Jieyu Chen

Improved ferroelectric and leakage current properties of Er-doped BiFeO3 thin films derived from structural transformation

Multiferroic pure and Er-doped BiFeO3 thin films were prepared using a sol–gel technique. The effect of Er-doped concentration on the crystal structure and on the ferroelectric and leakage current properties of BiFeO3 films were studied in detail. The study showed the enhanced ferroelectric polarization and reduced leakage current density that occurred after doping Er. Such improved ferroelectric and leakage properties are attributed to ferroelectric distortion and to the change of leakage current conduction mechanisms derived from the structural transformation that occurred after doping Er. The rhombohedral structure of pure BiFeO3 transforms to the coexistence of tetragonal and orthorhombic symmetry structure as Er-doped concentration x increased gradually to 0.15, then to the orthorhombic structure when x = 0.20. The present work provides an easy method to decrease the leakage current and improve the ferroelectric properties of BiFeO3 films.

Domain switching contribution to the ferroelectric, fatigue and piezoelectric properties of lead-free Bi0.5(Na0.85K0.15)0.5TiO3 films

Lead-free Bi0.5(Na0.85K0.15)0.5TiO3 films have been prepared via a solution-gelation technique. The microstructure, domain structure, ferroelectric, fatigue and piezoelectric properties were investigated systematically. This shows that the films have a single-phase perovskite structure and show outstanding ferroelectric, fatigue and piezoelectric properties at room temperature. The maximum piezoelectric coefficient value of the films reaches approximately 158.94 pm V−1, which is comparable to that of polycrystalline lead-based films. Thus good ferroelectric, fatigue and piezoelectric properties are attributed to the well-defined electrical domain structure and its switching for Bi0.5(Na0.85K0.15)0.5TiO3 films. The present results suggest that Bi0.5(Na0.85K0.15)0.5TiO3 films can be used as a candidate for lead-free films in piezoelectric micro-electro-mechanical systems.

Effects of Ho, Mn co-doping on ferroelectric fatigue of BiFeO3 thin films

AbstractHo, Mn, and Ho, Mn co-doped BiFeO3 thin films were deposited on Pt (100)/Ti/SiO2/Si substrates using solution gelation. The ferroelectric fatigue properties were clearly improved after doping with Ho and Mn. The doped BiFeO3 thin film displayed more strongly increased ferroelectric, leakage current, and fatigue properties compared with the pure BiFeO3 thin film. Thus, the improved performance of the BiFeO3 thin films depends on the structural transformation and reduced oxygen vacancy concentration. The present work provides a feasible approach to enhance the ferroelectric and fatigue properties of BiFeO3-based thin films.

Magnetoelectric coupling effect in lead-free Bi4Ti3O12/CoFe2O4 composite films derived from chemistry solution deposition

Lead-free magnetoelectric composite films combining Bi4Ti3O12 and CoFe2O4 were synthesized by chemical solution deposition on Pt (100)/Ti/SiO2/Si substrate. Morphological and electrical domain structure, ferroelectric, leakage, dielectric, piezoelectric, magnetic and magnetoelectric properties were investigated for Bi4Ti3O12/CoFe2O4 composite films. Well-defined interfaces between Bi4Ti3O12 and CoFe2O4 film layers and electrical domain structure were observed. The composite films show the coexistence of ferroelectric and ferromagnetic orders at room temperature. Larger piezoelectric coefficient and magnetization are obtained for the composite films, which is contributed to the magnetoelectric effect since it originates from the interface coupling through mechanical strain transfer. This work presents a feasible way to modulate the magnetoelectric coupling in ferromagnetic/ferroelectric composite films for developing lead-free micro-electro-mechanical system and information storage devices.

Improved ferroelectric and leakage properties of Ce doped in BiFeO 3 thin films

Ce doped BiFeO3 thin films with a perovskite structure were prepared using solution-gelation method. It shows that the ferroelectric properties have been enhanced after doping Ce. The enhanced ferroelectric properties are attributed to the structural transformation and the reduced leakage current after doping raremetal of Ce. It has been found that the phase structures of the films transfer from rhombohedral symmetry structure to the coexistence of the tetragonal and orthorhombic symmetry structure. And Fe2+ ions have been reduced, which leads to the decreased leakage for Ce doped BiFeO3 thin films. The present work can provide an available way to improve the ferroelectric and leakage properties for multiferroic BiFeO3 based thin films.

