Defect structure and electrical and magnetic properties of calcium manganese vanadium garnets

Calcium manganese vanadium garnets were characterized by x-ray diffraction, electron spin resonance, and conductivity measurements. The stability rang e of Ca-2.25 Mn-+ x(2.25) - xV3O12 Was shown to be 0.25 I x less than or eq ual to 0.75. The ionic transport in the garnets studied is due to both vaca ncies and interstices in the composition range x < 0.25 and only interstice s for x greater than or equal to 0.25. The manganese ions are coupled by an tiferromagnetic exchange. It is suggested that the stability limits of M-2. 25 M+ x'(2.25) (-) xV3O12 vanadium garnets depend on the ratio of ionic rad ii k = R-M/R-M'. For k greater than or equal to 1.25, the stoichiometry ran ge of M-2.25 (+) M-x'2.25 - xV3O12 is 0.25 less than or equal to x less tha n or equal to 0.50; at k = 1.14, the stability limits are at x = 0.25 and 0 .75.