Rongli Gao

Electric Control of the Hall effect in Pt/Bi0.9La0.1FeO3 bilayers

Platinum metal, being nonmagnetic and with a strong spin-orbit coupling interaction, has been deposited on weak ferromagnetic Bi0.9La0.1FeO3 thin films. The Hall effect is studied as a function of the polarization direction of multiferroic Bi0.9La0.1FeO3 thin films, as well as magnetic field (H) and temperature (T). For the two polarization directions, besides the obvious difference of the anomalous Hall resistance RAH, it increases sharply with decreasing temperature, and even changes sign, thus violating the conventional expression. This observations indicate local magnetic moments in Pt caused by the local electric fields at the interface of Bi0.9La0.1FeO3 films. Also, possible proximity effects and induced magnetic ordering in Pt on weak ferromagnetic Bi0.9La0.1FeO3 thin films of both upward and downward polarization states may exist and their contribution to the spin-related measurements should not be neglected.

Effects of Sn doping on the microstructure and dielectric and ferroelectric properties of Ba(Zr0.2Ti0.8)O3 ceramics

Ba(Zr0.2Ti0.8)1−xSnxO3 ceramics are prepared via the conventional solid state reaction method. The effects of Sn doping on microstructure, dielectric and ferroelectric properties of Ba(Zr0.2Ti0.8)1−xSnxO3 ceramics were investigated. These results indicate that Sn4+ ions enter the unit cell maintaining the perovskite structure of solid solution and substitute preferentially for Zr4+ and then Ti4+ when Sn content (x) gradually increases from 0 to 0.2. Introduction of Sn4+ on B sites makes grain more uniform and regular. The addition of Sn4+ results in the fall of the Curie temperature. The temperature dependences of dielectric properties of Ba(Zr0.2Ti0.8)1−xSnxO3 ceramics indicate that the addition of stannum leads to the enhancement of the diffuseness of ferroelectric–paraelectric phase transition. Moreover, it can be found that the ferroelectric properties deteriorate as Sn content increases.

Microstructure, dielectric and ferroelectric properties of (1− x ) BaTiO 3 – x BiYbO 3 ceramics fabricated by conventional and microwave sintering methods

Abstract(1−x) BaTiO3–xBiYbO3 (abbreviated as (1−x) BT−xBY, x = 0, 0.03, 0.06 and 0.09) ferroelectric ceramics have been fabricated by conventional sintering (CS) and microwave sintering (MWS) methods. The microstructure, dielectric and ferroelectric properties of (1−x) BT–xBY ceramics have been investigated systematically. X-ray diffraction patterns indicate all samples possess single perovskite phase and the crystal structure transforms from tetragonal to pseudo-cubic phase with increasing x. It can be also found that denser microstructure and finer grains can be obtained by MWS compared to CS as indicated by scanning electron microscopy. Dielectric measurements reveal that the addition of BY can lead to an obvious relaxation behavior in all samples, and the relaxation characteristics of MWS samples are stronger than those of CS samples. Moreover, the dielectric constant decreases with increasing BY content and the temperature stability and frequency stability of dielectric properties can be enhanced by using MWS method and addition of BY. P–E hysteresis loops become slimmer with the increase of BY content, and the ferroelectric properties of MWS samples are similar to those of CS samples. The leakage current of MWS sample is smaller than that of CS sample from J–E curve. The energy storage efficiency (η) increases with increasing BY content, while the energy storage density (U) increases and then decreases, Umax is obtained at x = 0.06. These results demonstrate that MWS technique and moderate BY content are effective methods to prepare materials for energy storage application.

Study on the structure and properties of (1-x) BiYbO3-xBaTiO3 ceramics synthesized by sol–gel method

ABSTRACT (1-x) BiYbO3-xBaTiO3 (short for BY-BT) lead-free ferroelectric ceramics were synthesized by solid state reaction method. The microstructure, dielectric and ferroelectric properties were studied as a function of the relative ratio between the two ceramics. It is found that all samples calcined at 800°C and sintered at 1050°C consist of Bi1.3Yb0.7O3 and Yb2O3 phases, which shows relatively high density. The highest relative density (ρ = 99.8%) and shrinkage (α = 13%) of BY-BT ceramics is obtained at x = 0.05. The maximum value of the remanent polarization (Pr) (Prmax = 0.1286 μC/cm2) can be obtained when x = 0.1. These results indicate a possible treat method to optimize the properties of two solid solutions.

Influences of La on Optical and Electric Properties of BiFeO 3 Thin Films

Bismuth ferrite (BiFeO3, short for BFO) is an important room-temperature single phase multiferroic materials. To further improve electric properties of BFO, La3+ was introduced. Bi1−xLa x FeO3 (x = 0–0.12) thin films were fabricated by sol-gel method. The microstructure, optical and electric properties of Bi1−xLa x FeO3 thin films have been investigated. XRD results show that Bi1−xLa x FeO3 thin films is rhombohedral distortion perovskite structure and the addition of La3+ can inhibit the formation of impure phase. The substitution of La3+ for Bi3+ on A sites can restrain the growth of grain and improve the roughness of thin films. The band gap of Bi1−xLa x FeO3 thin films is less than that of BFO thin films, and its band gap decreases first and then increases as the content of La3+ increases, which results from both Burstein-Moss effect and impurity level. A larger amount of La3+ (x = 0.12) can make leakage current of BFO thin films obviously decrease. Moreover, the remnant polarization and coercive electric field of Bi1−xLa x FeO3 thin films increase with the increasing of La3+ content. It results from the decrease of oxygen vacancy and effects of grain size.

