SiO₂-Mediated Hydrothermal Synthesis of Spiroffite-Type Co₂Te₃O₈

The hydrothermal synthesis of novel materials typically relies on both knowledge of the redox activities of all cations present in the reaction solution and a small toolset of so-called mineralizers to tune the solution's overall chemical potential. Upon the use of a less conventional mineralizer species, SiO₂, we show the stabilization of spiroffite-type Co₂Te₃O₈ under less forceful hydrothermal conditions than those in previous reports. When synthesized in the presence of both SiO₂ and each respective alkali carbonate as a secondary mineralizer, silicon substitution in place of tellurium in the host structure becomes apparent, and the corresponding disorder introduced gives rise to enhanced low-temperature ferromagnetism. Our results highlight the complexities of underutilized and combined mineralizer species in the stabilization and tuning of complex magnetic ground states via hydrothermal synthesis techniques.