Potassium-conducting solid electrolytes in the systems K2 ? 2xAl2 ? xMxO4 (M = Nb, Ta)

New potassium-monoaluminate-based solid electrolytes with high potassium-cationic conductance are synthesized, by partial substitution of penta-charged cations Nb⁵⁺ and Ta⁵⁺ for Al³⁺ cations, and studied. Both additives increased drastically the KAlO₂ conductivity over the entire studied temperature range. The reason for the increase in the potassium monoaluminate conductivity, on the introducing of the studied additives, is the formation of potassium vacancies as a result of the substitution reaction Al³⁺ → Nb⁵⁺(Ta⁵⁺) + 2V’c, as well as broadening of the region of existence of the KAlO₂ high-temperature γ-modification whose transport properties exceed those of the low-temperature β-form.