Key Engineering Materials Vols. 675-676

Abstract: The ferroelectric ceramics with composition of (1-x)Pb(Zr_0.52Ti_0.48O₃ [PZT] – x(Ba_0.9Ca_0.1)(Ti_0.85Zr_0.15)O₃ [BCZT] (x = 0, 0.04, 0.08 and 0.10 ) have been successfully prepared via two-step mixed oxide method. The material systems of lead zirconate titanate (PZT) and barium calcium zirconate titanate (BCZT) have been intensive studied due to their remarkable properties of high ferroelectric and piezoelectric values. In this work, we are interesting to combine PZT with BCZT system in order to improve the electrical property of the ceramic samples. From the obtained results, it can be confirmed that ferroelectric values are significant increased with the optimum amount of the BCZT.

Abstract: The dependence of microstructure and mechanical properties of Sn-0.7wt.%Cu solder alloys on different cooling rates were investigated. Two cooling rates were employed during solidification: 0.04 °C/s (mold-cooled system) and 1.66 °C/s (water-cooled system). The results showed that the ultimate tensile strength of Sn-0.7wt.%Cu solder alloy increased but the elongation decreased when water-cooled system was used. The microstructure of Sn-0.7wt.%Cu solder alloys solidified by both cooling systems exhibited two phases of Sn-rich and Cu₆Sn₅ intermetallic compounds (IMC_s). However, finer grains were observed in the water-cooled specimens.

Abstract: The Y3-8-11 superconductors and silver composite superconductors were synthesized by solid state reaction. The standard four probes method was used to measure the critical temperature (T_c), and the XRD technique (FULLPROF PROGRAM) was used to determine the lattice parameters, space group and phase compositions. It was found that the pure Y3-8-11 has the lowest T_c onset about 95 K, and the more silver doped concentration, have the higher T_c offset and T_c onset. The samples have both superconducting phase and non-superconducting phase. The silver doped samples have higher superconducting phase. The Pmmm space group was corresponding as to superconducting phase. The non-superconducting phase exhibite in Y211 and BaCuO₂ with Pbnm and Im-3m, respectively. The surface of the silver doped sample is much smoother and denser compared to the undoped samples without impurities.

Abstract: Feroelectric lead lanthanum zirconate titanate (PLZT) ceramics 9/70/30 were synthesized by conventional mixed-oxide method via a vibro-milling technique. The effect of sintering temperature and two-stage sintering method on electrical properties of PLZT ceramics was investigated. The ceramic powder was uniaxially pressed in pellets and sintered at the temperatures ranging from 1200 to 1275 °C for 4hrs and two-stage sintering temperature at 1200 °C for 4 hrs. Dielectric, ferroelectric and strain properties of ceramics were characterized by LCR meter, modified Sawyer–Tower Circuit and modified Michelson interferometric technique respectively.

Abstract: In the present work, strontium iron niobate SrFe_0.5Nb_0.5O₃ ceramics doped with aluminum were synthesized by a solid-state reaction technique. Phase formation investigation by X-ray diffraction technique (XRD) revealed that all ceramics exhibited pure perovskite phase with orthorhombic symmetry. Grain size observed by electron microscopy (SEM) was found to increase with increasing sintering temperature. The electrical properties and related parameters of the ceramics were also measured. The ceramics exhibit very good dielectric behavior and have a significant potential for dielectric applications.

Abstract: Alumina/zirconia composite materials are widely used for biomedical applications because of their high biocompatibility and good mechanical properties. In this work, the effects of slurry solid content and binder type are studied on the characteristics of spray-dried composite particles. The tap density and particle size of composite particles increase while the compressibility index decreases with increasing solid content of slurry. An analysis of the SEM micrographs of spray-dried particles confirms the formation of dense composite particles of round shape without internal holes with 70 wt.% slurry using PVA+PEG co-binder.

Abstract: Zn-Al-O compounds were successfully synthesized via co-precipitation method at pH 8 followed by calcination process at 900 oC. Influence of different precursor (Zn:Al) ratio and calcination period on their structural properties and formation have been investigated. Varying Zn:Al ratio was conducted at 2:1, 1:1, 1:2 and 1:4 with different calcination time at 0, 2, 4, and 6 h. Phase transformation and morphologies were characterized by X-ray diffraction and field-emission scanning electron microscope. Moreover, chemical bonding of Zn-Al-O compound was analyzed by Raman spectroscopy. The results indicated that chemical bonding between Zn-Al oxide evidentially occurred in all samples in composite form and spinel structure. In addition, the amount of Al content considerably contributes to significant aggregation in zinc aluminate (ZnAl₂O₄) spinel crystalline phase affirmed by XRD result. Meanwhile, SEM images reveal high crystallinity and strong formation of the compound obtained by prolong calcined period.

Abstract: Zn-Sn-O powders were synthesized by simple co-precipitation method combined with calcination process using zinc chloride (ZnCl₂) and tin (IV) chloride pentrahydrate (SnCl₄–5H₂O) as starting precursors of Zn and Sn in aqueous solution. The effect of precursors ratio on phase structure of Zn-Sn-O compound was investigated by varying ratio of Zn:Sn in the co-precipitation system. For the effect of calcination temperature, the as-precipitated product obtained at Zn:Sn ratio of 1:1 was calcined at different temperatures (400-900 °C) to study phase transformation. Structural properties of as-precipitated and after-calcined powders were characterized by X-ray diffraction (XRD) while surface morphologies of final products were observed by scanning electron microscope (SEM), and thermogravimetric analysis (TGA) was used to study their thermal properties. The results indicate that the XRD pattern of Zn-Sn-O powders obtained at ratio of Zn greater than Sn can be assigned to mixed phase of ZnO and Zn₂SnO₄. On the other hand the XRD patterns of products obtained at ratio of Sn greater than Zn confirm a mixture of SnO₂ and Zn₂SnO₄. For the effect of calcination temperature, the rarely spinel phase of Zn₂SnO₄ begin occur with mixed phase of ZnO and SnO₂ at the calcination temperature of 600 °C and pure spinel structure can be obtained at the temperature above 900 °C.

Abstract: The properties of modified Bi_0.5Na_0.5TiO₃ (BNT) based lead-free ceramics were investigated. The BNT-based ceramics were prepared by a two-steps sintering method. The ceramics were sintered at T₁=1373 K and T₂= 1173 K for various dwell times (0, 2, 4, and 8h). The properties of the ceramics were characterized by many techniques. The ceramic samples exhibited a pure perovskite phase with rhombohedral symmetry. The microstructural analysis by a scanning electron microscopy (SEM), indicated that all ceramics had a similar microstructure. Piezoelectric and mechanical properties of the ceramics were improved at a suitable dwell time at T₂.

Abstract: Ba (Fe_0.8Ga_0.2)_0.5Nb_0.5O₃ ceramics were synthesized via a solid state reaction method. The Raman spectrum analysis indicated that the sample presented a cubic structure. Dielectric measurement on the ceramics with Ag-paste and Au-sputtered electrodes showed that all ceramic samples exhibited very high dielectric constants with a strong frequency dispersion. The Au-sputtered electrode samples presented higher dielectric tunability the dielectric constant than Ag-paste electrode samples.This behaviour was related with the electrode effect, occured in the studied samples.