although the degree of ion conductivity was slightly reduced when even a small amount of sio 2 was added to the aformentioned material as a sintering additive there was no change in relative effects observing the composition limits of 1 x y zro 2 xsc 2 o 3 yal 2 o 3 where 0 07 lt x y lt 0 13 and 0 005 u2266 y u2266 0 02 the powdered materials were combined so as to attain the composition limits shown in table 4 and then were well mixed to form pellets of a diameter of 20 mm and a thickness of 2 mm these pellets were sintered for 60 hours at 1620 u00b0 c in air and in this manner a plurality of test ion conductors were produced after characterizing the crystal structure of the test materials using powder x ray diffraction the ion conductivity was determined from measurements of their complex impedance in the frequency range 10 hz u02dc 1 mhz with an impedance analyzer table 4 shows the results for the degree of ion conductivity of each test material at 800 u00b0 c when measured by the same method as used in example 1 table 4______________________________________test conductivitymater composition of ohm sup 1ial test material cm sup 1 ______________________________________20 0 93 zro sub 2 0 065 sc sub 2 o sub 3 0 005 al sub 2 o sub 3 6 8 u00d7 10 sup 221 0 92 zro sub 2 0 075 sc sub 2 o sub 3 0 005 al sub 2 7 5 u00d7 10 sup 222 0 91 zro sub 2 0 085 sc sub 2 o sub 3 0 005 al sub 2 8 8 u00d7.