Effect of the interaction between basicity and reductive character of melting atmosphere – both extreme – on the oxidation and coordination states assumed by transition metals when doped to silicate glasses

The influence of an extremely reductive melting atmosphere on the oxidation and coordination states adopted by transition metals in an ultrabasic host was evaluated. An invert glass (46SiO₂·11Na₂O·21CaO·22BaO, basicity = 0.71) was synthesized in container-less conditions, on a jet of Ar−5%H₂. Performed measurements included optical absorption, optical emission and electron paramagnetic resonance spectroscopy. The results revealed that the used atmosphere dramatically decreases the oxidation state(s) dopants assume, compared to those stable under oxidative melting in such a host. After reductive melting: (i) Ti³⁺ appears alongside Ti⁴⁺; (ii) V³⁺ is added to V⁵⁺; (iii) Mn²⁺ fully substitutes Mn³⁺ and Mn⁵⁺; (iv) Cu²⁺ is entirely replaced by Cu⁺and Cu⁰. These results could be rationalized considering the action of additional factors like ligand-field stabilization energy, ionization energy and special filling numbers of the 3d-subshell. They modulate the interaction between basicity and atmosphere redox character, in a way specific to each transition metal.