การประดิษฐ์เซรามิกเฟร์โรอิเล็กทริกไร้ตะกั่วในระบบบิสมัทโซเดียมโพแทสเซียมไททาเนตเป็นองค์ประกอบหลัก

รายงานวิจัย -- มหาวิทยาลัยเทคโนโลยีราชมงคลพระนคร, 2561The research project investigated the effects of CoO additive on dielectric, ferroelectric, physical and mechanical properties of modified Bi0.5(Na0.81,K0.19)0.5TiO3 ceramics were investigated. The samples were synthesized by solid state reaction technique, where powders were calcined at 850 °C for 4 h and ceramics were sintered at 1,050 °C for 4 h which difference heating rate controlled i.e. 100, 300, and 600 °C/h for. The ceramics of BNKT/x wt.% CoO was added CoO by various x=0.00, 0.10, 0.20, 0.30, 0.60 and 0.90. Phase formation was determined by X-ray diffraction technique (XRD). The X-ray diffraction analysis of the ceramics suggests that all samples exhibited a perovskite structure. The dielectric properties under room temperature and various temperatures were also determined. Dielectric measurement data showed that the additive and heating rate controlled influenced dielectric constant and dielectric loss. Furthermore, the hysteresis loop behaviors slightly changed with increasing the CoO contents.Rajamangala University of Technology Phra Nakho

Lead-free piezoelectric K0.5Bi0.5TiO3–Bi(Mg0.5Ti0.5)O3 ceramics with depolarisation temperatures up to ~220 C

The properties of K0.5Bi0.5TiO3-rich ceramic solid solutions in the system (1 - x)K0.5Bi0.5TiO3– xBi(Mg0.5Ti0.5)O3 are reported. The highest values of piezoelectric charge coefficient, d33, and field-induced strains are found in compositions located close to a compositional boundary between single-phase tetragonal and mixed tetragonal ? cubic perovskite phases. Maximum d33 values were *150 pC/N for x = 0.03, with positive strains of *0.25 %; the x = 0.04 composition had a d33 * 133 pC/N and strain of 0.35 % (bipolar electric field, 50 kV/ cm, 1 Hz). Depolarisation temperature Td is an important selection criterion for any lead-free piezoelectric for actuator or sensor applications. A Td of *220 C for x = 0.03 is *100 C higher than for the widely reported Na0.5Bi0.5TiO3–BaTiO3 system, yet d33 values and strains are similar, suggesting the new material is worthy of further attention as a lead-free piezoceramic for elevated temperature applications

High temperature dielectric ceramics: a review of temperature-stable high-permittivity perovskites

Recent developments are reviewed in the search for dielectric ceramics which can operate at temperatures >200 °C, well above the limit of existing high volumetric efficiency capacitor materials. Compositional systems based on lead-free relaxor dielectrics with mixed cation site occupancy on the perovskite lattice are summarised, and properties compared. As a consequence of increased dielectric peak broadening and shifts to peak temperatures, properties can be engineered such that a plateau in relative permittivity–temperature response (εr–T) is obtained, giving a ±15 %, or better, consistency in εr over a wide temperature range. Materials with extended upper temperature limits of 300, 400 and indeed 500 °C are grouped in this article according to the parent component of the solid solution, for example BaTiO3 and Na0.5Bi0.5TiO3. Challenges are highlighted in achieving a lower working temperature of −55 °C, whilst also extending the upper temperature limit of stable εr to ≥300 °C, and achieving high-permittivity and low values of dielectric loss tangent, tan δ. Summary tables and diagrams are used to help compare values of εr, tan δ, and temperature ranges of stability for different material

Temperature-Stable Dielectric Ceramics based on Na₀.₅Bi₀.₅TiO₃

Multiple ion substitutions to Na0.5Bi0.5TiO3 give rise to favourable dielectric properties over the technologically important temperature range −55 °C to 300 °C. A relative permittivity, εr, = 1300 ± 15% was recorded, with low loss tangent, tanδ ≤ 0.025, for temperatures from 310 °C to 0 °C, tanδ increasing to 0.05 at −55 °C (1 kHz) in the targeted solid solution (1–x)[0.85Na0.5Bi0.5TiO3–0.15Ba0.8Ca0.2Ti1-yZryO3]–xNaNbO3: x = 0.3, y = 0.2. The εr-T plots for NaNbO3 contents x < 0.2 exhibited a frequency-dependent inflection below the temperature of a broad dielectric peak. Higher levels of niobate substitution resulted in a single peak with frequency dispersion, typical of a normal relaxor ferroelectric. Experimental trends in properties suggest that the dielectric inflection is the true relaxor dielectric peak and appears as an inflection due to overlap with an independent broad dielectric peak. Process-related cation and oxygen vacancies and their possible contributions to dielectric properties are discussed

Influence of Al2O3 Nanoparticles’ Incorporation on the Structure and Electrical Properties of Pb0.88Sr0.12Zr0.54Ti0.44Sb0.02O3 Ceramics

In this research, the effects of an Al2O3 nanoparticle additive on the structure and electrical properties of Pb0.88Sr0.12Zr0.54Ti0.44Sb0.02O3 (PSZST) ceramics were investi‐ gated. The PSZST ceramics with the addition of 0 - 2.0 vol % Al2O3 were fabricated via a solid-state mixed oxide method and sintering at 1250°C for 2 h to obtain dense ceramics. X-ray diffraction indicated that all compositions exhibited a single perovskite structure. Phase identification showed coexisting mixed rhombohedral and tetragonal phases for the modified ceramics, while the unmodified ceramics showed a rhombohedral-rich phase. The addition of Al2O3 nanoparticles was also found to improve the densification and the electrical properties of the PSZST ceramics, such as dielectric constant and polarization. The 2.0 vol% sample showed the highest low-field piezoelectric coefficient (d33) value of 646 pC/N, which was 90% higher than that of the unmodified sample, suggesting that this composition had the potential to be one of the promising piezoelectric ceramic candidates for further use in actual applications

Low variation in relative permittivity over the temperature range 25-450°C for ceramics in the system (1-x)[Ba0.8Ca0.2TiO3]-x[Bi(Zn0.5Ti0.5)O3]

The dielectric and ferroelectric properties of the ceramic system, (1-x)Ba0.8Ca0.2TiO3-xBi(Zn0.5Ti0.5)O3, were investigated for compositions 0≤x≤0.4. X-ray powder diffraction patterns indicated tetragonal symmetry at x≤0.05, switching to pseudocubic at x≥0.1, with a single-phase solid solution limit at 0.2<x<0.3. The x=0 and 0.05 samples were ferroelectric; a change to relaxor behaviour occurred at x≥0.1, with broad frequency dependent peaks in plots of relative permittivity versus temperature. A significant reduction in the temperature dependence of relative permittivity occurred at x=0.3, with e{open};r=1030±15% over the temperature range ~25-425°C, and loss tangent, tanδ≤0.01 from 110°C to 420°C. The dc resistivity values for x=0.3 were ~109Ωm at 300°C and ~106Ωm at 450°C