Stiffening of phonons with enhanced hybridization and structural phase transformation upon Pr-doping in BiFeO3

Highlights: • Structural transition in Bi1.1-xPrxFeO3 from rhombohedral (R3c) to orthorhombic (Pnma). • Contraction of octahedral bond and induce strain in the lattice gives strength in Bi–O bond. • Stiffening of low frequency Raman modes is understood by the BOLS correlation mechanism. • The effect of hybridization strength of O 2p orbitalswith neighboring atoms in structural phase transition. -- Abstract: Bi_1.1-xPr_xFeO₃ (x = 0.00, 0.10, 0.15 and 0.20) samples were synthesized and their structural study was carried out using X-ray diffraction which manifests structural phase transformation for x > 0.15 from rhombohedral (R3c) to orthorhombic (Pnma) crystal symmetry, which is further confirmed by micro-Raman spectroscopy. The stiffening of phonon modes with increasing Pr-doping fraction has been attributed to the development of local stress in the lattice, reduction in bond length in the framework of the bond-order-length-strength correlation mechanism. Electronic structure studies carried out using soft x-ray absorption spectroscopy shows that O 2p orbitals exhibit enhanced hybridization with neighboring atoms. Moreover, the +3 valence states of Fe and Pr are also confirmed using Fe L-edge and Pr M-edge spectra and found to agree with Raman studies. These investigations provide evidence of the correlation between the bond--length and hybridization on such structural phase transformation in multiferroic materials.