Microstructural Regulation and Optical Performance of Bismuth Ferrite Nanowires by Precipitant

Bismuth ferrite (BiFeO3, short for BFO) is a single-phase and multi-ferrous material with ferroelectricity and weak ferromagnetism at room temperature. One-dimensional nanomaterials have specific physical properties due to anisotropy and unique size effects. In this paper, bismuth ferrite nanowires were prepared by hydrothermal method. The effects of precipitant (NH3·H2O, NaOH) on the microstructures of bismuth ferrite nanowires were studied. The results show that NaOH is a precipitant to promote the formation of nanowires, and the single crystal nanowires can be obtained using NaOH precipitation agent. The nanowires are arranged in the same direction. The diameter is less than 45 nm and the length changes from several tens nm to several microns. The absorption of nanowires is stronger than that of nanoparticles at wavelength of 230–400 nm.

Microstructure and Electric Properties of (Sr 1− x Ca x ) 3 Sn 2 O 7 Ceramics with Ruddlesden-Popper Structure

(Sr1−xCa x )3Sn2O7 (x = 0, 0.1 and 0.2) ceramics were prepared by conventional solid solution method. The microstructure, dielectric and ferroelectric properties of (Sr1−xCa x )3Sn2O7 ceramics have been investigated systematically. The XRD results show that (Sr1−xCa x )3Sn2O7 ceramics is orthorhombic structure and the lattice constants decrease as Ca2+ content increases. The grain size of (Sr1−xCa x )3Sn2O7 ceramics decreases with the increasing of Ca2+ content, which results in the decrease of dielectric constant and dielectric loss. The compactness of (Sr1−xCa x )3Sn2O7 ceramics deteriorates as Ca2+ content increases, which causes the increase of leakage current density. Moreover, the introduction of Ca2+ in (Sr1−xCa x )3Sn2O7 ceramics leads to the increase of the remnant polarization. But the remnant polarization changes a little with Ca2+ content when x is above 0.1. The coercive field increases with the increasing of Ca2+ content.

Sol-Gel Synthesis and Characterization of (1–x–y)BiYbO3-xLiNbO3-yBaTiO3 Ceramics

ABSTRACT (1–x–y)BiYbO3-xLiNbO3-yBaTiO3 (short form (1–x–y)BY-xLN-yBT) (x=0.1, 0.2, 0.3; y=0.8, 0.7, 0.6, 0.5, corresponding to BY-1LN-8BT, BY-2LN-7BT, BY-1LN-7BT, BY-2LN-6BT, and BY-3LN-5BT) lead-free ferroelectric ceramics were synthesized by sol-gel method. All of BY-LN-BT ceramics were firstly calcined at 800°C for 4 h and then sintered at 1200°C for 2 h. The microstructure, dielectric and ferroelectric properties of the samples were investigated. X-ray diffraction revealed that all the calcined BY-LN-BT powders are of pure single-phase rhombohedral structure. The main phase of all ceramic samples is perovskite structure, and Yb2Ti2O7 pyrochlore phase as the second phase coexists in BY-LN-BT ceramics except for BY-1LN-8BT. The relative densities of BY-LN-BT ceramics decrease with increasing LN content. All ceramic samples consist of well-faceted polyhedral grains, which show non-uniform shape, size and relative compactness. Addition of BT can increase the dielectric constant and promote frequency stability of dielectric properties. The highest relative permittivity is 4480 for BY-1LN- 8BT. The remnant polarization (Pr) and the coercive field (Ec) of BY-LN-BT ceramics decrease with decreasing frequency. The maximum values of Pr (1.706 μC.cm–2) and Ec (956.2V.mm–1) are obtained for BY-3LN-5BT, but its leakage current is very high. The best comprehensive electrical properties are obtained for BY-1LN-8BT ceramics. GRAPHICAL ABSTRACT

Anomalous Hall effect based on Pt/Bi0.9La0.1FeO3 bilayers

A 2.5-nm-thick platinum film with the shape of a Hall bar was deposited by magnetron sputtering on weak ferromagnetic rhombohedral and tetragonal Bi0.9La0.1FeO3 thin films. An anomalous Hall effect (AHE) was observed and studied as a function of magnetic field (H) and temperature (T). For the two samples, besides the obvious difference in the anomalous Hall resistance, the anomalous Hall resistance increases sharply with decreasing temperature, and even changes sign, thus violating the conventional expression. This observation indicates strong proximity effects and local-field-induced magnetic ordering in Pt on weak ferromagnetic thin films of rhombohedral and tetragonal Bi0.9La0.1FeO3 and their contribution to the spin-related measurements should not be neglected.

Effects of annealing temperature and template diameter on the microstructures of BiFeO3 nanowires

ABSTRACT Bismuth ferrite (BFO) nanowires were prepared by anodic aluminum oxide templates with different diameters and at different annealing temperatures. It is found that the annealing temperature and the template diameter affect crystal structure and surface topography of BFO nanowires. X-ray diffraction results show that all nanowires correspond to rhombohedral distorted perovskite structure. It can be observed from scanning electron microscope that the diameters of nanowires are in the range of 80 to 100 nm. And there are a large number of nanowires lining regularly. The nanowires of ‘Y’ model are discovered by transmission electron microscopy. SAED image reveals BFO nanowires coincide with the polycrystalline nature.