Nuttapon Pisitpipathsin

Morphotropic Phase Boundary of Lead-Free Piezoelectric Ceramics from BNT- KN System

In this research work, the investigation of the morphotropic phase boundary, physical properties and electrical properties of lead- free piezoelectric materials of bismuth sodium titanium oxide: (Bi0.5Na0.5)TiO3 (BNT) and potassium niobium oxide : KNbO3 (KN) in the ceramic system of (1-x)BNT- xKN where x= 0.00, 0.03, 0.05, 0.08, 0.10 and 0.15 by modified mixed oxide method was carried out. The BNT and KN powders were prepared separately using calcination technique with optimum calcination temperature for producing both BNT and KN powders of about 800°C. XRD results revealed that the BNT-KN ceramics with low KN content of x less than 0.05 contain ferroelectric perovskite phase with rhombohedral symmetries while the higher KN content ceramics have mixed symmetries between rhombohedral and orthorhombic. From the evidences including phases, microstructures and dielectric data of the BNT-KN ceramics, it may be assumed that the morphotropic phase boundary may be at around the composition of x = 0.05.

Microstructure and electrical properties of BaFe 0.5Nb 0.5O 3 Doped with GeO 2 (1-5 wt.%)

In this work, the effects of GeO2 dopant on the electrical properties of BaFe0.5Nb0.5O3 (BFN) perovskite ceramics were investigated. The BFN powder was prepared by a conventional mixed-oxide method using stoichiometric amounts of BaCO3, Fe2O3 and Nb2O5. Afterward the GeO2 contents, ranging from 1 to 5 wt.%, were added to the calcined BFN powder and mixed via vibro-milling method. The mixtures were pressed and sintered at 1125–1150°C for 4 h to form dense ceramics. We showed that the addition of GeO2 caused a reduction of grain size and formation of secondary phases: Ba3Fe2Ge4O14 and BaGeO3. The maximum densities of these BFN doped with GeO2 ceramics were slightly lower than those of the pure BFN due to the occurrence of pores. We also found that the GeO2 doping could improve the dielectric properties of these ceramics at room temperature (25°C). The 1 wt.% GeO2 doped sample exhibited higher dielectric constant of about 1800 and lower dielectric loss of 0.45 comparing to that of pure BFN. However, the dielectric constant values of these ceramics at high temperature (>25°C) were decreased significantly with the increase of GeO2 concentration. In addition, the GeO2 additive gave a weak ferroelectric behavior, leading to change in the pyroelectric coefficient and spontaneous polarization of the GeO2 doped BFN ceramics.

Dielectric properties of lead-free solid solution of Bi0.487Na0.487La0.017TiO3 and BaTiO3

Bismuth sodium titanate (Bi0.5Na0.5TiO3; BNT) is one of the most preferred materials for the preparation of lead-free ceramics; however its dielectric property is lower than that of lead-based materials. Thus, the substitution of A and B-site cations is considered to be one of the best solutions in order to improve both the dielectric and piezoelectric properties. In this study, lead-free ceramics from bismuth sodium lanthanum titanate (Bi0.487Na0.487La0.017TiO3; BNLT) and barium titanate (BaTiO3; BT) systems were prepared by a modified two-step mixed oxide method. BT powder was added to BNLT powder with the desired compositions of (1 − x)BNLT–xBT, where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10. It was found that the addition of BT in the BNLT improved the electrical properties of ceramics. Phase transition of rhombohedral to tetragonal structure was significantly dependent on the amount of BT added. It was also found that the change in crystal structure affected the ferroelectric property of the ceramics where the transition from ferroelectric to antiferroelectric started from the samples with x ≥ 0.06 mol% and higher. This may be useful in terms of using these materials in the desired applications.

