Composition-property correlation in Eu-substituted BiFeO3 Spark Plasma Sintered ceramics

Bi1-xEuxFeO3 (x = 0 – 0.20) powders were obtained by a sol-precipitation method, using bismuth and iron nitrates as starting materials. After thermal treatment at 600 °C/1 h, well-crystallized particles with sizes ranged... [ view full abstract ]

Bi_1-xEu_xFeO₃ (x = 0 – 0.20) powders were obtained by a sol-precipitation method, using bismuth and iron nitrates as starting materials. After thermal treatment at 600 °C/1 h, well-crystallized particles with sizes ranged between 40 and 155 nm, where obtained when the Eu³⁺ content decreases from x = 0.20 to x = 0.

For a substitution degree x ≤ 0.10 only the rhombohedral form of BiFeO₃ was identified by XRD. The increase of europium addition above this value induces the partial conversion of the rhombohedral (R3c) modification into the orthorhombic (Pnma) polymorph. From these powders, fine-grained ceramics were prepared by spark plasma sintering (SPS).

FE-SEM investigations indicated that the presence of Eu³⁺ as solute on Bi sites determines a strong decrease of the grain size from 925 nm for x = 0 to 173-217 nm for x ≥ 0.05.

The ceramics exhibit decreased values of permittivity when increasing the Eu³⁺ content. The structural transition has a beneficial effect on the dielectric losses which decrease with about one order of magnitude from tanδ ~ 0.07 (x = 0) to ~ 0.005 (x = 0.20) at fixed frequency f = 100 kHz. In the temperature range of 400 – 500 K, relaxation phenomena occur for x ≤ 0.15.

Magnetic hysteresis loops collected on the ceramics showed an antiferromagnetic behaviour for x = 0 and x = 0.20 and a weak ferromagnetic behaviour for 0.05 ≤ x ≤ 0.15.