Structure, dielectric and magnetodielectric properties of Bi_1-xGd_xFeO₃ Ceramics

Different magnetodielectric effects were observed in Bi_1-xGd_xFeO₃ ceramics depending on gadolinium content. A positive one was observed in the samples with x ≤ 0.10 at 295 K and 16 K, and a negative one in the sample with x = 0.4 at 16 K. Structure analysis by x-ray diffraction (XRD) reveals that the samples crystallize in the R3c structure (ferroelectrics) for x < 0.08 and in the Pbnm structure (paraelectrics) for x ≥ 0.3 at room temperature. Temperature-dependent dielectric response and x-ray diffraction confirm the occurrence of a structural transition in the Pbnm phase at low temperature for the samples with x ≤ 0.4. While the positive magnetodielectric effects can be attributed to a coupling of magnetic and crystallographic structures of the R3c phase, the observed negative magnetodielectric effect in the Pbnm phase can be associated with a low-temperature modification of the Pbnm structure. The observed dual-signed magnetodielectric effects suggest that the Bi_1-xGd_xFeO₃ oxides are a good prototype for understanding the magnetodielectric coupling mechanism in this kind of materials.