By intentionally varying the mixing ratio to nonstoichiometric region, spon
taneous dispersion of the Zr2O(PO4)(2) secondary phase was successfully ach
ieved and the Mg2+ ion conductivity was greatly improved by considerably in
creasing the relative density of the composite and the Mg2+ ion conducting
composite showing the highest ion conductivity among the Mg2+ ionic conduct
ors reported was developed.