IONIC-CONDUCTION BEHAVIOR IN ZIRCONIUM-PHOSPHATE FRAMEWORK

A series of M(I)Zr2(PO4)3 (M(I)ZP; M=Li, Na, K, Rb, Cs and Ag) solid electrolytes have been investigated. The crystallographic and electrochemical properties of M(I)ZP are compared with those of M(II)Zr4(PO4)6 (M(II)ZP).M(I)ZP and M(II)ZP crystallized in the NASICON- and beta-Fe2(SO4)3-structures: The crystal structure was determined by the size of the guest cation. The ionic conductivity of the NASICON-type compound was highly sensitive to the size of the guest (i.e., mobile) cation, whereas that of the beta-Fe2(SO4)3-type one was slightly size-dependent. This difference is expected to arise from the difference in the nature of site in which mobile cation is accommodated; a six coordination site of the NASICON-type structure and a four coordination one of the beta-Fe2(SO4)3-type StruCtUre. M(I)ZP showed ca. two or three orders higher conductivity than M(II)ZP, when they have almost the same ionic radius of mobile cation. AgZP, CdZP, and BaZP, in which mobile cations have high polarizability, showed high conductivities for the size of the mobile cations.