Parallel migration of potassium and oxygen ions in hexagonal tungsten bronze - Bulk diffusion, surface segregation and desorption

in the synthesized materials were investigated by means of ionic conductivity (bulk diffusion), work function and soot oxidation (surface segregation) and potassium thermal desorption studies. The energetic barrier for potassium bulk diffusion (1.2 eV) and desorption (4.4 eV), as well as the corresponding characteristic temperature of their onsets ~ 450 °C and ~ 500 °C were determined. The results are discussed in terms of a simple proposed model of potassium and oxygen migration in K0.3WO3 coupled with changes of the tungsten oxidation state. It was revealed that the structure of potassium tungsten bronze is preserved in an inert atmosphere in a wide temperature range of 400-700 °C, regardless the migration processes. This specific feature of the K0.3WO3 phase predisposes its possible application as an alkali reservoir in composite catalysts for processes where the coking appears.