G. Rujijanagul

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.

Antiferroelectric-ferroelectric phase transitions in Pb1−xBaxZrO3 ceramics: Effect of PbO content

The irreversibility of the antiferroelectric (AFE) to FE phase transition in Pb1−xBaxZrO3, x=0.75–0.1, compositions is shown to be a consequence of lattice vacancies arising from PbO evaporation during ceramic processing. Previously, the absence of a FE→AFE cooling transition was thought to be due to the transformational strain and the fragmentation of ferroelectric domains. Appropriate compensating levels of excess PbO added to starting powders generate the FE→AFE transition. For lower levels of Ba2+ substitution, x=0.05, the transition is reversible in noncompensated samples, but PbO compensation raises the FE→AFE transition temperature by ∼25°C.

Microstructure and electrical properties of BaFe 0.5Nb 0.5O 3 Doped with GeO 2 (1-5 wt.%)

In this work, the effects of GeO2 dopant on the electrical properties of BaFe0.5Nb0.5O3 (BFN) perovskite ceramics were investigated. The BFN powder was prepared by a conventional mixed-oxide method using stoichiometric amounts of BaCO3, Fe2O3 and Nb2O5. Afterward the GeO2 contents, ranging from 1 to 5 wt.%, were added to the calcined BFN powder and mixed via vibro-milling method. The mixtures were pressed and sintered at 1125–1150°C for 4 h to form dense ceramics. We showed that the addition of GeO2 caused a reduction of grain size and formation of secondary phases: Ba3Fe2Ge4O14 and BaGeO3. The maximum densities of these BFN doped with GeO2 ceramics were slightly lower than those of the pure BFN due to the occurrence of pores. We also found that the GeO2 doping could improve the dielectric properties of these ceramics at room temperature (25°C). The 1 wt.% GeO2 doped sample exhibited higher dielectric constant of about 1800 and lower dielectric loss of 0.45 comparing to that of pure BFN. However, the dielectric constant values of these ceramics at high temperature (>25°C) were decreased significantly with the increase of GeO2 concentration. In addition, the GeO2 additive gave a weak ferroelectric behavior, leading to change in the pyroelectric coefficient and spontaneous polarization of the GeO2 doped BFN ceramics.

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.

Structures and Properties of Lead-Free NKN Piezoelectric Ceramics

In this work, the preparation of sodium potassium niobate (Na0.5K0.5)NbO3 (NKN) ceramics were carried out by the conventional method. The effect of calcination temperatures, dwell time and heating rate on phase formation was investigated. Earlier work reported that to achieve the density of NKN ceramic over 95% of its theoretical density is rather difficult. In this work, firing conditions and heating and cooling rates were carefully varied to fabricate the NKN ceramics. X-ray diffraction (XRD) techniques were used to investigate the phase evolution of the calcined powders and sintered bodies. Microstructures of sintered pellets were studied by the scanning electron microscopic (SEM) techniques. Dielectric and ferroelectric properties were also investigated and reported.

Effect of Heat Treatment Conditions on Properties of Lead‐Free Bi2GeO5 Ferroelectric Glass Ceramics

Nowadays, lead‐free ferroelectric materials have attracted much interest among materials scientists as a result of environmental concern. The bismuth germanate (Bi2GeO5) phase, one of the lead‐free ferroelectric crystals, is of particular interest as its composition already contains good glass former (GeO2) and can be prepared by an alternative glass ceramic route. In this work, the conventional melt‐quenching method was used to produce the parent glass with composition of 60 mol% BiO1.5:20 mol% GeO2:20 mol% BO1.5. The as‐received glass pieces were subjected to the heat treatment schedule at various crystallization temperatures and dwell‐times. The glass and glass ceramics samples were then investigated by XRD, Raman spectroscopy and their dielectric properties were also measured. The XRD and Raman spectroscopy showed that the crystallinity of the prepared glass ceramics depended very much on crystallization temperature and dwell‐time. The larger dielectric constant and lower dielectric loss were obtained...

Ferroelectric and Pyroelectric Properties of 0.8PbZr0.52Ti0.48O3–0.2BaFe0.5Nb0.5O3 Ceramics

The solid solution 0.8PbZr 0.52 Ti 0.48 O 3 –0.2BaFe 0.5 Nb 0.5 O 3 (P8B2) ceramic was prepared by the mixed oxide method. The aim of this work is to focus on the ferroelectric and pyroelectric properties of the ceramic. The phase formation behavior was studied using X-ray diffraction (XRD) methods. The ferroelectric properties were measured by a Sawyer-Tower circuit. Particularly, we measured the dielectric and pyroelectric properties by an automatic corrected data with Hewlett-Packard LCZ meter in the environmental chamber. The optimum conditions for fabrication of 0.8PZT–0.2BFN ceramics were found at 1100°C for calcination and 1200°C for sintering temperature. From the hysteresis loop measurement, the remanent polarization (P r ) and coercive field were 21 μC/cm 2 and 6.4 kV/cm, respectively. The phase transition temperatures (T c ) obtained by pyroelectric measurements are in good agreement with the values obtained from the dielectric study.

High Dielectric and Piezoelectric Properties Observed in Annealed Pb0.88Sr0.12Zr0.54Ti0.44Sb0.02O3 Ceramics

The dielectric, ferroelectric, and piezoelectric properties of ceramics from the Pb0.88Sr0.12 Zr0.54Ti0.44Sb0.02O3 system were investigated as a function of annealing time after being prepared via the solid-state method. Following the annealing process, a shift in the ferroelectric to paraelectric transition temperature (Tm) was observed. In addition, a high relative permittivity >24300 at Tm was recorded for the 64 h annealed sample which was 52% higher than that of the as-sintered samples. The increased annealing time produced an enhancement in the ferroelectric properties and a high piezoelectric coefficient (d33) of 670 pC/N was also observed for the 64 h annealed sample.

Effects of vibro-milling on relaxor ferroelectric behavior and phase transition of lead-free Ba(Zr0.25Ti0.75)O3 ceramics

Lead-free Ba(Zr0.25Ti0.75)O3 ceramics were synthesized from powders prepared by a conventional mixed oxide and vibro-milling method to investigate the phase transition, dielectric response, and ferroelectric properties of the prepared samples. Compared to a conventional sample, the samples prepared by the vibro-milling method showed a higher dielectric constant at the ferroelectric-to-paraelectric transition temperature. The vibro-milling method also produced a stronger frequency dependence on the dielectric constant. To confirm the dielectric properties and phase transition behavior, ferroelectric hysteresis measurements were carried out in the temperature range −40°C to 80°C. The microstructural properties of the samples were investigated and the results were then correlated with the characteristics of the milled and calcined powder as well as the grains of the ceramics.

Phase transition behavior in (1 − x)PZT–xBiAlO3 ceramics

In this study, a new ceramic with the composition (1 − x)Pb(Zr0.52Ti0.48)O3–xBiAlO3 was fabricated using the solid state method. Phase transition characteristic and dielectric response were investigated. With increase in the content of BiAlO3, a transformation from the tetragonal to the rhombohedral phase was observed. The addition also enhanced the degree of phase transition diffuseness and produced a decrease in the ferroelectric-to-paraelectric phase transition temperature. The results suggested that BiAlO3 has a strong effect on the transition behavior of the solid solution. It is proposed that lattice distortion and compositional fluctuation are responsible for these effects.