Magnetoelectric fatigue of Ho-doped Bi5Ti3FeO15 films under the action of bipolar electrical cycling

Pure and Ho-doped Bi5Ti3FeO15 magnetoelectric films were prepared by a sol–gel method, and the influence of bipolar electrical cycling on the ferroelectric, leakage and magnetoelectric properties of the films were studied in detail. It was demonstrated that the ferroelectric, leakage, and especially the magnetoelectric performance are depressed significantly after 109 bipolar electric cycles for the pure Bi5Ti3FeO15 films. The ferroelectric and leakage fatigue behaviors are attributed to the defect dipoles and other agglomerated space charges on the surface after bipolar electrical cycling, which further results in magnetoelectric fatigue. In comparison, Ho-doped Bi5Ti3FeO15 films show much stronger fatigue resistance than Bi5Ti3FeO15 films. The ferroelectric polarization and magnetoelectric coefficient only slightly decreased after doping with Ho. The good magnetoelectric fatigue resistance mainly derives from the depression of ferroelectric and leakage fatigue. The present work provides a possible way to improve the anti-fatigue behaviors of magnetoelectric films for application in functional devices.

Optical and Magnetic Properties of Copper Doped Zinc Oxide Nanofilms

Copper doped Zinc Oxide nanofilms were prepared using a simple and low cost wet chemical method. The microstructures, phase structure, Raman shift and optical absorption spectrum as well as magnetization were investigated for the nanofilms. Room temperature ferromagnetism has been observed for the nanofilms. Structural analyses indicated that the films possess wurtzite structure and there are no segregated clusters of impurity phase appreciating. The results show that the ferromagnetism in Copper doped Zinc Oxide nanofilms is driven either by a carrier or defect-mediated mechanism. The present work provides an evidence for the origin of ferromagnetism on Copper doped Zinc Oxide nanofilms.

Magneto-dielectric and magnetoelectric anisotropies of CoFe2O4/Bi5Ti3FeO15 bilayer composite heterostructural films

Bilayer composite heterostructural films consisting of magnetic CoFe2O4 and multiferroic Bi5Ti3FeO15 films were prepared by the chemical solution deposition method. Morphological, ferroelectric, piezoelectric, magnetic, magneto-dielectric and magnetoelectric properties were investigated for CoFe2O4/Bi5Ti3FeO15 composite films. The magneto-dielectric and magnetoelectric effects are observed for the composite films, which is attributed to the enhanced interface coupling and mechanical strain transfer due to the small lattice mismatch between CoFe2O4 and Bi5Ti3FeO15 film layers. Magneto-dielectric and magnetoelectric anisotropies were also observed for the composite films. Correspondingly, the in-plane and out-of-plane magnetoelectric voltage coefficients reach 57 mV cm−1 Oe−1 and 78.9 mV cm−1 Oe−1, respectively. Thus magneto-dielectric and magnetoelectric anisotropies originate from the magnetic anisotropy of CoFe2O4/Bi5Ti3FeO15 composite films. The present work provides promising candidates for applications in magnetoelectric devices.

The ferroelectric and fatigue behaviors of Dy doped BiFeO3 thin films prepared by chemistry solution deposition

Single-phase multiferroic BiFeO3 and rare-earth metal of dysprosium (Dy) doped BiFeO3 thin films were prepared by chemistry solution deposition. The structure and electrical properties of the BiFeO3 thin films were characterized and investigated. It shows that improved ferroelectric polarization, fatigue endurance and leakage current were obtained. Thus enhanced performance are attributed to the lattice distortion happened along with the structure transformation from the rhombohedral structures toward the coexistence of tetragonal and orthorhombic symmetry structures and the decreased oxygen vacancies after doping Dy. The present work provided an available way on enhancing ferroelectric polarization and fatigue endurance of BiFeO3 based thin films.

Enhanced Multiferroic Properties of Eu-Doped BiFeO3 Thin Films Derived from Rhombohedral–Tetragonal Phase Boundary

Eu-doped BiFeO3 multiferroic thin films were prepared using a sol–gel technique. The effect of Eu3+ ion substitutional doping on the multiferroic properties of BiFeO3 thin films was investigated in detail, revealing obvious enhancement of ferroelectricity and ferromagnetism. The enhanced multiferroic properties are attributed to phase boundary, where two phases with rhombohedral and tetragonal structure coexist. Both x-ray diffraction analysis and Raman spectroscopy confirmed that BiFeO3 thin films with 5% Eu doping (Bi0.95Eu0.05FeO3) undergo a phase transformation from a rhombohedral to tetragonal structure. Thus, it is suggested that there is rhombohedral– tetragonal phase boundary in Bi0.95Eu0.05FeO3 thin films. Additionally, the leakage current density of the thin films decreased under high electric field after Eu doping, which is attributed to a change of the leakage current conduction mechanism related to the formation of rhombohedral–tetragonal phase boundary. The present work provides an easy method to enhance the multiferroic properties of BiFeO3-based thin films.