Structural, vibrational, and enhanced magneto-electric coupling in Ho-substituted BiFeO₃

The effect of Holmium (Ho) substitution in BiFeO₃ [Bi_1-xHo_xFeO₃ (x = 0.00, 0.05, 0.10, 0.15, 0.18, and 0.20)] ceramics is reported. The X-ray diffraction study shows composition-driven rhombohedral-to-orthorhombic (R3c to Pnma) phase transition for Bi_1-xHo_xFeO₃ (x = 0.15, 0.18, and 0.20) which is confirmed by Reitveld refinement. Raman spectra of Bi_1-xHo_xFeO₃ (x = 0.00, 0.05, and 0.10) belong to the rhombohedral (R3c) structure. Further increasing the Ho³⁺ concentration in a BiFeO₃ (BFO) system revealed that Raman modes of Bi_1-xHo_xFeO₃ (x = 0.15, 0.18 and 0.20) were assigned to an orthorhombic (pnma) structure, which is confirmed by the Rietveld analysis of X-ray diffraction data and TEM analysis. Ferroelectric studies show that the remnant polarization (P_r) gradually decreases for Bi_1-xHo_xFeO₃ (x = 0.15, 0.18, and 0.20), confirming the transformation from polar to non-polar systems. Magnetic measurement shows ferromagnetic behavior observed for Bi_1-xHo_xFeO₃ (x = 0.10 and 0.20) samples. Further, the magneto-electric coupling is measured in terms of magneto-capacitance of Ho³⁺-substituted BiFeO₃ samples.