ymgo zmno tre sub 2 o sub 3 where x u2266 0 06 0 005 u2266 y u2266 0 08 0 005 u2266 z u2266 0 02 0 005 u2266 t u2266 0 02 in the composition formula re indicates at least one of y gd dy ho er and yb application_number US 83810792 A description description is now made of a non restrictive embodiment of the present invention first batio 3 cazro 3 mgco 3 and mnco 3 and a rare earth oxide are weighed on the basis of respective compositions shown in table 1 and table 2 and an additive shown in table 3 and table 4 is weighed at ratios shown in the tables 3 and 4 to obtain starting materials for samples nos 1 to 39 5 by weight of a water soluble vinyl acetate binder is added to each of the starting materials for the samples nos 1 to 38 prepared in the above described manner followed by wet blending for 16 hours a ceramic slurry obtained by the above described blending is dried at a temperature of 150 u00b0 c and then is classified using a 60 mesh screen ceramic particles obtained by the classification are formed by applying a pressure of 2 t cm 2 to fabricate a disk shaped disk having a diameter of 10 mm the disk shaped disc obtained is calcined at a temperature of 300 u00b0 c and in an atmosphere.