Theoretical investigation of the inversion parameter in Co3−sAlsO4 (s=0–3) spinel structures

The effect of annealing temperature on the structure and optical properties of sol–gel derived nanocrystalline cobalt aluminate spinel

“…The samples were prepared by the solegel technique using aluminum-sec-butoxide [Al(O s Bu) 3 ] and cobalt nitrate hexahydrate Co(NO 3 ) 2 Â 6H 2 O as starting materials and ethyl-acetoacetate (C 6 H 10 O 3 ) as a chelating agent. The powder precursors were annealed at various temperatures ranging from 200 to 900 C. The properties of products were characterized using differential thermal analysis and thermogravimetric analysis (DTA/TGA), UVevis diffuse reflectance spectroscopy (DRS) and X-ray diffraction (XRD).…”

“…Generally, cobalt compounds range in color from pink to green and blue depending on the host lattice, oxidation state and coordination site of the cobalt ion. The occurrence of the green color is associated with electronic transitions of the Co 3þ in octahedral coordination [3,4]. Compounds in which cobalt has an oxidation state þ2 and the ions situated in the octahedral position are pink to violet in color [5].…”

“…Compounds in which cobalt has an oxidation state þ2 and the ions situated in the octahedral position are pink to violet in color [5]. On the other hand, compounds in which Co 2þ is placed in tetrahedral coordination are intensively blue due to the electronic transitions of Co 2þ in tetrahedral coordination [3]. One of the most common crystalline structures used as a host for the cobalt ion is the spinel structure, and one of most common compounds used for this purpose is the cobalt aluminate (CoAl 2 O 4 ).…”

Evolution of structural and optical properties in the course of thermal evolution of sol–gel derived cobalt-doped gahnite

“…The occurrence of an intense blue color is not a surprise because many common cobalt pigments, cobalt aluminate being one of them, are intense blue due to electronic transitions of Co 2+ in tetrahedral coordination [11]. On the other hand, the occurrence of green color is associated with electronic transitions of Co 3+ in octahedral coordination [11], i.e.…”

“…On the other hand, the occurrence of green color is associated with electronic transitions of Co 3+ in octahedral coordination [11], i.e. it points out to a partial oxidation of Co 2+ to Co 3+ species [10].…”