Piyachon Ketsuwan

Structure and electrical properties of double perovskite Sr(Ni1/2Mo1/2)O3 ceramics

The double perovskite Sr(Ni1∕2Mo1∕2)O3 has been prepared with solid-state reaction and was characterized by x-ray diffraction technique. It has been indicated that the single phase is formed at 1300°C in air. The compound undergoes a phase transition at 280°C, where the structure of the ordered perovskite type changes from tetragonal (I4∕m) to cubic (Fm3¯m). Dielectric constant (er) and dielectric loss (tanδ) are observed at the transition point. The conductivity of the sample has been studied, and the slope of dc conductivity versus the inverse of temperature corresponds to an Arrhenius activation energy in the range of 0.34–0.46eV. This range of activation is nearly double ionized oxygen vacancies VO⋅⋅ in the resistivity transition of other perovskite oxides.

Microstructure and Electrical Properties of Niobium Doped Barium Titanate Ceramics

The effects of Nb addition on phase, microstructure and electrical properties of barium titanate ceramics were investigated. Nb-doped barium titanate ceramics (BaTi1-xNbx)O3, x = 0 to 0.02) were prepared by conventional mixed-oxide method. All barium titanate compositions show tetragonal perovskite structure. Low Nb concentration (x = 0.005) results in abnormal grain growth in barium titanate. However, the grain size becomes uniform and decreases as Nb content increases, suggesting Nb inhibits grain growth in the studied composition range. The dielectric constant increases as the amount of Nb increases. The temperature of tetragonal to cubic phase transition shifts to lower temperature and the temperature curves become broadening with increasing of Nb content. Measurement of ferroelectric P-E hysteresis loop at 50 Hz and applied electric field of 15 kV shows that the remanent polarization of barium titanate ceramics tends to decrease as Nb content increases. Change in dielectric properties and the P-E hysteresis loop did not show large aging effect in the Nb-doped barium titanate ceramics.

Effects of Iron Addition on Electrical Properties and Aging Behavior of Barium Titanate Ceramics

In this study, the influences of Fe addition on phase formation and electrical properties of Ba(Ti 1 − x Fe x )O 3 with x = 0 to 0.02 were investigated. In addition, aging behavior of the ceramics was also investigated. The XRD analysis showed that the crystal structure of Ba(Ti 1 − x Fe x )O 3 changed from tetragonal to hexagonal as Fe concentration increased to x = 0.015, causing a noticeable decrease in the dielectric properties. From ferroelectric hysteresis (P-E) loops measurements, with increasing Fe content the saturation polarization decreased, while the coercive electric field increased at low concentration (x ≤ 0.01) with tetragonal structure. At x ≥ 0.015, with paraelectric hexagonal phase, no P-E hysteresis loop was observed at room temperature. Room temperature aging study showed that the ferroelectric P-E hysteresis loops became constricted loops during aging in Ba(Ti1 − x Fe x )O 3 with ferroelectric tetragonal phase. The dielectric constant also decreased during aging.

Effects of vibro-milling time on phase formation and particle size of Zn3Nb2O8 nanopowders

Zinc niobate, ZnNb2O6, nanopowders was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of ZnNb2O6 powder was investigated. The formation of the ZnNb2O6 phase investigated as a function of calcination conditions by DTA and XRD. The particle size distribution of the calcined powders was determined by laser diffraction technique, while morphology, crystal structure and phase composition were determined via a SEM techniques. In addition, by employing an appropriate choice of milling time, a narrow particle size distribution curve was also observed.

