Spectroscopic studies of Co₂TiO₄ and Co₃O₄ two‐phase composites

Abstract

Abstract In this article, we report a comparative analysis of various spectroscopic studies including low‐temperature ( ) Raman spectroscopy of cobalt‐orthotitanate ( ) and tricobalt‐tetraoxide ( ), and their solid solutions of ( (100 wt.%)). For all the lower and intermediate compositions, five Raman‐active modes were recognized at , and that are associated with , , and phonon symmetries. Conversely, pure exhibits a broad spectrum of width without any signatures of (3) mode. At low‐temperatures (down to 25 K) the and peaks of both and shift toward the high‐frequency side with anomalies across the ferrimagnetic Néel temperature ( K) and antiferromagnetic Néel temperature ( K), respectively. All the investigated samples exhibit two distinct bands at 576 ( ) and 665 ( ) in the Fourier transform infrared spectra recorded at 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 ( Å) to inverse‐spinel structure ( Å). The X‐ray photoelectron spectroscopy (XPS) studies revealed that the Ti was incorporated into the octahedral B‐sites of inverse‐spinel structure of . Interestingly, the XPS spectra of provide evidence of the trivalent character of Ti instead of tetravalent cationic configuration together with a weak character at the octahedral sites. These results are discussed in terms of the binding‐energy (BE) difference between the O‐1 s and Ti‐2 p ( [O–Ti‐2 p ] = BE(O‐1 s ) −BE(Ti‐2 p ) and the mean chemical bond length . 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.