(1). The stabilization of these dissolved strong oxidizing agents varies with the alkali metal: sodium hydroxide stabilizes the peroxide species (reaction (2)), while potassium hydroxide stabilizes both peroxide and superoxide (reactions (2) and (3)). For this reason, the KOH-based hydroflux promotes a more oxidizing environment than the NaOH-based hydroflux and favors a Mn(V) phase, contrary to the NaOH system. This explains the phase speciation between Sr5(Mn V O4)3OH and SrMn IV O3 in the q(H2O)A ≥ 2.2 and q(Sr) = 1 region. Furthermore, increased oxidation power is consistent with the fact that pentavalent manganese is present in all major phases obtained from KOH-based hydrofluxes, contrary to the NaOH-based ones, where the main products involve tetravalent manganese for some initial compositions (Figure ).