Papers by Keyword: Ferroelectricity

Abstract: We investigate the physical and electrical characteristics of the Al-doped or undoped HfO₂/SiO₂ gate stacks on 4H-SiC by testing MOSCAP chips fabricated in house. A clear reduction in accumulation capacitance (C_ox) with increasing chuck temperature from room temperature up to 523 K is observed, with Al-doping playing a key role and aligning with temperature-dependent Landau ferroelectric theory. Chips annealed at 1100°C in N₂ ambient show the highest C_ox decrease rates while maintaining functional MOS interfaces with acceptable flatband voltage, hysteresis, and Dit profiles. TCAD simulations on a double trench MOSFET model, based on the extracted data indicate improved electro-thermal performance, demonstrating that Al-doped HfO₂/SiO₂ gate stacks are a promising approach for enhancing 4H-SiC power devices.

Abstract: High-quality BFCO films with smooth morphology were deposited on (001)-oriented single crystal substrates by pulsed-laser deposition. The perfect ferroelectric nature of the BFCO films were probed by PFM and electrical P-E hysteresis measurements and the obtained saturated remeanent polarization value reaches up to 60 μC/cm². Besides, BFCO films show relatively low bandgap of 2.5 eV, can absorb the sunlight and convert the solar energy to electrically energy effectively. A photocurrent of 1.2 mA/cm² and an open-circuit voltage of about 0.53 V were obtained under AM1.5G illumination. The results mainfest the BFCO a potiential material for multifunctional devices, especially for photovoltaics.

Abstract: It is expected that BiFeO₃-based materials will have both ferroelectricity and ferromagnetism. (1-y)BiFe_(1-x)Mn_xO₃-yBaTiO₃ system was prepared using solid state reaction method. The goal of this study is to uncover the impacts of Mn doping and BaTiO₃ content on the crystal structure, magnetism and ferroelectric properties. By forming a solid solution with BaTiO₃, stable perovskite BiFeO₃ was achieved. The rhombohedrally distorted (1-y)BiFe_(1-x)Mn_xO₃-yBaTiO₃ showed weak ferromagnetism due to the composition of BaTiO₃ and the doping of Mn ion. 0.8BiFe_0.9Mn_0.1O₃-0.2BaTiO₃ and 0.7BiFe_0.9Mn_0.1O₃-0.3BaTiO₃ ceramics exhibited typical P-E hysteresis loops.

Abstract: Croconic acid is the first single molecular organic ferroelectric material exhibiting very high spontaneous polarization (~ 20 μC/cm²) at room temperature. Maximizing polarization depends on minimizing void defects in croconic acid crystals. In this experiment, the change in void defects upon the thermal treatment is characterized using positron annihilation lifetime spectroscopy. Both defect void size and intensity are measured, and their dependence upon the thermal treatment duration is studied. In addition, the relation between the void defect and ferroelectric hysteresis of croconic acid is established.

Abstract: (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ (NBBT) ceramics doped with 0.1∼2.0 mol.% Ba (Zr_0.05Ti_0.95)O₃ were investigated in terms of the sintering, microstructure, phase transition, and piezoelectric properties. BZT doping has no remarkable effect on the microstructure and densification within the studied doping content. Up to 2 mol.% BZT can dissolve into the lattice of NBBT ceramics, and the structure symmetry is not changed. However, a significant change in the piezoelectric properties took place. The piezoelectric coefficient d₃₃ for the 0.1 wt.% BZT-doped NBBT ceramics sintered at 1150 °C was found to be 120 pC/N and the electromechanical coupling factor k_p = 0.24.

Abstract: The lanthanum-modified lead zirconate titanate transparent ceramics with different Zr/Ti ratio were prepared by the hot pressing sintering method. A single perovskive structure with a dense microsctructure was obtained and the transgranular fracture of PLZT ceramics tended to be more serious As the Zr/Ti ratio increases, the transmittance of PLZT ceramics tended to be higher and the transgranular fracture became more serious. The P-E loops changed froe a square hysteresis loop to a double tending slim hysteresis loop. Besides,the S-E loops changed from a approximate parabolic shape to a butterfly shape. These two loops confirm the transition from normal ferroelectric to anti ferroelectric phase occured with the Zr/Ti ratio increasing.

