Ultrasonic investigation of Y ³⁺ -induced modifications in the elastic properties of yttrium iron garnet

An investigation was carried out to examine how varying levels of Y3+ substitution (0.0 ≤ x ≤ 0.6) influence the structure, morphology and elastic behaviour of polycrystalline Y3+xFe5-xO12 garnets at 300 K. X-ray diffraction revealed a structural transformation from uniphasic (x = 0.0, 0.2) to dual phasic (x = 0.4, 0.6) as Y3+ replaced Fe3+. This substitution significantly influenced the microstructure. Elastic properties, comprising bulk (B), shear (G), Young’s (E) moduli, Debye temperature (θ), Poisson’s ratio (σ) and microhardness (Hv), were determined using an unrivalled precise ultrasonic pulse transmission technique. The results showed a systematic variation in elastic parameters with composition, indicating that Y3+ -substitution alters the garnet’s mechanical stiffness and bonding properties. A reduction up to 56 ± 6% in zero-porosity-corrected values of B0, G0 and E0 was observed. These changes were attributed to atomic packing, bond strength, secondary phase formation and microstructural changes. The material exhibited brittle characteristics, confirmed by the B0/G0, G0/B0 and σ0 ratios. Elastic stiffness (Cij), compliance (Sij) and magnetostriction (λ) constants were approximated for single-crystalline counterparts. The difference in lattice potential energies between polycrystalline and single-crystal garnets (ULS > ULP) was discussed, emphasising the role of grain boundaries, pores and microcracks.