Ho and Ti Co-Substitution Tailored Structural Phase Transition and Enhanced Magnetic Properties of BiFeO₃ Thin Films

Abstract

The polycrystalline thin films of BiFeO3 (BFO) and Bi0.90Ho0.10Fe1–xTixO (x = 0, 0.025, 0.05, 0.10, 0.15, and 0.20) were successfully synthesized by the simple sol–gel method. X-ray diffraction and Raman spectra revealed the substitution of Bi and Fe by Ho and Ti, respectively, and correspondingly a structural phase transition from the rhombohedral phase to orthorhombic phase. The field-emission scanning electron microscopy and transmission electron microscopy images indicated that the average size of the particles was decreased and the surface homogeneous agglomeration was enhanced with the increased concentration of Ti to x = 0.05. The X-ray photoelectron spectroscopy measurements illustrated that Fe3+ and O2– ions tended to increase with the Ti concentration increase, which accounted for the enhanced super-exchange interaction between Fe3+ and O2–. Because of the reduced concentration of oxygen vacancies, Ho and Ti ions with a smaller ionic radius and denser surface structure, the Ho and Ti co-substituted films with an appropriate concentration of Ti (x = 0.05) showed an optimal saturation magnetization (M s) of 44.23 emu/cm3 and remanent magnetization (M r) of 4.62 emu/cm3, which were approximately 1.8 times and 1.9 times than that of the pure BFO, respectively. This work opened up an effective way to modulate the structure and properties of BFO-based materials.

Augmentation of optical and magnetic characteristics at ambient temperature in bismuth ferrite-titanium (BiFe1–xTixO3) multiferroic compounds

“…Prevailing literature indicates that both Fe 3+ and Fe 2+ ions coexist within BFO matrices [19,29]. The Fe 2+ ion is known to contribute to magnetic anisotropy, whilst the Fe 3+ ion is anticipated to exhibit isotropic behavior due to its electronic configuration.…”

“…This particular substitution was chosen because the ionic radius of Ti 4+ (0.645 Å) closely approximates that of Fe 3+ (0.645 Å), which favors a distorted rhombohedral symetry with an R3c space group and facilitates significant polarization along the [001] hexagonal or [111] pseudocubic direction [17]. Furthermore, it is anticipated that substituting Fe 3+ with Ti 4+ would decrease the leakage current density and enhance the ferroelectric properties of BFO [18] Ti 4+ acts as a donor within the oxygen octahedra framework, mitigating oxygen vacancy formation, and preventing the valence fluctuation from Fe 3+ to Fe 2+ [19]. Prior investigations into Ti 4+ substitution for Fe 3+ have demonstrated that lattice strains and defects, resultant from the disparity in ionic radii, inhibit grain growth as the level of substitution increases.…”

Improved Optical, Multiferroics, and Photocatalytic Properties of Bi1−xSmxFe1−ySnyO3 Nanoparticles Synthesized by Sol–Gel Method

“…These saturation magnetization values are consistent with earlier reported studies. [19,20] In bulk BFO, the spiral arrangements of magnetic spins with a wavelength of 62 nm tend to suppress magnetization. [1][2][3] However, in small particles, this periodicity of spin cycloid can be disrupted as their size decreases to 62 nm.…”

Simple Low Temperature Technique to Synthesize Sillenite Bismuth Ferrite with Promising Photocatalytic Performance

“…Bismuth ferrites, a large group of transition-metal oxides, including perovskite, mullite, and sillenite-type structural compounds have lately sparked the interest of researchers due to their superior fundamental physics and wide-ranging technological applications. , Among them, perovskite-type BiFeO 3 (BFO) with a suitable band gap of ∼2.2 eV and the existence of simultaneous ferroelectric and ferromagnetic ordering at room temperature is mostly studied in the field of visible-light responsive photocatalysis . Compared to perovskite BFO, the synthesis and analysis of other phases such as sillenite-type Bi 25 FeO 40 with the I 23 cubic crystal structure are yet less explored. , The sillenite compounds, bearing the general formula of Bi 12 MO 20 (M = Ge, Ti, Ga, Fe, Bi, V, etc), exhibit unique properties such as photo-refractivity, optical activity, and photo-conductivity .…”