Rubidium ion conducting Rb2-2x Al2-x A x O4 (A = Nb, Ta) solid electrolytes

Rb2 - 2x Al2 - x A (x) O-4 (A = Nb, Ta) solid solutions have been synthesized, and their conductivity has been measured as a function of temperature and composition. The highest rubidium ion conductivity in the Rb2 - 2x Al2 - x A (x) O-4 solid solutions is 3.16 x 10(-3) S/cm at 300A degrees C and similar to 2 x 10(-2) S/cm at 700A degrees C. The high rubidium ion conductivity of the synthesized solid electrolytes is mainly due to the formation of rubidium vacancies when Nb5+ or Ta5+ substitutes for Al3+ and to the specific features of the crystal structure of RbAlO2.