Rattiphorn Sumang

The Effect of Calcination Temperatures on the Phase Formation and Microstructure of (Pb1-xSrx)TiO3 Powders

(Pb1-xSrx)TiO3 (PST) (x=0.25, 0.50) powders were synthesized by a mixed oxide solid-state reaction method under various calcination temperatures (600-1100oC). Powder samples were characterized using thermogravimetric (TGA), differential thermal analysis (DTA), x–ray diffractrometer (XRD) and scanning electron microscopy (SEM). The results showed that a single-phase of PST for x=0.25 and 0.50 powders was successfully obtained with a calcination condition of 950 oC for 2 h with a heating/cooling rate of 5oC/min. The TGA-DTA results corresponded to the XRD investigation. The lattice parameter a increased whilst the lattice parameter c decreased with increasing calcination temperatures. The tetragonality of powders decreased with an increase of calcination temperatures. The average particle size of the powders increased with the increase of calcination temperature.

Phase Formation, Microstructure and Phase Transition of Lead Barium Titanate Ceramics: Effect of PbO Content

Monophasic oxides of the formula, (Pb 0.975 Ba 0.025 )TiO 3 with excess PbO (0, 1, 3, 5 and 10 wt%) were prepared by a mixed oxide method. It was found that lead barium titanate powders indexed in a tetragonal structure. The impurity phases were detected in the calcined powders with ≥ 3 wt% of excess PbO. The impurity phases were not present in any ceramic samples. The c/a ratio was decreased with increasing of excess PbO. The average particle size and the average grain size of the PBT increased with increasing of PbO contents. The density can be improved by adding 1 wt% of excess PbO. The DSC results indicated that the Curie point shifted to higher temperature when the excess PbO was higher than 3 wt%.

EFFECT OF SINTERING TEMPERATURE ON THE CRYSTAL STRUCTURE, MICROSTRUCTURE AND PHASE TRANSITION OF (Pb1-xSrx)TiO3 CERAMICS

Polycrystalline (Pb1-xSrx)TiO3 (PST) (x = 0.25, 0.50) ceramics were synthesized by the solid-state reaction method. PST sintering temperatures ranged between 1050–1250°C. The samples were characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The sintered pellets showed pure perovskite in all samples. The lattice parameter c increased, while the lattice parameter a decreased with increasing sintering temperatures. The tetragonality and average grain sizes increased when sintering temperatures were increased. The dielectric constants vs temperature curves of PST ceramics with x = 0.25 and x = 0.50 associated with the ferroelectric to paraelectric phase transition, showed a maximum peak at around 311 and 139°C, respectively. The dielectric constants of both compositions were related with their densities.

The Effect of Excess PbO on Crystal Structure, Microstructure, Phase Transition and Dielectric Properties of (Pb0.75 Sr0.25)TiO3 Ceramics

This study investigated the effect of excess PbO on the crystal structure, microstructure, phase transition and dielectric properties of (Pb0.75Sr0.25)TiO3 (PST25) ceramics. The PST25 ceramics were synthesized by the solid-state reaction method with various excess PbO levels (0, 1, 3, 5 and 10 wt.%). The excess PbO was added to compensate for the lead loss from evaporation during calcination and sintering at 950°C and 1150°C. The X-ray characterization revealed that all samples had a tetragonal structure and impurity phases since PbO and PbO2 were detected in the calcined powders with higher than 3 wt% of excess PbO. A pure perovskite phase was obtained in all ceramic samples. The c/a ratios tended to decrease with an increasing excess PbO in the calcined powders and sintered pellets. The average particle size and the average grain size of the PST tended to increase with an increase of PbO content. With 1 wt.% of excess PbO, the highest density and a broader dielectric peak were obtained. The dielectric spectrum was not present in the 3, 5 and 10 wt.% excess of PbO samples. The DSC results indicated that the Curie point shifted to a higher temperature with the increase in the excess of PbO until 3 wt.%, then slightly decreased with higher excess PbO.

The Influence of Firing Temperatures on the Crystal Structure, Microstructure and Dielectric Properties of 0.79Bi0.5Na0.5TiO3-0.18Bi0.5K0.5TiO3-0.03BiFeO3 Ceramics Prepared via the Combustion Technique

Polycrystalline samples of 0.79Bi0.5Na0.5TiO3−0.18Bi0.5K0.5TiO3−0.03BiFeO3 (abbreviated as BNKFT) lead-free piezoelectric ceramics were synthesized by the combustion technique. BNKFT was calcined from 600°C to 800°C for 2 h. and the sintering temperature ranged from 900°C to 1075°C for 2 h. The XRD analysis exhibited that the BNKFT powders belonged to a rhombohedral structure. A second phase of K4Ti3O8 was detected in the powders calcined below 750°C. The sintered pellets showed a pure perovskite phase in all samples. The microstructure of BNKFT powders exhibited an almost-spherical morphology and had a porous agglomerated form. The average particle size and the average grain size of BNKFT powders and ceramics increased with the increase of firing temperatures. The highest densities (ρ = 5.85 g cm−3), maximum dielectric constant (ϵr = 8,530), lowest dielectric loss (tanδ = 0.02) maximum remnant polarization measured at 40 kV/cm (P r = 20.1 μC/cm2) and the maximum piezoelectric coefficient (d 33 = 213 pC/N) were obtained from the sample sintered at 1050°C. With a lower firing temperature, the properties of the BNKFT ceramics prepared by the combustion technique were better than those prepared by the solid-state reaction method.