Effect of BaZr0.05Ti0.95O3 Addition on Microstructure and Piezoelectric Properties of Hydroxyapatite Bone

The aim of this study was to investigate the effect of BaZr0.05Ti0.95O3 (BZT) addition on the microstructure, physical, dielectric and piezoelectric properties of hydroxyapatite (HA), and develop new biomaterials which have potential applications in the support for cellular growth and in the system for bone regeneration. In this case the BaZr0.05Ti0.95O3- HA composites (HABZT) were prepared by conventional sintering method. The BZT were added to HA with ratio 0, 10, 20 and 30 %wt. Then the mixed powders were pressed and subsequently sintered at the temperature ranging from 1150 to 1350°C. The result showed that the dielectric and piezoelectric properties were improved by the addition of BZT. Moreover, the bioactivity of the HA improved with addition of BZT especially at 10% as evident by the formation of bone like apatite layers on the surface of all BCZT composites after soaking in simulated body fluid (SBF) for 15 days. The results confirmed the possibility of using these bioactive composites for treatment within the human body.

Enhanced electrical properties of lead-free Bi2GeO5 ferroelectric glass ceramics by thermal annealing

To study the effect of thermal annealing on the electrical properties of lead-free Bi2GeO5 ferroelectric glass ceramics, the glass ceramics with composition of Bi2GeO5 were prepared by the conventional melt-quenching and heat-treatment methods subsequently. Glass ceramics of Bi2GeO5 was produced by subjecting the glasses from BiO1.5-GeO2-BO1.5 system to the heat treatment schedule at 475°C for 18 h. After that, the resulting samples were separately annealed at 275 and 375°C for 4, 8, 12 and 18 h, respectively. The important properties of the annealed Bi2GeO5 glass ceramics such as physical properties, phase formation and electrical properties were then investigated. It was found that the annealing treatment played an important role on electrical properties of these glass ceramics. The XRD patterns confirm the secondary phase of Bi4Ge3O12 co-existed with Bi2GeO5 which increased at higher annealing temperature and time. This caused a change in density and related electrical properties of the Bi2GeO5 glass ceramics. Both annealing temperature of 275 and 375°C with various times can improve dielectric properties and ferroelectric behavior of the resulting Bi2GeO5 glass ceramics when comparing with that of un-annealed sample. The optimum annealing temperature and time for the improvement of dielectric properties of Bi2GeO5 glass ceramics was found at 375°C/12 h, where the maximum values of the dielectric constant (ϵr) of 246 and low dielectric loss (tanδ) of 0.024 were obtained. Moreover, the ferroelectric property of all annealed glass ceramics exhibited the slim P-E loop and Pr values which slightly increased with increasing annealing temperature and time. However, the P-E loops are not the feature of truly ferroelectric, it may be represent a lossy capacitor behavior.

Phase Transition and Dielectric Properties of PNNZT-BNLT Ceramics

The (1−x)Pb(Ni0.33Nb0.67)0.5Ti0.35Zr0.15O3[PNNZT] – xBi0.4871Na0.4871La0.0172TiO3[BNLT] ceramics (x = 0, 0.03, 0.06, 0.09, 0.12 and 0.15) were prepared by a two steps mixed-oxide method. XRD patterns of all ceramic samples exhibited a complete perovskite phase without pyroclore and no second phase. The BNLT addition has a significant effect on the grain growth inhibition of PNNZT-BNLT ceramics. The dielectric studies indicated that the phase transition behavior of the ceramic compositions becomes more diffuse with increasing BNLT content. The addition of BNLT content caused the increase in Tm, for example: about 16% for the 0.03 mol% BNLT sample while tanδ was reduced to about 60% compared with that of pure PNNZT sample.

Effect of BCZT on Electrical Properties and Bioactivity of 45S5 Bioglass

In this work, ferroelectric Ba0.92Ca0.08Zr0.05Ti0.95O3/45S5 bioglass composite or (BCZT/45S5 composite) has been produced for orthopedic applications. The BCZT concentrations ranged from 0–15 wt.%. The BCZT/45S5 composite was prepared by conventional melting method at 1300°C for 1 h following by heat treatment schedule at the crystallization temperatures of glass. The effects of BCZT addition on the dielectric and piezoelectric properties and the biocompatibility of BCZT/45S5 composites were investigated. It was found that, the addition of BCZT improved the hardness and dielectric properties of materials, which may be caused by the presence of the BCZT. Moreover, the bioactivity of the 45S5 bioglass was improved with addition of BCZT phase as evident by the formation of bone like apatite layers on the surface of all BCZT/45S5 composites after soaking in simulated body fluid (SBF).