Effects of Manganese Addition on Phase Formation, Microstructure and Electrical Properties of Barium Titanate Ceramics

In this study, the influence of Mn addition on phase formation, microstructure and electrical properties of Ba(Ti1-xMnx)O3 where x = 0.01 to 0.2 was investigated. The XRD patterns showed that the crystal structure of Ba(Ti1-xMnx)O3 at room temperature changed from tetragonal to hexagonal as Mn concentration increased, which also caused the room temperature dielectric constant decrease from 1143 to 47. The microstructure of Ba(Ti1-xMnx)O3 ceramics at low concentration revealed a bimodal microstructure. As the x value increased, the well grown grains decreased with the extent of fine-grained increased. Ferroelectric hysteresis (P-E) loop was not clearly observed as Mn concentration increased because of the formation of paraelectric hexagonal phase

Dielectric Aging of Cr-Doped PZT Ceramics

The aging of dielectric properties of Cr-Doped Pb(Zr0.52Ti0.48)O3 were investigated. The composition of Pb(Zr0.52Ti0.48)O3 with 0.1, 0.2, 0.4, 0.6, 1.0 and 3.0 mol% of Cr2O3 addition were prepared by conventional mixed oxide technique. The aging has been measured at room temperature after quenching from high temperatures above the Curie temperature. The dielectric aging of all compositions revealed relaxor aging behavior. The aging rate of stable stage obeyed a logarithmic time dependence, while the aging rate decreased with increasing Cr2O3 at low concentration (0.1–0.6). Further increase in Cr2O3 concentration, the aging rate turned to increase.

Dielectric and Ferroelectric Properties of (Cr,Nb)-Doped Lead Zirconate Titanate Ceramics

The 3 mol% Nb2O5 doped Pb(Zr0.52Ti0.48)O3 with addition of 1-3 mol% Cr2O3 prepared via the solid-state reaction technique have been investigated. The XRD shows that a sample is primarily in both tetragonal and rhombohedral phases coexist and the amount of rhombohedral phase decreases that is due to the donor (Nb) dopant reduces the number of oxygen vacancies and leads to a lower amount of rhombohedral phase. The maximum dielectric constant tend to decrease with increasing Cr doping concentration from 0.1 to 1 mol%. Further increase in Cr concentration, the maximum dielectric constant increase dramatically. The hysteresis loop measurements, the electrical coercivity and the remnant polarization do not show a systematic trend at low concentration of Cr doping. It is possibly due to the partial solubility of Cr doping. The observations clearly indicate the hardening behavior at higher concentration because of more solubility of Cr.

Aging Behavior of (Cr,Nb)-Doped PZT Ceramics

The aging behavior of 3 mol% Nb2O5Pb(Zr0.52Ti0.48)O3with addition of 0.1–3 mol% Cr2O3prepared via the solid-state reaction technique have been investigated. The aging rate increased with increasing Cr concentration from 0.1 to 0.6 mol%. Further increase in Cr concentration, the aging rate decreased dramatically. From ferroelectric hysteresis loops measurements, the decrease of polarization existed in all of concentrations.

Investigations on Morphology and Ferroelectric Properties of NaNbO3–PbTiO3 Composite Ceramics

Ceramics in NN–PT system with a formula (1−x)NaNbO3–(x)PbTiO3 (where x = 0, 0.1, 0.2, …, 1.0) were prepared by a solid state mixed oxide technique. The phase formation behavior and microstructure were studied using x-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The dielectric and ferroelectric properties of the compounds were studied and discussed. Phase pure perovskites of NN–PT ceramics were obtained over a wide compositional range. This work was then aimed to determine the phase formation, morphology, dielectric and ferroelectric properties of NN–PT ceramics. Interestingly, the results showed that the addition of PT have been strongly affected on morphology and ferroelectric properties of NN ceramics.

Dielectric Properties of Bi0.2K0.8(Zn0.1Ti0.1)Ta0.8O3 Ceramics

The Bi0.2K0.8(Zn0.1Ti0.1)Ta0.8O3 and Li doped ceramics prepared via the solid-state reaction technique were investigated. The XRD patterns show the single phase cubic perovskite structure without any evidence of secondary phases when sintered at 1250 oC for undoped Bi0.2K0.8(Zn0.1Ti0.1)Ta0.8O3 and sintered at 1100 oC for Li doped one. The dielectric properties indicate the diffused phase transition (DPT). The dielectric loss of undoped ceramic increases with increasing frequency in temperature range 270 oC down to -150 oC, which suggests low temperature relaxation, while the dielectric loss of Li doped ceramic reveals the interesting lower value over a wide temperature range of about 0 - 300 oC.