The Effect of Excess PbO on Crystal Structure and Microstructure of (Pb0.925Ba0.075)TiO3 Ceramics

In this work, we studied the effect of excess PbO doping on lead barium titanate [(Pb0.925Ba0.075)TiO3; (PBT)] ceramic. PBT was prepared via a mixed oxide method with various PbO levels (-3, 0, 1, 3, 5 and 10 wt.%). The excess PbO was added to compensate the loss from evaporation during calcination and sintering at 800 oC and 1150 oC. It was found that lead barium titanate powders indexed in a tetragonal structure. Impurity phases of lead oxide (PbO), titanium oxide (TiO), and lead dioxide (PbO2) were detected in the calcined powders with higher than 1 wt% of excess PbO. The impurity phase was not obtained in any ceramic samples. The c/a ratios decreased with an increasing excess of PbO in both calcined powders and sintered pellets. The average particle size and the average grain size of the PBT increased with the increase of PbO. The shrinkage plots showed a maximum peak for the 1 wt.% sample which was also the most dense sample.

Influence of Firing Temperatures on Crystal Structure and Microstructure of LiNbO3 Ceramics

The effects of calcination temperature (500–800°C for 2 h) and sintering temperature (900–1025°C for 2 h) on the crystal structure and microstructure of perovskite lithium niobate (LN) ceramics were investigated. The LN ceramics were synthesized using the solid-state reaction method. The phase formation and microstructure of samples were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD results showed a single phase of LN powders which was successfully obtained using a calcination temperature of 600°C for 2 h with a heating/cooling rate of 5°C/min. With increased firing temperatures, the lattice parameter a of the calcined powders and sintered ceramics increased from 5.4912 to 5.4945 Å and 5.4952 to 5.5086 Å, respectively. The SEM result showed that the average particle size (0.31–0.39 μm) and the average grain size (0.63–2.81μm) increased with the increase of calcination and sintering temperatures, respectively. The maximum density and dielectric constant (4.46 g/cm3 and 754) were obtained from the sample sintered at 1000°C for 2 h.

Effect of Calcination Temperature and Content of x and y on Crystal Structure and Microstructure of (1-x-y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBiFeO3 Powders near MPB Prepared via the Combustion Technique

(1-x-y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBiFeO3 (abbreviated as BNKFT-x/y with 0.12 ≤ x ≤ 0.24, 0 ≤ y ≤ 0.07) lead-free piezoelectric powders were prepared by the combustion technique under various calcinations temperatures (600–800°C) for 2 h. The effect of calcination temperature and amounts of x and y on the crystal structure and microstructure were examined. The powders of all samples were well-calcined at 750 C°. The results indicated that there was an increase in the x and y concentrations of the crystalline structure and microstructure. XRD results of the BNKFT-x/0.03 and BNKFT-0.18/y ceramics with 0.12 ≤ x ≤ 0.24 and 0 ≤ y ≤ 0.07 showed the pure perovskite phase with a rhombohedral structure. The lattice parameter a increased from 3.8517 Å to 3.8696 Å and 3.8550 Å to 3.8623 Å with increasing x and y content, respectively. The SEM and TEM results indicated that the addition of y caused the particles to grow (from 291 nm to 308 nm) while the addition of x reduced particle growth (from 390 nm to 277 nm).

The Effect of Excess PbO on Crystal Structure, Microstructure and Dielectric Properties of (Pb0.50Sr0.50)TiO3 Ceramics

Lead strontium titanate [(Pb50Sr50)TiO3; PST] ceramics were fabricated by the conventional solid state reaction method using calcination and sintering temperatures of 950°C and 1250°C. To prevent PbO evaporation during the firing processes, excess PbO was added to the samples in varying amounts from 0–10 wt.%. It was found that PST powders indexed in a tetragonal structure. Impurity phases were detected in the calcined powders which had excess PbO higher than 3 wt%. A pure perovskite phase was obtained from all ceramic samples. The lattice parameters a, c and the c/a ratio decreased with an increasing excess of PbO. The average particle size and the average grain size increased with the increase of PbO. The porous microstructure slightly decreased with an increasing amount of PbO, up to 1 wt.%, then slightly increased with higher excess PbO. The density can be improved by adding 1 wt.% of excess PbO. The dielectric constant increased from 7500 for the 0 wt.% sample to 8300 for the 1 wt%. This was followed by reductions for 3, 5 and 10wt.%. The Curie temperature and transition enthalpy slightly increased with an increase amount of PbO until 1 wt.%, then slightly decreased, for the higher excess PbO.