Rietveld Study of the Changes of Phase Composition, Crystal Structure, and Morphology of BiFeO3 by Partial Substitution of Bismuth with Rare-Earth Ions

Abstract

BiFeO3 is an interesting material due to its multiferroic properties. It attracts attention due to its potential applications in spintronics and in microelectronics for data storage, among others. Single-phase bulk material from BiFeO3 is difficult to synthesize. The kinetics of perovskite phase formation most often leads to the presence of impurity phases. It has been shown that low levels of replacement of Bi with rare earth ions lead to stabilization of the perovskite phase. In the present work, Rietveld refinement of the crystal structure based on powder X-ray diffraction patterns was applied to study the influence of partial substitution of Bi by rare-earth (RE) elements with different ionic radii on structural and morphological properties of the ferrite phase. Substitution by large RE ions was found to preserve the rhombohedral symmetry of BiFeO3, whereas substitution by smaller RE ions led to the coexistence of two polymorphic perovskite phases with rhombohedral R3c and orthorhombic Pnma symmetries. The unit cell parameters as well as the interatomic distances and angles, not only around the A cation but also around the iron ions, were influenced by the substitution. The mean crystallite and particle size decreased with the decrease of ionic radius of substituting RE ion.

Effect of heavy rare‐earth substitution on physical properties of BiFeO3 thin films and their photocatalytic application

“…Our structural analysis indicated a complete structural phase transition from a rhombohedral to a lower‐symmetry orthorhombic structure for x = 0.1 and r RE3+ ≤ 1.25. The XRD peaks of Bi 0.9 RE 0.1 FeO 3 ( r RE3+ ≤ 1.25) can be completely indexed to orthorhombic structure with space group Pnma 31,32 . Moreover, the shift of all the peaks toward higher 2 θ angles at the lower level of the RE substitution indicates a decrease in the unit cell volume (see Figure 1e).…”

“…As seen in Figure 1b–d, after RE 3+ substitution for Bi 3+ into BFO, the structural phase transition from rhombohedral to orthorhombic structure has only appeared for Bi 1− x RE x FeO 3 ( x = 0.00, 0.05) thin films. It is due to the disappearance of (0 0 6) R and (2 0 2) R reflections, and the appearance of (2 2 0) O and (0 2 2) O lines, (0 2 4) R reflection to double (2 0 2) O , (0 4 0) O lines, as well as (0 1 8) R and (2 1 4) R reflections to a triplet (3 2 1) O , (2 4 0) O , (0 4 2) O lines 31,32 . The coexistence of rhombohedral and orthorhombic phases for sample Bi 0.1 Gd 0.9 FeO 3 can induce microstrains that affect the physical properties of the RE‐substituted BFO structure.…”

“…No secondary and impurity phases are observed, and all XRD patterns confirm the formation of single-phase samples. As seen in Figure 1b-d, after RE 3+ substitution for Bi 3+ into BFO, the structural phase transition from rhombohedral to orthorhombic structure has only 31,32 The coexistence of rhombohedral and orthorhombic phases for sample Bi 0.1 Gd 0.9 FeO 3 can induce microstrains that affect the physical properties of the RE-substituted BFO structure. Our structural analysis indicated a complete structural phase transition from a rhombohedral to a lower-symmetry orthorhombic structure for x = 0.1 and r RE3+ ≤ 1.25.…”

Crystal structure and magnetocaloric effect of non-rare-earth KBa8Fe12(Bi6−xFex)O38

“…These show the reliability of the Rietveld refinement results. 18,19 As shown in the unit cell structure diagram (Fig. 2b), the crystal structure of KBa 8 -Fe 12 (Bi 6−x Fe x )O 38 (x = 0.2, 1.1, 2.0, 2.9, and 3.8) is body-centered cubic with the space group Pm3 ¯m.…”

Editorial for the Special Issue “The Rietveld Method in Geomaterials Characterisation”

“…In a similar study of a synthetic perovskite type compound BiFeO 3 [3], the Rietveld refinement of the crystal structure, based on powder X-ray diffraction patterns, was applied to study the influence of the partial substitution of Bi by rare-earth (RE) elements with different ionic radii on the structural and morphological properties of the ferrite phase. Substitution by large RE ions was found to preserve the rhombohedral symmetry of BiFeO 3 , whereas substitution by smaller RE ions led to the coexistence of two polymorphic perovskite phases with rhombohedral R3c and orthorhombic Pnma symmetries.…”