Rungnapa Tipakontitikul

Effects of MnO2 Addition on the Dielectric Behaviors of the PZT-PMN Ceramics

The PZT-PMN ceramics system proposed for piezoelectric transformation application was derived from Pb(Zr 0.52 Ti 0.48 )O 3 and Pb(Mg 0.66 Nb 0.33 )O 3 based compositions that obtained from the culombite method. The effect of MnO 2 addition on microstructure, physical properties and piezoelectric properties were investigated. The XRD results show that no phase transformation observed for all sintered PZT-PMN samples doped with MnO 2 . Presence of MnO 2 also improved their sinterability of the ceramics as evidenced by SEM micrographs. Though, MnO 2 addition tends to lower the dielectric constant in this ceramics but it improved Q m from 115 to a maximum value of 1669 in the ceramic with 8 mol% of MnO 2 . Also, increasing of d 33 from 28.53 to 114.19 pC/N was found for MnO 2 in range 0 to 4 mol%. However, the k p values are clearly increased with increasing of MnO 2 content.

Formation of Nano-Sodium Niobate Crystals in Ferroelectric Glasses and Glass-Ceramics of the Na2O-Nb2O5-Al2O3-SiO2 System

Ferroelectric glasses and glass-ceramics were prepared from selected composition in the Na 2 O-Nb 2 O 5 -Al 2 O 3 -SiO 2 glass system. Small amount of TiO 2 was also added. Conventional melt-quenching technique was employed for a glass production and the selected bulk parent glass samples were subjected to the heat-treatment process. Clear transparent glass was obtained but with surprise presence of precipitated nano-size NaNO 3 crystals as the result of phase separation. For the heat-treated samples, the longer treatment time induced a higher volume fraction of the NaNbO 3 crystals, but thier size was not significantly increased. Dielectric response of the glass-ceramics contained NaNbO 3 crystals is the combination of all contribution from both crystalline phases and the glass matrix.

Crystallization and Dielectric Properties of Ferroelectric Glass-Ceramics Containing Sodium Niobate Crystals

Ferroelectric glass-ceramics of the sodium-niobate-aluminum-silicate (NaO-Nb2O5-SiO2+Al2O3) system, with various amounts of ZrO2 added, were synthesized through melt casting followed by controlled crystallization. The crystallization behavior, microstructure, and dielectric performances of the glass-ceramics were investigated. The addition of 1 mol% ZrO2 to the glass-ceramics improved the glass forming ability of the phase separated melts and supported the formation of transparent glass-ceramics after precipitation of the NaNbO3 ferroelectric crystals. The presence of ZrO2 also promoted a well-defined microstructure which presented as an improvement in the dielectric constant of the glass-ceramic heat treated at 750°C for 1 h. Dipole polarization was responsible for the dielectric response of the glass-ceramics, but due to structural heterogeneities coupled with high migration of the mobile species, a complicated dielectric relaxation mechanism was also found.

Formation and Dielectric Properties of NaNbO3 Phase in the Ferroelectric Glass-Ceramic Na2O-Nb2O5-Al2O3-SiO2 System with Addition of ZrO2

Ferroelectric glass-ceramics of the Na2O-Nb2O5-Al2O3-SiO2 system were prepared via conventional melt quenching followed by heat treatment at 790°C for various times. The ZrO2 content was also added to the glass compositions as to investigate its effect on crystalline phase formation and relevant properties. The results show that NaNbO3 and NaNbO8 are the main phases embedded in the glass matrix. Increasing treatment time, both NaNbO3 and NaNbO8 are developed to higher concentration. Crystallite sizes of the NaNbO3 crystals were not increased with treatment time. The dielectric properties of the glass–ceramics have a strong dependence on the phase compositions. The dielectric–temperature characteristics of the samples show stability up to 200°C. At higher temperature, the evidences of transition of the NaNbO3 phases are clearly seen. The major phase transition is at temperature above 400°C. The dielectric constants measured at 400°C with frequency of 1 kHz are in order of 104.

Dielectric Properties of Ferroelectric Glass-Ceramics of the Na2O-K2O-Nb2O5-Al2O3-SiO2 System with Partial Substitution of K2O for Na2O

Substitution of K2O for Na2O content was performed in ferroelectric glass-ceramics of the Na2O-Nb2O5-Al2O3-SiO2 system and its effect on crystallization process and the associated properties were investigated. Conventional melt quenching method was employed for parent glass production. Phase identification shows that NaNbO3 perovskite phase is crystallized spontaneously during quenching along with other two phases, NaNbO8 and phase of the sodium alumino silicate compound. No evidence of complex phases occurring due to presence of K2O. However, the results of dielectric measurements revealed complex phase transition from room temperature up to 400°C. First order transition can be observed in range 150°C–250°C. While the main transition seen in dielectric-temperature plot is at 380°C with dielectric constant of 1370 (at 1 kHz). This is associated to transition of NaNbO3 from orthorhombic to perovskite cell with cubic symmetry. Higher dielectric loss is observed at higher temperature. It is also noted that entering of K2O content reduce dielectric constant of the glass-ceramics system.

