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

The effect of Holmium (Ho) substitution in BiFeO3 [Bi1-xHoxFeO3 (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 Bi1-xHoxFeO3 (x = 0.15, 0.18, and 0.20) which is confirmed by Reitveld refinement. Raman spectra of Bi1-xHoxFeO3 (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 Bi1-xHoxFeO3 (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 (Pr) gradually decreases for Bi1-xHoxFeO3 (x = 0.15, 0.18, and 0.20), confirming the transformation from polar to non-polar systems. Magnetic measurement shows ferromagnetic behavior observed for Bi1-xHoxFeO3 (x = 0.10 and 0.20) samples. Further, the magneto-electric coupling is measured in terms of magneto-capacitance of Ho3+-substituted BiFeO3 samples.