Materials Science Forum Vol. 848

Abstract: Al-Si-Mg alloys, an important aluminum cast alloys, are excessively used inmanufacturing of critical components due to their high strength to weight ratio, flexibility ofmanufacturing designs, economic processing and capital material cost for automotive industry. Thisresearch is aimed to study microstructure evolution including distribution and morphology ofiron-rich intermetallic, as well as eutectic Si accumulation and their effect on mechanical propertiesof Al-Si-Mg (A356) casting alloy after artificial ageing. The results show that formation of iron-richintermetallic and eutectic Si accumulation resulted in surprisingly opposite mechanical properties,especially ductility. The elongations deceased with increase of area of accumulated eutectic Si and theamount of needle-like iron-rich intermetallic. When the area of accumulated eutectic Si reached 31%of the microstructure of the A356 alloy, the strength and elongation were respectively damaged to129.69 MPa and 1.05%. Moreover, the amount of needle-like iron-rich intermetallic increased, thestrength and elongation respectively decreased.

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: Soft magnetic Fe-B-P ultrafine particles with amorphous structure were prepared by aqueous reduction method with variable pH values. The microstructure, compositions and the soft magnetic properties of Fe-B-P submicron particles were investigated by using field emission scanning electron microscope (FE-SEM), X-Ray Diffraction (XRD), mössbauer spectrum (MS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), vibrating sample magnetometer (VSM). The results showed that a series of Fe-B-P amorphous particles with the average particle size of 0.26~0.42 μm were obtained depending on the pH value of solution. As pH value increased, the contents of B and P increased, and the specific saturation magnetization of the Fe-B-P submicron particles decreased. Some electrons, transferred from p-shell of B atoms and P atoms to 3d-shell of Fe atom, resulted in the decrease of the number of unpaired electron, which in turn led to reduction of the average hyperfine magnetic field of the Fe-B-P particles and the decrease of the magnetic torque of Fe atoms. The relation between hyperfine magnetic field (H_hf) and the specific saturation magnetization was in accord with the Marshall’s equation. At the same time, the enhancement of the shielding effect on 4s electron orbital, i.e., the density of 4s electron reduced, leading to the increase of Isomer Shift.

Abstract: FeSe superconducting bulks were prepared with high energy ball milling (HEBM) aided sintering process, within which process, tetragonal β-FeSe superconducting phase could be formed directly with one step sintering process, and the formation of hexagonal δ-FeSe non-superconducting phase was effectively avoided. The influences of HEBM time on the sintering process of FeSe bulks were systematically investigated. With different HEBM time, the phase composition and morphology of precursor powders changed correspondingly, which thus influenced the final phase composition and superconducting properties of FeSe superconducting bulks. Due to the formation of FeSe bulks with larger tetragonal phase content and higher superconducting transition temperature, HEBM time of 6.0 h was recognized as the optimal parameter. Shorter HEBM time could lead to the insufficient decrease of particle size and low density. While longer HEBM time caused the formation of amorphous hexagonal δ-FeSe, which crystallized during sintering process. Thus no more tetragonal FeSe could be obtained. The FeSe superconducting bulk with the critical temperature T_c(onset) of 8.0 K was obtained with the HEBM time of 6 h, and sintering temperature of 700 ^oC for 12 h.

Abstract: Several Bi-O-S compounds with nominal composition of Bi₄O₄S₃, Bi₃O₂S₃, Bi₂OS₂ have successfully been synthesized. The superconducting properties present to be similar with each other for Bi₄O₄S₃ and Bi₂OS₂ compounds, but much better than the Bi₃O₂S₃ compound. The former two possess a zero resistance temperature at 4.1 K, whereas the latter one is 3.7 K. Two diamagnetic transitions have been observed in the M-T curve for all three compounds. The starting nominal composition definitely affects the superconductivity of the final products.

