Spectroscopic studies of Co2TiO4 and Co3O4 two‐phase composites. Issue 11 (14th September 2016)

• Record Type: Journal Article
• Authors: Nayak, S.; Dasari, K.; Joshi, D. C.; Pramanik, P.; Palai, R.; Sathe, V.; Chauhan, R. N.; Tiwari, N.; Thota, S.
• Is Part Of: Physica status solidi. Volume 253:Issue 11(2016)
• Page Start: 2270
• Page End: 2282
• Publication Date: 2016-09-14
• Subjects: antiferromagnetism -- Co3O4 -- Co2TiO4 -- Raman spectroscopy -- Solid solutions -- spinels -- vibrational modes; Solid state physics -- Periodicals; Solids -- Periodicals; Atomic structure -- Periodicals; 530.41
• DOI: 10.1002/pssb.201600295
• Languages: English
• ISSNs: 0370-1972

Abstract

Abstract: In this article, we report a comparative analysis of various spectroscopic studies including low‐temperature ( 25 K ≤ T ≤ 300 K ) Raman spectroscopy of cobalt‐orthotitanate ( Co 2 TiO 4 ) and tricobalt‐tetraoxide ( Co 3 O 4 ), and their solid solutions ( 1 − x ) Co 3 O 4 + x of Co 2 TiO 4 ( 0 ≤ x ≤ 1 (100 wt.%)). For all the lower and intermediate compositions, five Raman‐active modes were recognized at 689, 618, 518, 480, and 195 cm − 1 that are associated with A 1 g, E g, and 3 F 2 g phonon symmetries. Conversely, pure Co 2 TiO 4 exhibits a broad spectrum of width ∼ 93.3 cm − 1 without any signatures of F 2 g (3) mode. At low‐temperatures (down to 25 K) the A 1 g and F 2 g peaks of both Co 2 TiO 4 and Co 3 O 4 shift toward the high‐frequency side with anomalies across the ferrimagnetic Néel temperature ( T N ∼ 48 ± 5 K) and antiferromagnetic Néel temperature ( T N ∼ 30 ± 10 K), respectively. All the investigated samples exhibit two distinct bands at 576 cm − 1 ( B 1 ) and 665 cm − 1 ( B 2 ) 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 Co 2 TiO 4 . Interestingly, the XPS spectra of Co 2 TiO 4 provide evidence of the trivalent character of Ti instead of tetravalent cationic configuration together with a weak Co 3 + 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 3 / 2 ( Δ [O–Ti‐2 p 3 / 2 ] = BE(O‐1 s ) −BE(Ti‐2 p 3 / 2 ) ) and the mean chemical bond length l [ Ti − O ] . 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.