Crystallization Behavior of Ferroelectric Glass-Ceramics of the Na2O-Nb2O5-Al2O3-SiO2 System Contained TiO2

The ferroelectric glass-ceramic of the composition Na2O-Nb2O5-Al2O3-SiO2 was prepared by controlling crystallization of the glass that added with small amount of TiO2. The effect of TiO2 content on crystallization behavior and the dielectric property were determined. X-ray diffraction studied indicated that NaNbO3, NaNbO8 and a compound of alkali alumino silicate composition were readily formed in the as-quenched glass as the product of phase separation. After treatment at 700oC for various times, NaNbO3 volume fraction was found to increase with time. Crystalline size of the NaNbO3 was lower than 300 nm and it was developed with treatment time. Presence of TiO2 had considerably effect on NaNbO3 volume fraction when treatment time shorter than 1.0 h. The dielectric response of the glass-ceramic samples was found to arise from all contributions of crystalline phases and glass matrix responds.

Formation of NaNbO3 Crystals in Dielectric Glass and Glass-Ceramics of a Na2O-Nb2O5-Al2O3-SiO2 System

Dielectric glass and glass-ceramics were derived from Na2O-Nb2O5-Al2O3-SiO2 system. Small amount of TiO2 were also introduced into glass compositions to study crystallization behavior of the glass with present of this nucleating agent. Conventional melt-quenching technique was employed for a glass production and the selected bulk glass samples were subjected to the heat-treatment process at appropriate temperature. After six different glass compositions were produced, and by observation with necked eyes, all obtained glass samples are in light brown color and some samples were opaque due to crystallization took place during quenching. Phase identification through XRD patterns show that there were 3 phases, NaNbO3, NaNbO8 and a sodium aluminum silicate compound, found in those opaque glass samples. NaNbO3 is a predominant phase in all samples. Fortunately, clear transparent glass was obtained from the composition with no TiO2 addition. Heat treatment of this glass did not induce phase change, three aforementioned phases still present. Increasing heat treatment time promoted a higher of observed intensity of NaNbO3. But the NaNbO3 crystalline size was not significantly developed with time. The dielectric response of the NaNbO3 crystals in the glass-ceramics samples are influenced by presence of other crystalline phases.

Crystallization Behavior and Dielectric Properties of Ferroelectric Glass-ceramics Containing BNN and NN Crystals

Glass samples with compositions of 16Na2O-8BaO-26Nb2O5-50SiO2 (mol%) were prepared using the melt-quenching method and then heat-treated under different temperatures and times. The resulting crystallization behavior was then studied through X-ray diffraction and scanning electron microscopy, and the dielectric properties were measured using an impedance analyzer in the frequency range 10 Hz–10 MHz. The experimental results showed that all of the obtained glass-ceramic samples heat treated using different temperatures and times contained mixed-crystalline phases between Ba2NaNb5O15 (BNN) with tungsten-bronze structure and NaNbO3 (NN) with a perovskite structure. The crystals of these two phases were distributed randomly throughout the bulk glass-ceramics at the nano-scale. The plots of the dielectric constant versus the measurement temperature reveal a serial phase transition with a complex mechanism of the dielectric relaxation. The serial phase transition is related to the dielectric response of both the BNN and the NaNbO3 crystals. Also, the presence of the BNN phase tended to lower the Curies temperature. The dielectric spectroscopic investigations revealed that a dipolar polarization mechanism is responsible for the dielectric contribution of the bulk glass-ceramics. The presence of the BNN phase gave the ferroelectric glass-ceramics higher dielectric constants. The dielectric properties of the glass-ceramics were found to be highly sensitive to changes in treatment conditions. An increase in treatment temperature gave rise to glass-ceramics with larger crystallites and higher dielectric permittivity but an increase in treatment time also allowed the glass matrix to be annealed with the effect being a lower dielectric permittivity and lower phase transition levels.

The Effect of Nd3+Addition on Crystallization Behavior and Related Properties of the Ferroelectric Glass-Ceramics Na2O-BaO-Nb2O5-SiO2 Based Composition

Ferroelectric glass-ceramics of the Na2O-BaO-Nb2O5-SiO2 system were prepared from parent glass of composition 20Na2O-4BaO-26Nb2O5-50SiO2. Nd2O3 was systematically added in the range 0–3 mol% to the glass compositions as to study its effect on crystallization behavior of the glass and the dielectric properties of the associated glass-ceramics. Heat treatments of the as-quenched samples were performed at the selected temperatures referring to thermal properties that described by the differential thermal analysis. X-ray diffraction studies indicated that NaNbO3 and NaBa2Nb5O15 crystals formed as two main crystalline phases. Involvement of Nd3+ ions in the glass network suppressed precipitation of the NaBa2Nb5O15 phase. The dielectric constant measured at room temperature for glass-ceramic samples were found to sensitive to presence of NaBa2Nb5O15 phase. The present work showed that introduction of Nd3+ into the Na2O-BaO-Nb2O5-SiO2 glass-ceramics system induce slightly change of the dielectric properties.

Enhanced sinterability and electrical properties of Bi2O3-added Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics

ABSTRACT The ceramics of Bi2O3-added Ba0.85Ca0.15Zr0.1Ti0.9O3 or BCZT-xBi (where x = 0.005, 0.01, 0.02 and 0.1 mol fraction) were fabricated from sol-gel auto-combustion derived BCZT and commercial Bi2O3 powders. In this study, BCZT-0.02Bi ceramic sintered at 1200°C for 2 h was found to be the optimum composition with high relative density and homogeneous microstructure. The temperature at maximum dielectric constant (Tmax) of this sample was near room temperature, rendering a high dielectric constant value (∼1653). Frequency dependence of Tmax suggested the relaxor behavior which was also supported by slim ferroelectric hysteresis loops. Since a relatively large breakdown voltage (> 70 kV/cm) was observed, the BCZT-0.02Bi ceramic could be a potential lead-free electrostrictive/piezoelectric material for actuator applications.