Denis Russell Sweatman

Preparation and Electrical Behaviour of BaCeO3 Ceramics

Barium cerate (BaCeO3) ceramics were synthesized via a solid-state reaction technique. Pure phase perovskite powders were obtained at a calcination temperature of 1200 °C. BaCeO3 ceramics were fabricated from the calcined powder and their properties were investigated. XRD data of the ceramics was consistent with an orthorhombic symmetry. However, the pure phase perovskite of the BaCeO3 ceramics was only observed for sintering temperatures less than 1500°C. The microstructural analysis indicated that grain sizes of the ceramics increased with increasing sintering temperature. The dielectric constant of the samples had a constant value over a very wide range of temperature. All ceramics showed very good dielectric performance where the ceramics sintered at 1450 °C showed the highest dielectric constant.

Phase Formation and Grain Growth of BSCZT Ceramics Prepared by BST-BZT Seed Induced Method

In this work, lead-free Ba0.4Sr0.4Ca0.2Zr0.05Ti0.95O3 ceramics were prepared by the seed induced method using (0.5Ba0.6Sr0.4TiO3–0.5BaZr0.05Ti0.95O3) (BST-BZT) seed. Seed crystals with concentrations of 0, 2.5, 5, 7.5, 10 mol% were mixed with BSCZT powder for 24 h and sintered at 1400 °C for 4 h. The phase formation and microstructure of BSCZT ceramic were characterized by X-ray diffraction technique (XRD) and the scanning electron microscopy (SEM). All samples showed a single phase perovskite structure without impurities and exhibited the existence of the tetragonal phase. The density values of the ceramics decreased from 4.90 to 4.75 g/cm3 with increasing seed crystal concentrations. The grain size of the sample without seed was 3.71 μm, whereas a grain size of 8.99 μm was observed for the sample with 10 mol% seed crystal. The dielectric constant at room temperature at 1 kHz was 1831 for the sample with 10 mol% seed crystal while the dielectric constant of the sample without seed was 1484. From the results in this work, BST-BZT seed can increase grain size and improve the dielectric constant at room temperature.

The mechanical and electrical properties of modified-BNKT lead-free ceramics

ABSTRACT This research was conducted to study influence of ferric oxide nanoparticles on the properties of modified BNKT ceramics. The optimum sintering temperature was 1125°C at which all compositions had low porosity (0.12–0.19%). Raman and XRD showed coexisting rhombohedral and tetragonal phases throughout the entire compositional range. The Pr, d33 and g33 were slightly degraded when the additive was added. The maximum room temperature dielectric (ϵ′ = 1689, tan δ = 0.0606) and mechanical properties (HV = 5.6 GPa, HK = 4.9 GPa, E = 93 GPa and KIC = 1.58 MPa.m1/2) was obtained for the 2 vol% sample.

Electric field–induced strain behavior and ferroelectric properties of lead zirconate titanate-barium calcium zirconate titanate ceramics

ABSTRACT In this work, electric field-induced strain behavior and ferroelectric properties of xBCZT/PZT (with x = 0, 4 and 8 mol%) ceramics have been investigated. The Ec and Pr increased with increasing electric field and exhibited pinched-shape hysteresis loop at 60 kV/cm. The abnormal domain walls and switching behavior of the domains were used to discuss the above results. The strain value increased with increasing BCZT content and reached the maximum value of 0.27% (d*33 = 450 pm/V) for the 4 mol% BCZT sample. This offered an opportunity to obtain a good candidate for using in piezoelectric applications.

Electrical properties of sodium potassium niobate/mullite ceramic composites

ABSTRACT In the present study, the composites between KNN and mullite were fabricated via a solid-state reaction technique. KNN was calcined at 900°C and mullite which synthesized from kaolinite (Ranong, Thailand) was calcined at 1300°C. Effects of KNN content on the composites properties such as densification and electrical properties including dielectric, ferroelectric and piezoelectric properties have been investigated. It was found that the densification behavior of the composites was improved by KNN added. The addition of KNN also resulted in improvements of electrical properties such as remanent polarization, dielectric constant, and piezoelectric coefficient of the materials.

Electrical Properties of Modified BNT Based Lead-Free Ceramics

The properties of modified Bi0.5Na0.5TiO3 (BNT) based lead-free ceramics were investigated. The BNT-based ceramics were prepared by a solid-state mixed oxide method Phase formation was determined by X-ray diffraction technique (XRD). The X-ray diffraction analysis of the ceramics suggested that all samples exhibited a perovskite structure without second phase. The value of dielectric constant increased with increasing in sintering temperature. Moreover, high sintering temperatures could improve ferroelectric properties of BNT base lead-free ceramics.

Effect of Electrode on Electrical and Ferroelectric Behavior of Modified BNT Lead-Free Ceramics

In this research, the effect of electrode type on electrical i.e. dielectric and ferroelectric behavior of 0.94BNT-0.06BT ceramics was studies. The ceramics were prepared by conventional mixed oxide method. The sample exhibited a pure perovskite structure with rhombohedral phase. For dielectric measurement, the ceramics with Ag pasted electrodes exhibited very high dielectric constants and good responding with low frequency than Au sputtered electrode.

Electrical Properties of BNKTZ Ceramics as a Function of Calcination Temperature

In this research, the Bi0.5(Na0.80K0.20)0.5Ti0.99Ti0.10O3 were prepared via a conventional solid-state reaction method, and their properties were related with calcination temperature. The crystalline structure of BNKTZ ceramics was assessed by X-ray diffraction (XRD) method. Other physical properties, i.e. porosity, density, microstructure, and electrical properties were determined. XRD patterns for all samples showed a pure perovskite, where coexistence between rhombohedral and tetragonal phases was observed for some conditions. The optimum dielectric constant was obtained for the ceramic calcined at 800 °C. The ferroelectric and piezoelectric properties were improved and showed the highest values for the calcination temperature around 900-1000°C. The improvements of ferroelectric and piezoelectric properties were proposed to be due to the ceramics had compositions closed to MPB composition. Furthermore, density also had a contribution for the improvements.

Fabrication and Properties of Mullite Ceramics from Ranong Kaolin

In the present study, mullite powders were prepared from fired Ranong kaolin powder at high temperatures. Differential thermal analyses and X-ray diffraction (XRD) technique were used to understand kaolin–mullite reaction sequence and phase formation of the starting material after a heat treatment, respectively. It was found that phase of mullite started to occure at ∼1000 °C. Microstrural study by a scanning microscope, indicated that there was a change in microsture after the heat treatment, i.e. grain shape changed from equiaxed to needle grains shape . The AC conductivity decreased with decreasing the sintering temperature and 1500 °C ceramic presented a very high frequency stabilty of conductivity, suggesting that this martial can be used as an electrical insulator for wide frequency range.

Influence of Curing on Calcined Kaolin-Based Geopolymer

The object of this work was to use calcined kaolin-based geopolymer as an alternative material to replace ordinary Portland cement (OPCs) by applying geopolymerization processes. Geopolymer slurry was prepared from calcined kaolin and alkali activators, which consisted of 10 M NaOH and Na2SiO3 solution. The fresh slurry was cast into plastic molds and then cured at room temperature for 24 h. Reaction temperatures were measured (for 24 hours after casting). Compressive strength of the geopolymer was tested after curing at room temperature and after microwave heating. The mechanical properties increased with added plaster for microwave curing of 5 min. It is believed that this process can increase the efficiency of the production line for geopolymer.