Advanced Materials Research Vols. 105-106

Abstract: Bismuth ferrite, BiFeO3, was an important multiferroic material, which simultaneously exhibited ferroelectric ordering and antiferromagnetic ordering in the bulk form. The solid solutions of Bi0.9Y0.1FeO3 with PbTiO3 were prepared by the conventional solid state reaction. It was clear that in Bi0.9Y0.1FeO3-PbTiO3 solid solution, the structure remined rhobohedral for 85 mole% of Bi0.9Y0.1FeO3, from 80 to 70mole% it were rhobohedral and tetragonal, and below 65 mole%, the structure transformed to tetragonal. The dielectric and ferroelectric properties of the ceramics had been significantly improved by means of ionic substitution of Ti4+ for Fe3+, which reduced the electric conductivity. The dielectric constants of the ceramic samples were enhanced from 84 to 241 and the remnant polarizations were improved from 0.494 to 2.17 μC/cm2.

Abstract: BaTiO3 thin film was prepared by the self-assembled monolayers technique and liquid phase deposition. The effects of pH values and the deposition temperature on the formation of BaTiO3 film were studied. The results showed that the Si substrate was in the precursor solution with 0.025mol/L (AHFT/BN/BA=1:1:3) and pH= 1.5. At 45°C deposited for 8h and annealed at 600°C for 2h, the BaTiO3 film with higher crystalline was prepared on the functionalized Si substrate. XRD and SEM tests showed that the film deposited in the precursor solution with different pH values appeared BaTiO3 characteristic peaks on the surface of every crystal. As pH values increased to 1.5 from 0.5, the strength of the film diffraction peak increased. But the width of the peak became smaller and the crystalline increased. When pH value was 2, due to the self-polymerized deposition of [Ti(OH)6]2-, it was easy to form the larger particles on the substrate. When the deposition temperature was 45°C, the acicular BaTiO3 film formed with the regular order and homogeneous planeness on the substrate. When the deposition temperature was between 55°C and 60°C, the dewatering and polymerizing speed between [Ti(OH)6]2- ions was higher than that between [Ti(OH)6]2- and -OH. The adsorption of the film to the Si substrate was weakened. It was easy for the film to fall off.

Abstract: In this article, (NH4)2TiF6, SrNO3 and H3BO3 were used as raw materials to prepare the precursor solution with the ratio of AHFT/SN/BA=1:1:3. The thin films of SrTiO3 were fabricated on the functional silicon substrates (100) by self-assembled monolayers (SAMs) with the liquid phase deposition (LPD). This article also studied the effects of wet state and the deposition temperature of the precursor solution before and after the functionalization of silicon substrate on the thin film growth. The results indicated that after the immersion in OTS for 30min, the surface contact angle of the silicon substrate changed from 24.64° to 100.91°. The substrate appeared hydrophobic property and it was irradiated by UV light for 30min. Then the surface contact angle of the substrate decreased to 5.00°. The substrate appeared hydrophilicity. The concentration of the precursor solution was 0.025 mol/L, the deposition temperature was 40°C and the deposition time was 9h, which were all helpful to SrTiO3 crystallization. XRD and SEM were used to characterize the physical phase of thin film and surface morphology at 600 °C with annealing and heat retaining for 2h. The results indicated that the thin film prepared by the mono-crystal Si substrate was SrTiO3 thin film with better crystalline. On the crystal surfaces of (110), (100), (200) and (211), there appeared the obvious diffraction peaks. The SrTiO3 grains on the surface had the clear outline and were regular and long columnar crystals.

Abstract: The CaCu3Ti4O12 samples with slight amount of doped bismuth were prepared and tested in this research. No second phase with bismuth was found in the doped samples. It was inferred that the bismuth ions has entered the lattice and take the place of the calcium ions. The grain size was diminished with the increase of the bismuth content. The bismuth atoms can inhibit the grains from growing large, and it could be used to modify the microstructure of CaCu3Ti4O12 ceramic. The reduction of the grain size resulted in the decrease of the relative dielectric constant, according to the “internal barrier layer capacitance (IBLC)” theory. The impedance measurements showed that the doped samples have less conductivity and lower potential barrier at the grain boundaries, and the substitution of the bismuth ions on the calcium cites might be the reason for it. As a result of the lowered potential barrier, the non-ohmic I-V property of the CaCu3Ti4O12 ceramic almost disappears in the doped ones.

Abstract: In this study, a disk-shaped step-down piezoelectric transformer that consists of Mg:LN single crystals operating in the extensional vibration mode was proposed, and its characteristics wre investigated. This paper proposed the PT using ring/dot electrode which had an outer diameter of 22 mm, a narrow annular gap circle of 1.0 mm and a thickness of 1.0 mm. The transformer was poled along the thickness direction. The top surface was covered by two ring-shaped electrodes separated by a narrow annular gap, and the regions covered by the outer and inner ring electrodes serve as the output and input parts of the transformer, respectively. The bottom surface was fully covered with a gold electrode. Moreover, according to the physical equivalent circuit model of the latest invented vibration mode, PT of Mg:LN single crystals were fabricated and characterized. Finally, we investigated the gain under different load resistances and input voltage.

