Synthesis and structural characterization of CaMg0.5CoxNi0.5-xSi2O6 (0 ≤ x ≤ 0.5) solid solutions as a colouring substance

Abstract

In this study, CaMg0.5CoxNi0.5-xSi2O6 (0.0 ≤ x ≤ 0.5) solid solutions with a diopside structure were prepared to reduce the cobalt and nickel amounts compared to M2SiO4 or MgMSiO4 (M = Co, Ni) compounds or CaCoxNi1-xSi2O6 solid solutions. Colloidal gels were obtained by adding an ammonia aqueous solution to the suspensions of precursors in aqua until pH = 10. Diopside structure began to develop at 800 °C and at 1000–1200 °C crystallinity and pink colour of materials (x ≠ 0) are optimal. In both CaMg0.5CoxNi0.5-xSi2O6 (0.0 ≤ x ≤ 0.5) and MgCoxNi1-xSiO4 (0.0 ≤ x ≤ 1.0) solid solutions with diopside and olivine structures the position of the third transition of octahedral Co(II), 4T1 → 4T1(P), is centred into the green absorption range and the observed colour is pink. A higher red amount in diopside than in olivine structure can be explained by the minor width of band of this third transition (minor distortion of octahedral M1 site) and shorter mean M1-O distances (M = Ni, Co).