Theerachai Bongkarn

THE STRUCTURAL PHASE AND MICROSTRUCTURES OF PEROVSKITE Ba(Ti1-xZrx)O3 CERAMICS USING THE COMBUSTION ROUTE

Ba(Ti1-xZrx)O3; BTZ (x = 0.20 and 0.25) ceramics are attractive candidates for dynamic random access memories, tunable microwave devices and capacitors. In this study, the preparation of BTZ powders and ceramics fabricated by the combustion method were studied in detail. The calcination and sintering conditions were performed from 600 to 900°C for 4 h and from 1300 to 1450°C for 2 h, respectively. The highest percentage of the cubic perovskite phase was found in the powders that were calcined at 800°C. A pure cubic perovskite structure was found in all ceramic samples. The average grain size increased with increasing sintering temperatures. Dielectric constant-temperature plots showed a maximum peak value of 7500 and 8300 for x = 0.20 and 0.25. The phase transition temperature of the BTZ ceramics occurred at 30°C and 10°C for x = 20 and 25, respectively.

Phase Formation and Microstructure of Barium Zirconate Ceramics Prepared Using the Combustion Technique

The effect of calcination temperatures (900–1400°C) and sintering temperatures (1400–1650°C) on phase formation and microstructure of perovskite barium zirconate (BaZrO 3 ) powders and ceramics was investigated. The BaZrO 3 powders were prepared using the combustion technique. The phase purity, crystal structure and microstructure of samples were examined using differential thermal analysis (DTA), thermo gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that BaZrO 3 samples indexed in a cubic structure. The percentage phase purity of perovskite increased with an increase in the calcination temperatures as expected. The purity of perovskite powders was obtained above 1350°C and the purity phase of ceramics was detected in all samples. The SEM results indicated that the particle size and grain size of samples increased with the increase of calcination and sintering temperatures. The shrinkage of ceramics increased as the sintering temperatures increased. The optimized heat treatment permits sintering a ∼97% highly dense barium zirconate sample at 1600°C for only 2 h.

Fabrication of Perovskite Barium Titanate Ceramics Using the Combustion Route

The phase formation and microstructure of barium titanate (BT) perovskite fabricated using the combustion route was observed. (CO(NH 2 ) 2 ) was used as a fuel to decrease the reaction temperature. Pure perovskite BT powders were obtained at calcination temperatures above 1200°C. The a parameter decreased while the c parameter increased with increasing calcination temperatures. The average particle size increased from 90 to 590 nm with an increase of calcination temperature. The pure tetragonal perovskite structures were found in all BT ceramics. The densest of the BT ceramics were obtained with a sintering temperature of 1300°C. The dielectric constant at room temperature was also observed.

Fabrication and Characterization of Perovskite SrZrO3 Ceramics through a Combustion Technique

Perovskite SrZrO3 ceramics were successfully prepared via a combustion technique. The effect of calcination temperatures (900-1400oC) and sintering temperatures (1400-1650oC) on phase and morphology evolution of perovskite SrZrO3 ceramics were studied. The highest purity of perovskite phase powder was obtained at 1250 oC and the purity of the perovskite phase of SrZrO3 ceramics were detected in the samples sintered at 1550 oC for 6 h. The SEM results showed the average particle size (84-214 nm) and the average grain size (0.35-2.09 µm) of samples increased with the increase of firing temperatures. The shrinkage of the ceramics increased as the sintering temperatures increased. The maximum density was ~98.4% of the theoretical density for the sample sintered at 1550 oC for 6 h.

