Structure-Substitution Limit Correlation Study on Cr3+ Substituted Polycrystalline Yttrium Iron Garnet

Polycrystalline samples of Cr3+ - substituted yttrium iron garnet (Y3Fe5O12) system with general chemical formula, Y3Fe5-xCrxO12, x = 0.0, 0.2, 0.4 and 0.6 were synthesized by double sintering ceramic technique and characterized by X-ray powder diffractometry. The Rietveld fitted X-ray diffraction patterns analysis revealed mono phase formation for x = 0.0 - 0.4 compositions while x = 0.6 composition possesses mixed phase character. The observed substitution limit has been discussed in the light of ionic size of substituent, electrostatic energy, electronic configuration and synthesis parameters. These observations strongly suggest that the electronic configuration of Cr3+, which is favorable to the formation of d2sp3 (octahedral) type bonds, must be important. In the case of Cr3+, the substitution does not appear to proceed well for x much greater than 0.5, this limitation probably is a consequence of the strong preference of a smaller ion Cr3+, for a larger octahedral site which quickly leads to a condition not comparable with the requirement of the structure. The distribution of cations, mean ionic radii and theoretical lattice constant values have been determined.