Materials Science Forum Vol. 815

Abstract: The influence of dislocation density on micromechanical characteristics of Cu₆Sn₅ and Cu₃Sn was studied by nanoindentation. The dislocation density dependent hardness of Cu₆Sn₅ and Cu₃Sn was quantitative analyzed. High dislocation density increased the critical shear stress corresponding to the first pop-in events and induced micro plastic deformation before the first pop-in events. For Cu₆Sn₅, dislocation creep and lattice diffusion dominate the high stress regime (HSR) and the low stress regime (LSR), respectively, regardless of the dislocation density. High dislocation density increases the stress exponent (n) of HSR, but decrease n of LSR. Dislocation motion is the dominate creep mechanism of unstrained Cu₃Sn. After pre strain, the creep behavior of Cu₃Sn was divided into HSR and LSR. But dislocation motion is still the dominate creep mechanism. Potential mechanism of the dislocation density dependent micromechanical characteristics was explained based on our experimental results.

Abstract: (Sr_1-xBa_x) ₂(Nb_0.9Ta_0.1) ₂O₇ (SBNT) ceramics were prepared by solid state reaction. The crystal structure of SBNT ceramics, surface morphology and dielectric properties were studied using XRD, SEM and LCR instrument analyzer, respectively. The results show that the grain size decreases with increasing Ba concentration, and all samples show single phase, no second phase can been observed. Addition of Ba ion can improve the dielectric properties of SBN ceramics. The dielectric constant increases first, then decreases; the maximum value (ε_r=97) can be obtained at x=0.1, the dielectric constant changes slightly with increasing wide frequency.

Abstract: The effect of Ag content on the morphology of the intermetallic compound (IMC) layer at the interface between Sn-xAg-0.7Cu (x=0.0 wt.%, 0.3 wt.%, 0.8 wt.%, 3.0 wt.%) and Cu substrate has been investigated. After reflow, the slight addition of Ag element can suppress the growth of IMC. However, as the Ag content increases, the thickness of IMC is enhanced. After aging at 150°C, the IMC growth rate constant decreases with the addition of Ag. The IMC growth rate constant of Sn-3.0Ag-0.7Cu is 0.94864×10^-5 μm²/s, which is the lowest among these solders. As the Ag addition is 0.8wt% and 3.0wt%, the Cu₃Sn growth rate constant is 0.16641×10^-5 μm²/s and 0.18496×10^-5μm²/s, compared to the Sn-0.7Cu solder decreased 54% and 49%, respectively. As a result, the addition of Ag element improves the anti-aging properties and suppresses the growth of Cu₃Sn layer, which leads to the improvement of solder joint reliability.

Abstract: Bismuth ferrite is an important material in ferroelectric photovoltaic field, because of its narrow band gap and large polarization. Doping is a common method to further improve the photovoltaic properties of bismuth ferrite. Mn-doped bismuth ferrite thin films were prepared by sol-gel method. The effects of manganese on the crystal structure, ferroelectric and photovoltaic properties have been investigated. The result indicates that Mn-doped bismuth ferrite thin films are single phase and the lattice constant increases with the increase of manganese content. As manganese content increases, the remnant polarization and coercive electric field increase, while the short circuit photocurrent density and power conversion efficiency decrease. The open circuit photovoltage increases first and reaches the maximum and then decreases as manganese content increases. The results indicate that enhanced ferroelectricity caused by addition of manganese doesn’t make improvement on the photovoltaic characteristic.

Abstract: Barium ferrite fibers and barium ferrite powders were successfully prepared respectively via Electrospinning method and sol-gel auto-combustion method by using Fe (NO₃)₃·9H₂O, Ba (NO₃)₂ as one of the main raw materials. X-ray diffraction (XRD) and field emission scanning electron microscope (FSEM) were used to study the phase composition and microstructure of barium ferrite. The results showed that barium ferrite fibers consist of a mixture of barium ferrite particles, the diameter of fibers is about 200 nm; barium ferrite powders prepared by sol-gel auto-combustion method were flake barium ferrite compositing of rod-like grains of less than 100 nm in size stacking disorderly. Magnetic properties were investigated by vibrating sample magnetometer (VSM), the results showed that the values of Mr, Ms, and Hc of barium ferrite fibers and powders are quite different due to their different morphologies.

