New bismuth ion conducting solid electrolyte

A new trivalent bismuth ion conducting solid electrolyte, (Bi_xGe_1 − x)_{4/(4 − x)}Ta(PO₄)₃, was successfully developed by selecting the NASICON-type GeTa(PO₄)₃ as the mother solid. Although bismuth has two kinds of valence states of + 3 and + 5, it was clear that pure trivalent Bi³⁺ ion conduction, without any electronic conduction by a valence change of bismuth in the oxygen pressure range over 10^− 3 Pa, was realized by selecting the crystal structure and constituents of the solid.