Papers by Keyword: BNKT

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Authors: Pin Yi Chen, Cheng Sao Chen, Chen Chia Chou, Tseung Yuen Tseng, Haydn Chen
Abstract: Second phase and defect formation mechanism of (Bi0.5(Na1-xKx)0.5)TiO3 (BNKT100x) ceramics were investigated using electron microscopy, x-ray photoelectron spectroscope (XPS) and electrical properties measurements. Experimental results indicated that second phase formation induces Bi-rich regions and compositional inhomogeneity within matrix due to thermodynamic stability of potassium titanate. Ti valence transition for BNKT ceramics sintered in air might be ascribed to formation of the secondary phase, rather than simply attributed to volatilization of bismuth. Li substitution at A-site in BNKT ceramics suppresses formation of the second phase and Ti valence transition. Appropriate Li doped BNKT ceramics suppress oxygen vacancies and titanium valence transition, and therefore decrease the leakage current.
Authors: Supalak Manotham, Pichitchai Butnoi, Narumon Lertcumfu, Pharatree Jaita
Abstract: This research investigated the effects of sintering temperatures on the structural, dielectric, ferroelectric, piezoelectric and mechanical properties of lead-free Bismuth Sodium Potassium Titanate (BNKT) piezoelectric ceramics. The BNKT ceramics were prepared by solid-state mixed oxide method and sintering at temperature ranging from 1100 to 1150°C for 2 h. All ceramics sample showed highly density and reach a maximum at sintering temperature 1125°C of 5.81 g/cm3. X-ray diffraction patterns exhibited pure perovskite structure with coexisting of rhombohedral-tetragonal phases for all compositions. The microstructure was characterized by Scanning Electron Microscope (SEM), from SEM image the ceramics showed cubic-like grain shape. The average grain size increased with increasing sintering temperature. The dielectric permittivity showed the optimum sintering at 1125°C with reach a maximum dielectric constant of 4,194. Furthermore, at sintering temperature 1125°C present highest strain (Smax = 0.14%) with a large normalized strain coefficient (d*33 = Smax/Emax) of 233 pm/V.
Authors: Atthakorn Thongtha, Theerachai Bongkarn
Abstract: 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.
Authors: Supalak Manotham, Pichitchai Butnoi, Pharatree Jaita, Tawee Tunkasiri
Abstract: In this work, the properties of lead-free 0.92(Bi0.5Na0.42K0.08)TiO3-0.08(BaNb0.01Ti0.99)O3 or 92BNKT-8BNbT ceramic has been investigated. The sample was fabricated by a solid-state reaction technique. The 92BNKT-8BNbT sample was well sintered and dense with high density value of 5.86 g/cm3. X-Ray diffraction (XRD) patterns showed a single perovskite phase with tetragonal symmetry and no impurity or secondary phases. The microstructure was analysed using a scanning electron microscopy (SEM). Average grain size was measured and calculated based on a mean linear intercept method. The ceramics had a cubic-like grain shape with an average grain size of 0.39 µm. The influence of temperature on the dielectric and ferroelectric properties of the ceramic was investigated. The dielectric curves exhibited broad transition peaks at Td and Tm, which were the characteristics of a diffuse phase transition. The polarization-electric field (P-E) hysteresis loop changed from well-saturated at room temperature (RT) to pinched-type loop at high temperature (HT) and the remanent polarization decreased from 21.25 µC/cm2 (at RT) to 5.96 µC/cm2 (at 150 °C).
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