Abstract: YBa₂Cu₃O_7-δ (YBCO) coated conductors have wide-ranging potential in large scale applications, such as, superconducting maglev trains and superconducting electric cables, but low current carrying capability restrains the practical application of YBCO coated conductors at high temperatures and high magnetic fields. It is crucial to develop YBCO coated conductors with high flux pinning capability. In this paper, epitaxial, dense, smooth and crack-free YDy_xBa₂Cu₃O_7-δ (x = 0~0.5) films were prepared on a LaAlO₃ (LAO) single crystal substrate via a fluorine-free polymer-assisted metal organic deposition (PA-MOD) method. The effects of Dy addition on the microstructure and superconducting character of YBCO films were investigated. The all films show a strong c-axis orientation and good texture in-plane and out of plane. The Dy addition to the YBCO film hardly affects the critical temperature of YBCO superconductor. The irreversibility fields of YBCO films can be improved with the Dy addition x = 0.5 compared to the pure YBCO film but decreased in the x = 0.3 sample.

Abstract: The giant converse magnetoelectric coupling (GME) was observed in the multiferroic Co₄₀Fe₄₀B₂₀/(011)-0.7Pb (Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ heterostructures at room temperature in this investigation. A tunability of magnetization by electric field along the [100] direction was up to-66.7% at-10 Oe bias magnetic fields. Moreover, the non-volatile magnetization switching was found after removal of bipolar electric field. The corresponding remanent magnetic states even without the assistance of bias magnetic fields were stable and could be modulated synchronously by a sequence of pulse electric fields. The 90^o rotation of easy axis and non-symmetrical ferroelastic domain switching contributed to the above results. This work is of great significance in designing ultra-low power and non-volatile magnetoelectric memories and other spintronic devices at room temperature.

Abstract: A study of the structural and magnetic properties of Cr-and Fe-doped CeO₂ nanoparticles produced by the sol–gel-based method was undertaken. The crystal structure and phase, morphology, and magnetic properties of the sample were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (Raman) and physical property measurement system (PPMS). XRD and Raman studied showed that Cr-and Fe-doped did not change CeO₂ original cubic fluorite crystal structure, and no ferromagnetic secondary phase was observed. SEM images showed that Cr-and Fe-doped CeO₂ nanoparticles were spherical, uniform size, and good dispersion. The particle size was about 20 nm. The magnetic measurements showed that the Cr-and Fe-doped CeO₂ nanoparticles presented ferromagnetic behavior at 10 and 300 K, indicating the Curie temperature was above room temperature. The magnetization diminished with the increase of the temperature. The saturation magnetization and coercivity of Fe-doped CeO₂ nanoparticles were higher than that of Cr-doped CeO₂ nanoparticles. Combined with the results of XRD and Raman, the ferromagnetic behavior can be attributed to the intrinsic properties of Cr-and Fe-doped CeO₂ nanostructures.

Abstract: The bonds structure, atomic coordination situation and local cluster structure in SrBi₂Ta₂O₉ were analyzed by means of the Atomic Environment Calculation (AEC), and then the SrBi₂Ta₂O₉ crystal was decomposed into 20 pseudo-binary crystals with the crystal decomposition method. The chemical bonds properties, such as effective valence electron density and iconicity of the individual bond were calculated by the dielectric chemical bonds theory. And the correlation between chemical bonds properties and spontaneous polarization of the bismuth layered ferroelectrics was established. Finally, the spontaneous polarization in ferroelectric SrBi₂Ta₂O₉ and other relevant ferroelectrics were calculated, which are in good agreement with the experimental values and other theoretical calculated values.

Abstract: Pass through flux (PTF) is an essential parameter for the magnetron sputtering process of ferromagnetic materials. In the present investigation the influence of deformation, recrystallized microstructure and thickness on PTF of Ni was examined by the analysis of microstructure and hardness of high purity Ni. The experimental results showed that PTF of rolled Ni increased significantly comparing to the annealing microstructure that is related to the dislocation and stress of microstructure. With the recrystallization and grain growth of deformed samples, PTF decreased to be about 30%. PTF was also associated with the thickness of material. It increased by 6% when the thickness of 0.5mm decreased. This research is useful to guide and improve the design, development and preparation of magnetic sputtering materials.