Spectroscopic studies of Co₂TiO₄ and Co₃O₄ two‐phase composites

Abstract

In this article, we report a comparative analysis of various spectroscopic studies including low‐temperature (25thinmathspacenormalKthinmathspace≤T≤300normalK) Raman spectroscopy of cobalt‐orthotitanate (Co2TiO4) and tricobalt‐tetraoxide (Co3O4), and their solid solutions false(1−xfalse) Co3O4+x of Co2TiO4 (0≤x≤1 (100 wt.%)). For all the lower and intermediate compositions, five Raman‐active modes were recognized at 689, 618, 518, 480, and 195cm−1 that are associated with A1g, Eg, and 3F2g phonon symmetries. Conversely, pure Co2TiO4 exhibits a broad spectrum of width ∼93.3cm−1 without any signatures of F2g(3) mode. At low‐temperatures (down to 25 K) the A1g and F2g peaks of both Co2TiO4 and Co3O4 shift toward the high‐frequency side with anomalies across the ferrimagnetic Néel temperature (TN ∼48±5K) and antiferromagnetic Néel temperature (TN∼ 30 ± 10 K), respectively. All the investigated samples exhibit two distinct bands at 576cm−1 (B1) and 665cm−1 (B2) in the Fourier transform infrared spectra recorded at 300±10 K, associated with the vibrational stretching of the metal–oxygen bonds of length ∼195.8 pm (B–O) and ∼185.4 pm (A–O), respectively. The intensity of these sharp bands gradually decreases as the crystal structure transforms from normal‐spinel (a=8.07 Å) to inverse‐spinel structure (a=8.45 Å). The X‐ray photoelectron spectroscopy (XPS) studies revealed that the Ti was incorporated into the octahedral B‐sites of inverse‐spinel structure of Co2TiO4. Interestingly, the XPS spectra of Co2TiO4 provide evidence of the trivalent character of Ti instead of tetravalent cationic configuration together with a weak Co3+ character at the octahedral sites. These results are discussed in terms of the binding‐energy (BE) difference between the O‐1s and Ti‐2p3/2 (Δ[O–Ti‐2p3/2] = BE(O‐1s) −BE(Ti‐2p3/2false)) and the mean chemical bond length lfalse[italicTi−Ofalse]. The peculiarities of all these results in consonance with the crystal‐structure (bond angles and bond lengths) and electron‐spin‐resonance studies are discussed in detail.

Co2TiO4/Reduced Graphene Oxide Nanohybrids for Electrochemical Sensing Applications

“…The symmetric character of the Ti 2p spectral lines recorded from the materials prepared in this work ruled out the presence of a Ti 3+ contribution. In conclusion, our low temperature method produced a CTO with only Ti 4+ , in contrast with results recently reported for CTO prepared by a high-temperature solid-state reaction, where Ti presented a trivalent character in this compound [64].…”

“…These binding energy values and the occurrence of the intense satellite features were fully compatible with the presence of Co 2+ [63]. Although the fairly intense satellites suggested that the materials exclusively contained Co 2+ , we explored the possible existence of a Co 3+ contribution, which had been recently observed elsewhere [64]. It is known that oxides with spinel-related structures contain Co 3+ that can be characterized by a spin–orbit doublet with a binding energy of the main Co 2p 3/2 core level of 779.6 eV [63].…”

Spectroscopic characterization of commercial pigments for pictorial retouching

“…From this point of view, the quite sharp feature at about 548 cm −1 could be related to the F 2g mode, documented to shift toward longer wavenumbers when Ti is introduced in the cobalt oxide octahedral site increasing the bond length between the central cation and the oxygen atoms. [ 35 ] The presence of additional elements can further modify the band position. The same applies to the 468 cm −1 band.…”

“…Caggiani et al [19] Ruiz-Preciado et al [33] Jiang et al [34] 346, 601 Caggiani et al [19] Nayak et al [35] Casadio et al [36] 705 A g -symmetric stretching of CoO Other studies [19,33,[35][36][37] Barite (BaSO…”

Study of Filament Resistive Switching in New Pt/Co0.2TiO3.2/ITO Devices for Application in Non‐Volatile Memory

“…In order to clarify that the assumption of oxygen vacancies is possible that the existence of the resistive switching devices, perform Raman spectroscopy measures the CTO target used in the sputtering deposition, highlighted in Figure . From the Raman spectrum we were able to observe six modes of phonons in 158 (F 2g ), 255 (E g ), 345 [T 2g (1)], 460 [T 2g (2)], 615 (A 1g ) e 701 (A 1g ) cm −1 , their respective assignments can be identified in the references . In particular to the A 1g ≈615 cm −1 mode, a widening that is attributed to intrinsic oxygen vacancies (represented in the deconvolution), which can be manifested by the coexistence of Co 3+ and Co 2+ ions, or also evidenced when in the structure inverse spinel (Co 2+ [Co 3+ Ti 4+ ]O 4 ) occupations of the octahedral sites of Ti 4+ by Co 3+ occurring with oxygen vacancies for local stabilization of charge .…”