PURPOSE: To obtain a conductive material for oxygen ion having a small activation energy and high oxygen ion conductivity at low temp. by using specified compd. as the main component and forming a hexagonal crystal structure as the main structural phase of a sintered compact.

CONSTITUTION: This conductive material for oxygen ion is obtd. by mixing La2O3, Ce2O3, Pr2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3 as the source material of rare earth elements and precipitated silica, silica gel, crystalline silica, or the like as the source material of SiO2 in a specified proportion, kneading the mixture in an alcohol by using a ball mill, drying, calcining at 1000°C, pulverizing the calcined material, and then sintering at 1300-1700°C. The conductive material for oxygen ion consists essentially of LnxSi6O(3x/2)+12, wherein Ln is tervalent rare earth element such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy and x ranges 6<x<12. By the X-ray diffraction analysis of one example of this conductive material for oxygen ion, the crystal system of the main structural phase is hexagonal. Fig.(A) shows the view along the c-axis and Fig.(B) shows the view along the a-axis.