Piezoelectric and Ferroelectric Properties of KNbO3 Added Bi0.5Na0.5TiO3 Ceramics

The fabrication of lead-free (1-x)Bi0.5Na0.5TiO3 - xKNbO3 or (1-x)BNT-xKN ceramics where x = 0.00, 0.05, 0.10, and 0.15 was carried out by the modified two-step mixed oxide method. The effects of KNbO3 on structure, piezoelectric and ferroelectric properties were systematically investigated. XRD results revealed that the (1-x)BNT-xKN ceramics with low KN content of x less than 0.05 contained ferroelectric phase with a rhombohedral symmetry while the ceramics with x = 0.05 possessed pseudocubic structure. The higher KN content (x ≥ 0.10) ceramics had symmetries rhombohedral structure. At room temperature, the highest Pr and low Ec were obtained when the composition of x = 0.05. Moreover, the results showed the moderate KN addition could enhance the piezoelectric response. The d33 of 0.95BNT-0.05KN reached as high as 125 pC/N.

Dielectric Relaxation and Electrical Properties of Lead-Free Perovskite BaGex(Fe0.5Nb0.5)1−xO3 Ceramic

The lead-free BaGex(Fe0.5Nb0.5)1−xO3: BGFN ceramics were synthesized by a solid state reaction technique. The BGFN powders were produced via mixed-oxide method with the desired compositions of BaGex(Fe0.5Nb0.5)1-xO3 where x = 0.01, 0.015, 0.02 and 0.025, respectively and subsequently calcined at different temperatures from 1100 to 1200°C for 4 h. The mixtures were pressed in to pellets and sintered at 1200 to 1350°C for 4 h to form dense ceramics. The characteristics, including phase formation, microstructures, dielectric properties and pyroelectric properties were also investigated. It was observed that the Ge4+ cations played an important role on the change of crystal structures and the phase formation of the BGFN phases. The XRD results indicated that the structure of BFN is cubic and transforms to monoclinic when the Ge concentration is over 0.015. Moreover, the higher level of Ge4+ addition caused a reduction of grain size and formation of secondary phases: Ba3Fe2Ge4O14 and BaGeO3. The amount of each phase was depended on the concentration of Ge where the Ba3Fe2Ge4O14 and BaGeO3 phases were found to increase with increasing of x content. This in turn affected their electrical properties where dielectric constant (ϵr) was dominately decreased while the dielectric loss and the pyroelectric properties were greatly improved. The optimum composition for this system was found to be x = 0.01, where the maximum values of dielectric constant (∼12000) with relatively lower dielectric loss (0.95) at 1 KHz and at room temperature were achieved. The change in the pyroelectric coefficient and spontaneous polarization of the BFN ceramic is possibly due to the segregation of Ge4+ at grain boundary, resulting in resistance to domain switching during heating or cooling the sample. This promises a good candidate for the new lead free ceramic for applications in capacitors.

Electrical Properties of Calcium Phosphate/BZT Bioglass-Ceramics Prepared by Incorporation Method

Electrically active bioglass has received much attention as artificial bone graft material. In this study, the dielectric and piezoelectric properties of calcium phosphate-barium zirconium titanate bioglass-ceramics (CPGs-BZT bioglass-ceramics) were investigated as a function of BZT content. The BaZr0.05Ti0.95O3–40CaO-45P2O5–15Na2O bioglass (CPGs/xBZT where x = 0, 10, 20, 30, 40, 50 wt.%) was prepared by an incorporation method. Crystallization temperature of each glass was measured by differential thermal analysis (DTA). XRD and SEM techniques were also used to characterize the phase formation and microstructure. The results showed that the BZT content caused an increase in dielectric and piezoelectric properties. The bioactivity of BZT/CPGs bioglass-ceramics was found to be higher than that of the pure CPGs after soaking in SBF for 14 days.