Tawee Tunkasiri

Perovskite phase formation and ferroelectric properties of the lead nickel niobate-lead zinc niobate-lead zirconate titanate ternary system

The ternary system of lead nickel niobate Pb(Ni 1 / 3 Nb 2 / 3 )O 3 (PNN), lead zinc niobate Pb(Zn 1 / 3 Nb 2 / 3 )O 3 (PZN), and lead zirconate titanate Pb(Zr 1 / 2 Ti 1 / 2 )O 3 (PZT) was investigated to determine the influence of different solid state processing conditions on dielectric and ferroelectric properties. The ceramic materials were characterized using x-ray diffraction, dielectric measurements, and hysteresis measurements. To stabilize the perovskite phase, the columbite route was utilized with a double crucible technique and excess PbO. The phase-pure perovskite phase of PNN-PZN-PZT ceramics was obtained over a wide compositional range. It was observed that for the ternary system 0.5PNN-(0.5- x)PZN-xPZT, the change in the transition temperature (T m ) is approximately linear with respect to the PZT content in the range x = 0 to 0.5. With an increase in x, T m shifts up to high temperatures. Examination of the remanent polarization (P r ) revealed a significant increase with increasing x. In addition, the relative permittivity (∈ r ) increased as a function of x. The highest permittivities (∈ r = 22,000) and the highest remanent polarization (P r = 25 μC/cm 2 ) were recorded for the binary composition 0.5Pb(Ni 1 / 3 Nb 2 / 3 )O 3 -0.5Pb(Zr 1 / 2 Ti 1 / 2 )O 3 .

Synthesis, formation and characterization of zirconium titanate (ZT) powders

Zirconium titanate (ZrTiO4) powders have been prepared and characterised by differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) techniques. The effect of calcination temperature, dwell time and heating/cooling rates on phase formation, morphology and particle size distribution of the powders are examined. The calcination temperature and dwell time have been found to have a pronounced effect on the phase formation and particle size of the calcined zirconium titanate (ZT) powders. It has been found that the minor phases of ZrO2 and TiO2 tend to form together with ZrTiO4, depending on calcination conditions. Optimisation of calcination conditions can lead to a single-phase ZrTiO4 in an orthorhombic phase. D 2002 Elsevier Science B.V. All rights reserved.

The study of dielectric diffuseness in the Ba(Mg1/3Nb2/3)O3?BaTiO3 ceramic system

The dielectric properties of Ba(Mg1/3Nb2/3)O3 (BMN)-substituted BaTiO3 (BT) (xBMN–(100−x)BT) ceramics, where x = 0–5 mol%, were prepared by a high-temperature solid-state reaction technique. It was found that the substitution of Mg2+ and Nb5+ at the Ti-site of the BMN–BT ceramics caused compositional inhomogeneity, leading to a diffuse phase transition (DPT). Discontinuous grain growth accompanied with excellent dielectric diffuseness was found in 3–5 mol% BMN specimens. The maximum solubility limit of Mg/Nb substitution was assumed to be between 3 2 mol%, the maximum dielectric constant decreased and the Curie temperature shifted downwards on the lower temperature side.

Fabrication of transparent lead-free KNN glass ceramics by incorporation method

The incorporation method was employed to produce potassium sodium niobate [KNN] (K0.5Na0.5NbO3) glass ceramics from the KNN-SiO2 system. This incorporation method combines a simple mixed-oxide technique for producing KNN powder and a conventional melt-quenching technique to form the resulting glass. KNN was calcined at 800° C and subsequently mixed with SiO2 in the KNN:SiO2 ratio of 75:25 (mol%). The successfully produced optically transparent glass was then subjected to a heat treatment schedule at temperatures ranging from 525° C -575° C for crystallization. All glass ceramics of more than 40% transmittance crystallized into KNN nanocrystals that were rectangular in shape and dispersed well throughout the glass matrix. The crystal size and crystallinity were found to increase with increasing heat treatment temperature, which in turn plays an important role in controlling the properties of the glass ceramics, including physical, optical, and dielectric properties. The transparency of the glass samples decreased with increasing crystal size. The maximum room temperature dielectric constant (εr) was as high as 474 at 10 kHz with an acceptable low loss (tanδ) around 0.02 at 10 kHz.

Characterization and properties of Sb-doped BaTiO3 powders

Improved single-phase nanocrystalline BaTiO3 powders may be prepared at 700°C by the sol-gel acetate process to which 1–3wt% Sb is added as dopant. Following calcination at 1200°C, the resulting average particle size as determined by scanning electron microscopy analysis is in the range of 50–150nm. The dielectric results show that fired samples containing 1wt% Sb have the highest relative permittivity, with er≈4500 and TC=52°C, whereas undoped samples have er≈3300 and TC=120°C.