Abstract: (Bi_1-xSm_x)(Fe_0.95Mn_0.05)O₃ (x=0.00, 0.03 and 0.06) thin films were deposited on the quartz substrates by sol-gel technique. The results of X-ray diffraction patterns indicated all thin films had rhombohedral perovskite structure. Moreover, the Sm and Mn co-doping at A-and B-site of BiFeO₃ resulted in the structural distortion. Scanning electron microscope measurements exhibited that the uniform surface morphology could be obtained by co-doping and the average grain size of the films decreased with increasing Sm content. Furthermore, the fundamental absorption edges of xBSFMO films showed a blue shift with the increase of Sm content which can be observed in transmittance spectra. The optical band gap of the thin films for x= 0.00, 0.03 and 0.06 can be expressed by (0.84x+2.62) eV, which is due to the Burstein-Moss effect.

Abstract: Bi_0.9Ba_0.1Fe_0.95O₃ and Bi_0.9Ba_0.1Fe_xTi_0.05O₃ (x=0.95, 0.925, 0.90) ceramics were prepared through conventional solid state reactions. X-ray diffraction analyses indicated that a high content of perovskite phase was obtained for all the four compositions. While the three (Ba,Ti)-codoped compositions all showed a higher resistivity than Bi_0.9Ba_0.1Fe_0.95O₃, and Bi_0.9Ba_0.1Fe_0.925Ti_0.05O₃ had the best electrical and dielectric properties among the three (Ba,Ti)-codoped compositions, including the largest dielectric constant, the smallest dielectric loss at low frequency range, and the highest electrical resistivity. Magnetic hysteresis loop measurement revealed that the four compositions had similarly enhanced magnetic properties. It is concluded that much attention should be paid to fine composition adjustment when multiple elements are co-doped to BiFeO₃ system.

Abstract: A new kind of multiferroic three-ply-structured nanoceramic composites consisting of nanosized alloy-based magnetostrictive (MS) and ferroelectric powders (FE) were fabricated successfully by a conventional solid state reaction in air or argon ambient in our previous investigation. But there are still some problems needed to be solved, for example, the magnetic aging and decrease of saturated magnetization phenomena occurred in samples are perhaps related to the harsh preparation conditions such as storage duration and sintering atmosphere and so forth. In this paper, we will review the characteristics of the novel nanocomposites by means of the microstructure and magnetism existed in the samples with nanosized MS powders (i.e. (Tb_0.3Dy_0.7)_0.75Pr_0.25Fe_1.55, Sm_0.88Nd_0.12Fe_1.93) as fillers. Also, we hope some reasonable explanations and deeper understandings can be concluded about the proposed ageing and magnetism reduction exhibited when the samples were subjected to co-firing in air or argon ambient. Finally, the potential improvement and multifunctional applications in the future are also suggested.

Abstract: La_0.67Sr_0.33MnO₃ (LSMO)/Pb_0.92La_0.08Zr_0.65Ti_0.35O₃ (PLZT) composite film was fabricated on a (001) LaAlO₃ (LAO) single crystal substrate by a sol-gel technique. The results from X-ray diffraction (XRD) indicated that LSMO and PLZT could grow successively on LAO substrate with (001) preferred orientation. The ferroelectric and ferromagnetic properties of LAO/LSMO/PLZT composite film were also investigated. The results showed that the remnant polarization P_r, and coercive field E_c of the composite film at room temperature were 36.38 μC/cm² and 512.43 kV/cm respectively. Moreover, the composite film exhibited significant ferromagnetic hysteresis loops and soft magnetic behavior at temperatures lower than 250 K.

Abstract: s. Yttium-substituted bismuth titanate (Bi_4-xY_xTi₃O₁₂, BYT) thin films were deposited on the (111)Pt/Ti/SiO₂(100) substrates by a modified Sol-Gel process and studied in this work in terms of ^Y3+-modified microstructure and phase development as well as ferroelectric properties. With the aid of the fist-principle, the position of Y³⁺ substitution for Bi³⁺ on the microstructure of BYT was studied.The phase change in the formation of BYT crystalline and the effect of Y³⁺ substitution for Bi³⁺ on the microstructure of BYT was studiedbyXRD. The results showed that the optimal properties of the obtained BYT ferroelectric thin films were x:0.6. The ferroelectric properties of the films were also investigated. When the Y-substituted content x was equal to 0.6, the remnant polarization was the largest. The remnant polarization 2Pr value was equal to 16.02μC/cm²and the coercive field Ec value was 88 kV/cm.