Abstract: Effects of amount of Ca on crystal structure, microstructure, ferroelectric properties, and dielectric properties of the CaxSr2-xBi4Ti5O18 (CSBTi-x) ferroelectric ceramics were investigated. The results show that single-phase layered perovskite ferroelectrics were obtained and no appreciable secondary phase was found.Ca-doping results in a notable enlargement of remnant polarization 2Pr. The 2Pr of CSBT-0.15 reaches a large value, the remnant polarization 2Pr and coercive field 2Ec were 18.1µC/cm2 and 120.2kV/cm, respectively. Dielectric constant and dielectric loss of CSBT-0.15 was also measured, showing dielectric constant εr=199~194 and dielectric loss tanδ=0.02~0.014 over the range of 100 kHz~1MHz, respectively.

Abstract: Bismuth ferrite powders were synthesized by a simple citric acid complexing co-precipitation method at much lower temperature of 600°C. The work studies the calcination temperature and molar ratio of Fe and Bi on the structure and morphology. The as-prepared BiFeO3 powder was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscope and Fourier transform infrared spectrophotometer. The result shows that the phase pure BiFeO3 powders with cubic morphology were prepared as the calcination temperature was 600°C and molar ratio of Fe and Bi was 1:1. The nanoparticles was uniform with the size of about 200nm.

Abstract: Polycrystalline BiFeO3 (BFO) thin films were grown via metal organic deposition method on OH-functionalized organic self-assembled monolayers (SAMs) on glass. The stable BiFeO3 precursor solutions were obtained by using iron nitrate and bismuth nitrate as raw materials, acetic acid and glycol as solvent and citric acid as chelating agent. Firstly, the preparation and functionalization of octadecyltrichlorosilane (OTS) self-assembled monolayers on the hydroxylated glass substrates was investigated. Water contact angle measurement and atomic force microscopy (AFM) confirmed the presence of a uniform, complete monolayer. After BiFeO3 was prepared on glass substrates, the film- forming and heat treatment processing of BiFeO3 films were studied. The BFO film was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectrograph (EDS). XRD pattern indicated that the grains of sample began to grow at 450 °C, and which was made up of BiFeO3 and some impure phase. With the increase of temperature, impure phase were disappeared and the intensity of diffraction peaks strengthened. Pure BiFeO3 phase were obtained at 500 °C ~ 600 °C. When the heat treatment temperature increased above 650 °C, the impure phase appeared. SEM showed that the BFO thin film possessed a dense microstructure on OH-functionalized SAMs.

Abstract: Ni-Zn spinel ferrite and Cu-doped spinel ferrite were prepared by a conventional ceramic processing method. Microwave absorption, complex permittivity and permeability of the (Ni0.5Zn0.5)Fe2O4 and (Ni0.4Cu0.2Zn0.4)Fe2O4 spinel ferrites within the frequency range of 0.5-18 GHz were investigated. The reflection loss calculation results show that the Ni-Zn spinel ferrite and Cu-doped Ni-Zn spinel ferrite are good electromagnetic wave absorbers in the microwave range. The single layer (Ni0.4Cu0.2Zn0.4)Fe2O4 spinel ferrite absorber with a thickness of 9.2 mm achieved a reflection loss below -10 dB (90% absorption) at 0.5-2.3 GHz, and the minimum value is -35.63 dB at 1.1 GHz. When the first layer and second layer are (Ni0.5Zn0.5)Fe2O4 and (Ni0.4Cu0.2Zn0.4)Fe2O4 spinel ferrites respectively, the laminated absorbers with double spinel ferrite layers with a thickness of 3 mm achieved a reflection loss below -10 dB at 9.9-12.3 GHz, and the minimum value is -35.3 dB at 11.7 GHz.

Abstract: This article used PTCS to dispose the self-assembled substrate, and prepared the precursor by the ratio of AHFT / SN / BA = 1:1:3 and then immersed the functionalized substrate into the precursor supersaturated solution. With the colloidal particles absorption induced by SAMs, SrTiO3 thin film was prepared by the self-assembled monolayers with liquid phase deposition method. The effects of the time of UV radiation and the time of PTCS immersion on the substrate contact angle were studied and the time of UV radiation had an effect on the substrate functionalization after PTCS immersion. The results showed that the first UV radiation for 25 min, PTCS immersion for 7 min and the second UV radiation for 30 min were beneficial to the crystallization of SrTiO3. XRD and AFM were used to characterize the thin film physical phase and surface morphology at 600oCwith annealing and heat retaining for 2 hours. The results also showed that under the same condition, the SrTiO3 crystals on the thin film surface had the clear outline and the spherical crystals were distributed regularly and evenly.