Low Firing Temperatures and High Ferroelectric Properties of (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Lead-Free Ceramics Synthesized by the Combustion Technique

This work studied the effect of firing conditions on phase formation, microstructure and electrical properties of (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3;(abbreviated as BCTZ) ceramics, which were synthesized through the combustion technique. To reduce the reaction temperature, glycine was used as fuel with a ratio of raw material: glycine (1:1.11). BCTZ samples were calcined at 900–1200°C for 2 h and sintered at 1350 –1550°C for 2 h. Ultrafine BCTZ powder and single peroveskite phase were achieved from the sample calcined at 1050°C for 2 h.These results were obtained at a lower temperature and with shorter dwell time than those obtained using the solid state reaction method by ∼150°C and 1 h, respectively. The BCTZ ceramics exhibited a coexistence of rhombohedral and orthorhombic phase in all samples. The average particle size and the average grain size increased from 172 to 295 nm and 0.82 to 2.57 µm, respectively, when firing temperatures increased. The highest density (5.76 g/cm3), highest dielectric constant (ϵr ≅ 4485 and ϵmax ≅ 14897) and best ferroelectric properties (Pr ≅ 18.47 μC/cm2 and EC ≅ 4.52 kV/cm) were obtained from the sample sintered at 1450°C for 2 h.

Effect of Firing Temperatures on Phase and Morphology Evolution of CaZrO3 Ceramics Synthesized Using the Combustion Technique

The effects of calcination temperatures (900–1400°C) and sintering temperatures (1400–1650°C) on phase and morphology evolution of perovskite CaZrO3 ceramics were studied. The results obtained from DTA-TGA analysis were used to determine the processed conditions of various calcination temperatures. The highest purity of the orthorhombic perovskite phase was obtained from powder calcined at 1200°C and the pure phase was detected in sintered ceramic samples below 1650°C. The SEM results showed that the average particle size and the average grain size of samples increased with the increase of firing temperatures. The shrinkage of ceramics increased as the sintering temperatures increased. The calcium zirconate, which had around 97.6% of the theoretical density, was obtained from the sample sintered at 1500°C for 2 h. More importantly, the highest density with low sintering temperature were be improved by the combustion technique.

Low Temperature Preparation of Antiferroelectric PZ and PBZ Powders Using the Combustion Technique

Lead zirconate, PbZrO 3 (PZ) and lead barium zirconate, (Pb 0.90 Ba 0.10 )ZrO 3 (PBZ), powders were prepared by a combustion technique under various calcination temperatures (600°C – 1000°C). (CO(NH 2 ) 2 ) was used as a fuel to reduce the reaction temperature. The crystalline structure of PZ and PBZ powders was analyzed by X-ray diffractometer (XRD). It was found that the purity of the perovskite phase of PZ and PBZ was obtained with a calcination temperature at 800°C. The result corresponded to the DTA-TGA results. The calcination temperatures affected phase formation but not the microstructure.

Optimum Sintering Temperature for Fabrication of 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3 Lead-Free Ceramics by Combustion Technique

The effect of sintering temperatures (1050-1200 °C) on the phase formation, microstructure and dielectric properties of a binary system lead-free ceramic bismuth sodium titanate–bismuth potassium titanate were investigated. 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3; BNKT ceramics were successfully fabricated using the combustion technique. XRD results showed the rhombohedral-tetragonal morphotropic phase boundary (MPB). The SEM results showed the average grain size (0.51-2.59 µm) of the samples increased with the increase of sintering temperatures. The sample sintered at the optimum temperature of 1150 °C exhibited the maximum density, shrinkage, dielectric constant at Curie temperature and remanent polarization (Pr) which were around 5.65 g/cm3, 17.75%, 5014 and 1.6 mC/cm2, respectively. The dielectric constant was related to the XRD results and density of the sintered ceramic.

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 transition and linear thermal expansion of (Pb1− x Ba x )ZrO3 ceramics

(Pb1− x Ba x )ZrO3 ceramics for the composition range 0 ≤ x ≤ 0.30 were prepared by the mixed oxide solid state reaction method. Phase transition was studied by dielectric and dilatometric measurements. The ferroelectric to paraelectric phase transition temperature was progressively shifted to a lower temperature by replacing lead with barium. The x = 0.20 sample showed the maximum dielectric constant of 16,300 at the transition temperature. For compositions 0 ≤ x ≤ 0.075, the antiferroelectric to ferroelectric phase transition exhibited a large linear thermal expansion. However, the antiferroelectric to ferroelectric phase transition did not exist for 0.10 ≤ x ≤ 0.30 samples. A phase diagram for PBZ ceramics prepared by the conventional mixed oxide method was also present.