Abstract: We studied the effect of annealing and Co ion doping on the structure, leakage current, ferroelectric polarization and magnetism of BiFeO₃ samples. X-ray diffraction patterns demonstrate that an appropriate Co doping concentration is favor of suppressing the secondary phase but annealing treatment is apt to the growth of both the main and the secondary phases. The current density as a function of an electric field indicates that Co doping increases the leakage current density as samples before annealing but suppresses it after annealing. Annealing treatment improves the leakage for Co-doped sample and reduces it for the undoped sample. Ferroelectric hysteresis loops reflect that Co ions doping is liable to increase the ferroelectric polarization, while the sample is annealed it will do opposite effect. However the annealing treatment do improve the ferroelectricity for pure BiFeO₃ sample. The magnetic hysteresis at room temperature shows the obvious enhancement of ferromagnetic properties with the sample after annealing.

Abstract: Bi_1-xLa_xFeO₃(x=0, 0.3) thin films were deposited on glass/ITO substrates through Sol-Gel Dip-Coating method and rapid annealing process. The structures were detected by X-ray diffraction patterns, Raman spectrometer and scanning electron microscopy. The magnetic, ferroelectric and optical properties of the films were studied by vibrating sample magnetometer, ferroelectric integrate tester and photovoltaic performance testing system, respectively. The experimental results indicate that BiFeO₃ thin film presents rhombohedral perovskite structure and Bi_0.7La_0.3FeO₃ films showed distorted perovskite structure, which were confirmed by XRD patterns and Raman spectrometer. The magnetism and ferroelectric properties of the films were obviously enhanced by La doping. Furthermore, the photocurrent response and photovltaic effect in BLFO thin films were detected.

Abstract: Lead lanthanum zirconate titanate (PLZT) transparent ceramics have attracted more and more attentions for their unique electric-induced light scattering effects. The PLZT ceramics of 7.45 mole% lanthanum with different Zr/Ti ratios (Zr/Ti=68/32, 69/31, 70/30, 71/29, 72/28) were prepared by the hot-press sintering method. The X-ray diffraction patterns confirm that all the PLZT samples are perovskite structure without detected secondary phases. The SEM images of the fracture surfaces of the samples show that all the PLZT materials tend to fracture transgranularly, and exhibit fully dense and uniform microstructures. All the samples with different Zr/Ti ratios present typical relaxation ferroelectric phase transition characteristics with square shaped hysteresis loops. Noticeably, all the original PLZT samples show an excellent transparency in the wavelength range from visible to near-infrared, and they will become opaque after an appropriate electric field experienced. The opaque sample can also recover to the transparent state when an inverse compatible electric field acts on it. The contrast ratio of the sample increases firstly and then decreases when the Zr/Ti ratio increases from 68/32 to 72/28 (λ=632.8nm). The PLZT (7.45/70/30) material shows a maximum contrast ratio, which makes it promising to apply in optical modulators.

Abstract: The goal of this study was to investigate the origin of ferroelectricity in Bi₄Ti₃O₁₂. The bismuth titanate Bi₄Ti₃O₁₂ (BTO), which belongs to the Aurivillius family, is one of the most interesting compounds among the bismuth-based layered ceramics. BTO is a ferroelectric material with wide applications in the electronic industry, as capacitors, transducers, memory devices and sensors. Aurivillius structures are described with a general formula following form:A_m-1Bi₂B_mO_3m-1. BTO ceramic materials is an Aurivillius structure with m = 3. This ceramic materials were prepared by conventional mixed-oxide method of the solid state reaction. The temperature of the Bi₄Ti₃O₁₂ sintering was selected on basis of thermogravimetric studies. The crystal structure of Bi₄Ti₃O₁₂ was examined at room temperature with an X-ray diffraction method. Phase formation behavior was investigated using the differential thermal analysis (DTA) and the thermal gravimetric (TG). The microstructure was investigated by SEM method. Based on the Dorrian’s model, the value of displacements between bismuth ions and oxygen octahedra was calculated.