Abstract: Complex ceramic oxides of the general formula Mg2MM?O6+x where M=Rare metal ion or Yttrium or Lanthanum and M?=Sn, Sb, Zr, Hf, Ta, and Nb; and where ?0.5<x<0.5; having a defective pyrochlore structure are useful for active and passive electronic applications, as dielectrics, catalyst sensors, hosts for radioactive waste, etc. This process for the preparation of this class of compounds comprises: (i) mixing the compounds of magnesium, M and M? to get the molar ratio as 2:1:1 (ii) the mixture obtained in step (i) along with a wetting medium may be ball milled or mixed; (iii) the resultant slurry may be dried to obtain dry powder, (iv) the resultant mixture may be heated to a temperature in the range of 1000-1600° C. for the duration ranging from 3 hours to 50 hours, either in a single step or by taking out the reactant after heating, checking for the structure formation and heating again after grinding, if necessary.

Abstract: This invention relates to a new group of complex ceramic oxides and a process for their production. This group of novel complex ceramic oxides are of the general formula Mg2MM?O6+x, where M=Rare Earth metal ion or Yttrium or Lanthanum and M?=Sn, Sb, Zr, Hf, Ta, and Nb; and where ?0.5<x<+0.5; and have a defective pyrochlore structure. Minor variations in the compositions up to 8% in any of the metal ions may be tolerated for the formation of the required phase. The process for the preparation of the novel class of compounds comprises: (a) Mixing the compounds of magnesium, M and M? (where M may be Yttrium, Lanthanum or any of the Rare Earth metals; and M?=Antimony, Tin, Zirconium or tantalum) in such a way as to get the molar ratio of Mg:M:M? as 2:1:1 required for the formation of the compounds of the general formula Mg2MM?O6+x. Minor variations in the compositions up to 8% in one metal ions may be tolerated for the formation of the required phase.