Effects of NiO nanoparticles on the magnetic properties and diffuse phase transition of BZT/NiO composites

A new composite system, Ba(Zr0.07Ti0.93)O3 (BZT93) ceramic/NiO nanoparticles, was fabricated to investigate the effect of NiO nanoparticles on the properties of these composites. M-H hysteresis loops showed an improvement in the magnetic behavior for higher NiO content samples plus modified ferroelectric properties. However, the 1 vol.% samples showed the optimum ferroelectric and ferromagnetic properties. Examination of the dielectric spectra showed that the NiO additive promoted a diffuse phase transition, and the two phase transition temperatures, as observed for BZT93, merged into a single phase transition temperature for the composite samples.

Morphotropic Phase Boundary of Lead-Free Piezoelectric Ceramics from BNT- KN System

In this research work, the investigation of the morphotropic phase boundary, physical properties and electrical properties of lead- free piezoelectric materials of bismuth sodium titanium oxide: (Bi0.5Na0.5)TiO3 (BNT) and potassium niobium oxide : KNbO3 (KN) in the ceramic system of (1-x)BNT- xKN where x= 0.00, 0.03, 0.05, 0.08, 0.10 and 0.15 by modified mixed oxide method was carried out. The BNT and KN powders were prepared separately using calcination technique with optimum calcination temperature for producing both BNT and KN powders of about 800°C. XRD results revealed that the BNT-KN ceramics with low KN content of x less than 0.05 contain ferroelectric perovskite phase with rhombohedral symmetries while the higher KN content ceramics have mixed symmetries between rhombohedral and orthorhombic. From the evidences including phases, microstructures and dielectric data of the BNT-KN ceramics, it may be assumed that the morphotropic phase boundary may be at around the composition of x = 0.05.

Antibacterial Compounds from Propolis of Tetragonula laeviceps and Tetrigona melanoleuca (Hymenoptera: Apidae) from Thailand

This study investigated the chemical composition and antimicrobial activity of propolis collected from two stingless bee species Tetragonula laeviceps and Tetrigona melanoleuca (Hymenoptera: Apidae). Six xanthones, one triterpene and one lignane were isolated from Tetragonula laeviceps propolis. Triterpenes were the main constituents in T. melanoleuca propolis. The ethanol extract and isolated compounds from T. laeviceps propolis showed a higher antibacterial activity than those of T. melanoleuca propolis as the constituent α-mangostin exhibited the strongest activity. Xanthones were found in propolis for the first time; Garcinia mangostana (Mangosteen) was the most probable plant source. In addition, this is the first report on the chemical composition and bioactivity of propolis from T. melanoleuca.

Dielectric properties of lead-free solid solution of Bi0.487Na0.487La0.017TiO3 and BaTiO3

Bismuth sodium titanate (Bi0.5Na0.5TiO3; BNT) is one of the most preferred materials for the preparation of lead-free ceramics; however its dielectric property is lower than that of lead-based materials. Thus, the substitution of A and B-site cations is considered to be one of the best solutions in order to improve both the dielectric and piezoelectric properties. In this study, lead-free ceramics from bismuth sodium lanthanum titanate (Bi0.487Na0.487La0.017TiO3; BNLT) and barium titanate (BaTiO3; BT) systems were prepared by a modified two-step mixed oxide method. BT powder was added to BNLT powder with the desired compositions of (1 − x)BNLT–xBT, where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10. It was found that the addition of BT in the BNLT improved the electrical properties of ceramics. Phase transition of rhombohedral to tetragonal structure was significantly dependent on the amount of BT added. It was also found that the change in crystal structure affected the ferroelectric property of the ceramics where the transition from ferroelectric to antiferroelectric started from the samples with x ≥ 0.06 mol% and higher. This may be useful in terms of using these materials in the desired applications.

Influence of B2O3 on electrical properties and phase transition of lead-free Ba(Ti0.9Sn0.1)O3 ceramics

The phase transition and electrical properties of Ba(Ti0.9Sn0.1)O3 ceramics with B2O3 added were investigated to explore the effect of B2O3 addition on enhanced densification and dielectric constant of these ceramics. With increasing B2O3 content, a linear reduction of ferroelectric to paraelectric transition temperature was observed. In addition, higher B2O3 concentrations enhanced a ferroelectric relaxor behavior in the ceramics. Changes in this behavior were related to densification, second-phase formation and compositional variation of the ceramics.