbers. This is similar to the observations which Windisch et al 44 replacement of Co 3+ by Ni 2+ ions and the decrease in peak intensity and increase of bandwidth with the related decrease of symmetry at the O h site. 44 In order to demonstrate the presence of weak Raman peaks in the stoichiometric (Co 1−x Ni x ) 3 O 4 films with x=0.33, an inset with the Raman spectrum of a thicker film (∼ 192 nm) is included in Figure 5.…”

Synergistic electrocatalytic activity of a spinel ZnCo2O4/reduced graphene oxide hybrid towards oxygen reduction reaction

“…2a The Raman band at 658 cm −1 is a shoulder peak and it shows the same A 1g symmetry which also can be assigned to the peak at 682 cm −1 , and both the peaks arise due to the vibrational energy from stretching of Co-O bonds. All these peaks are characteristic peaks for a normal spinel like ZCO and other spinels that are more or less similar to ZCO [55][56][57][58][59]. The characteristic 'D' and 'G' bands at 1345 and 1585 cm −1 , respectively, clearly depict the presence of RGO [60].…”

Synthesis and gas sensor applications of nanostructured ZnO grown at low temperatures

“…It could be successfully explained in terms of resonant anharmonic interaction of the high-E 2 mode with a band of combined transverse and longitudinal acoustic modes, as the steep variation of the 2-phonon density of states around the high-E 2 frequency leads to a distorted phonon line shape. One can suggest that mixing 2 different cations through doping in aqueous solution could affect the local polarizability by charge distribution and result in at least 1 vibrational mode being strongly influenced [6,19,20].…”