The modification of surface,size and shape of barium zirconate powder via salt flux

The “top-down” process via direct conversion of the micro (μm)-to-submicroscale (sub-μm) particle was applied in this work by using eutectic chloride salts to prepare BaZrO₃. The particle size at optimum condition could be decreased by more than 10 times from 2.1 ± 0.9 μm to 168 ± 23 nm without destroying the 1:1 of Ba:Zr stoichiometry. The uniform sub-μm-BaZrO₃ powder was sintered in order to obtain ~98% dense ceramic at 1400°C/10 h, which is significantly lower than the 1650°C in normal cases. The microwave dielectric constant, tan δ, and quality factor were also determined. Furthermore, this method also was applied to lead-free piezoelectric material in the 0.87BaTiO₃–0.13BaZrO₃–CaTiO₃ (0.87BT–0.13BZ–CT) system. The particle size of 0.87BT–0.13BZ–CT was reduced greatly from >10 µm to 2.8 ± 0.4 µm. It can be proved that salt flux dissolution method enables high-purity with uniform sub-micro/nanometer powder production in one step by using simple laboratory equipment and low-cost raw materials.     

CaTiO3 induced ferroelectric phase coexistence and low temperature dielectric relaxation in BaTiO3–BaZrO3 ceramics

The series of 0.86BaTiO₃–(0.14?x)BaZrO₃–xCaTiO₃ (abbreviated as BT–BZ–xCT) ceramics with 0.03 ≤ x ≤ 0.11 were studied to obtain high piezoelectric properties. Rietveld refinement analysis indicated that the BT–BZ–CT compositions follow a gradual rhombohedral (R) → orthorhombic (O) + R → O + tetragonal (T) → T phase transformation with increasing x. Clear evidence of the series of ferroelectric phase transitions was also found in the dielectric results. The R‐O and O‐T transition temperature shifted close to ambient temperature, while the Curie temperature slightly increased with increasing x. In addition to the dielectric loss peaks associated with the structural phase transitions, a broad low‐temperature dielectric loss peak was detected in the R phase at T = 90‐150 K. This dielectric relaxation was attributed to the domain wall freezing and fits well to the Vogel‐Fulcher model with activation energy E_a ≈ 60‐300 meV and freezing temperature T_VF ≈ 75‐140 K. High piezoelectric strain coefficient (d₃₃*) of about 1030 pm/V at 10 kV was achieved at x = 0.07, and a high Curie temperature (T_C) was maintained at about 375 K.     

Dielectric properties of nanocrystalline barium zirconate titanate synthesized by glycine-nitrate autocombustion

Abstract

Dielectric properties of nanocrystalline barium zirconate titanate (Ba(Zr_xTi_1-x)O₃; BZT for x?=?0.1 and 0.3) synthesized by glycine-nitrate autocombustion method were investigated in this study. The phase formation examined by TGA-DTA, XRD, FT-IR and Raman spectroscopy confirmed that high purity single-phase BZT with perovskite structure was obtained by using glycine-to-nitrate molar ratio of 2.2:4 and calcining in air at 1100?°C for 4?h. TEM analysis showed that BZT had agglomerate particles consisted of primary spherical nanocrystals with the size of 8-11?nm. The diffuse phase transition behavior of BZT ceramics increased with increasing Zr concentration and for x?=?0.3, the Curie temperature; T_c, shifted to below room temperature. The BZT ceramics for x?=?0.1 had relatively high dielectric constant (ε), 13007, low T_c, 76?°C and comparable dielectric loss (tan δ) at T_c, 0.012 which caused by the high degree of Zr diffuseness into the perovskite structure. These results suggest that glycine-nitrate autocombustion is the effective method for preparing high quality BZT ceramics.     

Key knowledge factors in Thai construction practice

This research has mainly focused on the practice of knowledge management in Thai construction projects at the on-site work level. The main objective was to identify whether or not knowledge factors influence on-site execution of works. A combination of qualitative and quantitative approaches was employed. The focus group interview with 16 construction managers was conducted to gather in-depth information related to practice of project knowledge management. This data was used to develop the questionnaire to explore key knowledge factors. The questionnaire was sent to 103 participants in 70 construction projects in Thailand. The survey data were analyzed by factor analytic techniques to identify key knowledge factors influencing on-site construction works. The findings showed that there were six key knowledge factors: (1) visionary leadership, (2) reward or incentive, (3) collaboration, (4) trust, (5) information technology, and (6) individual competency or skills.     

Aqueous Co-precipitated spherical shape PbZrO3 nanopowders: Perovskite phase formation

The perovskite phase formation of nanocrystalline powder of lead zirconate (PbZrO₃, PZ) was investigated. The structure, phase formation and morphology of PZ powders were characterized using the X-ray diffraction technique (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscope (TEM) and differential scanning calorimetry (DSC). Tetragonal zirconia (t-ZrO₂) phase was found as an intermediate phase during the calcinations process, followed by the crystallization of the orthorhombic PZ phase. The change in relative amount of the residual t-ZrO₂ phase as a function of calcination temperature was estimated from the relative intensities of selected Raman peaks. From a TEM photograph, the PbZrO₃ powder was found to be spherical in shape with uniform nanosized features. The average particle size for the calcined powders was about 10.44±1.21 nm.     

Strategic Assets Driving Organizational Capabilities of Thai Construction Firms

This research study aims to identify strategic assets which currently drive and enhance the organizational capabilities of construction firms. There were 258 sets of questionnaires assessing the level of importance given to 106 substantial resources underlying six organizational capabilities of Thai construction firms that were analyzed. Using factor analysis, these 106 items were reduced to 14, which were termed strategic assets. These 14 strategic assets were then classified based on their influence on the six organizational capabilities. The results indicate that Thai construction firms concentrate mostly on developing excellent reputation, creating strong bargaining power with suppliers and subcontractors, and strengthening the firm’s financial stability. However, they do not give much importance to effective risk and investment management, continuous development and innovation, and explicit strategic management. These findings provide in-depth insight to comprehensively understanding a Thai construction firm’s capabilities. These 14 strategic assets should thereafter be used to develop a practical tool for managers of construction firms to evaluate their firm’s strengths and weaknesses as well as to identify strategic assets required to enhance competitiveness in the market.     

Phase Formation,Microstructure, and Densification of Yttrium‐Doped Barium Zirconate Prepared by the Sonochemical Method

Spherical monodispersed yttrium‐doped barium zirconate (BaY_0.1Zr_0.9O₃; BYZ) particles were successfully prepared in single step without the requirement of calcination process by the sonochemical method in highly basic aqueous solution. The stoichiometric solution of BaCl₂.2H₂O, ZrOCl₂.8H₂O, and YCl₄.6H₂O was precipitated in a 20 M NaOH under high‐intensity ultrasonic irradiation (20 kHz, 150 W/cm²) for 15, 30, and 60 min. As‐prepared powders were identified by XRD, FT‐IR, and Raman spectroscopy as cubic perovskite BYZ. The microstructure examined by SEM and TEM showed spherical‐shaped BYZ particles formed by aggregation of primary nanocrystals, and this unique morphology was induced by the effects of the ultrasonication and the strong alkaline environment. BYZ powders prepared under ultrasonication for 60 min had narrow‐sized distribution with the average particle size of 267 ± 26 nm and the specific surface area of 40.2 m²/g. BYZ ceramics sintered in the air at 1550°C for 20 h showed good densification (95%) and consisted of large grain size (7.67 ± 2.79 μm).