Effect of Fe3+ substitution on elastic properties of yttrium iron garnet

The effect of Fe3+ substitution on the elastic properties of yttrium iron garnet (Y3-xFe5+xO12, x=0.0, 0.1, 0.3 and 0.5) was studied by means of x-ray diffraction, scanning electron microscopy and ultrasonic pulse transmission technique at 300 K. Elastic moduli of the specimens were computed and these are corrected to the void-free state by employing different models. Contrary to expectation, the magnitude of elastic constants is found to decrease with increasing Fe3+ substitution. The lowering of elastic stiffness is mainly due to residual stress-induced spontaneous cracking in the material and its development on increasing grain size with Fe3+ substitution in the system. The variation of elastic moduli and the lower value of lattice energy for polycrystalline specimens as compared to its single crystalline counterpart were explained in the light of various structural and microstructural parameters and the grain boundary misorientation effect.