Preparation and ferroelectric properties of MnO2 doped BaTi2O5 ceramics by spark plasma sintering from the solid-state-calcined powder

Dense BaTi₂O₅ are fabricated from the conventional calcined powder by using spark plasma sintering and by adding MnO₂ as a dopant. The effects of the sintering temperature and the amount of MnO₂ on the phase purity are symmetrically investigated. A pure BaTi₂O₅ phase is obtained under a condition with the sintering temperature of 1,055 °C and the amount of MnO₂ doping of 0.2 wt% from the conventional powder calcined at 950 °C. The relative density of that ceramics is 98 %. The temperature dependence of dielectric property shows the Curie temperature (T _c) of 446 °C with the peak value of 450. Besides, the ceramics polarization of 0.63 μC/cm² and the coercive field of 2.0 kV/cm at room temperature, respectively.     

Effect of sintering temperature and time on microwave dielectric properties of CaNb2O6 ceramics

The microwave dielectric properties of CaNb₂O₆ ceramics were investigated with a view to their application in mobile communication. The CaNb₂O₆ ceramics were prepared by the conventional solid-state method with various sintering temperatures and sintering times. A maximum density of 4.67 g/cm³ was obtained for CaNb₂O₆ ceramic, sintered at 1,400 °C for 4 h. Dielectric constants (ε _r ) of 13.3–18.1 and quality factor (Q × f) of 12,200–50,000 GHz were obtained at sintering temperatures in the range 1,300–1,500 °C for 4 h. Dielectric constants (ε _r ) of 18.0–18.1 and quality factor (Q × f) of 44,300–50,000 GHz were obtained for sintering times in the range 2–6 h at a sintering temperature of 1,400 °C. A dielectric constant (ε _r ) of 18.1, a quality factor (Q × f) of 50,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?54 ppm/°C were obtained when CaNb₂O₆ ceramics were sintered at 1,400 °C for 4 h.     

Low temperature sintering and microwave dielectric properties of MgNb2O6 ceramics

The effects of co-doped CuO and B₂O₃ addition on the sintering temperature, microstructure and microwave dielectric properties of MgNb₂O₆ ceramics prepared with conventional solid-state route were investigated. When both CuO and B₂O₃ were added, the MgNb₂O₆ ceramics were not only sintered at 1000 °C but also improved the Qf value. MgNb₂O₆ ceramics can be well sintered to approach to 98.1% theoretical density with 2.0 wt.% CuO–B₂O₃ additive due to its liquid phase effect. With 2.0 wt.% CuO–B₂O₃, a dielectric constant of 21.5, a Qf value of 108,000(GHz) and a τ _f value of −44 ppm/°C of MgNb₂O₆ ceramics doped with CuO–B₂O₃ sintered at 1050 °C for 2 h are obtained. The variation of ε _r, Qf and τ _f were also explained based on the difference in microstructures.     

Orientation dependence of dielectric and relaxor behaviour in Aurivillius phase BaBi2Nb2O9 ceramics prepared by spark plasma sintering

Grain-oriented Aurivillius phase BaBi₂Nb₂ O₉ ceramics were fabricated using Spark Plasma Sintering (SPS). Their relaxor behaviour was confirmed by a strong frequency dispersion of the dielectric response. The dielectric behaviour has been fitted using different relaxor models. The relaxor parameters are isotropic, while the dielectric constants are highly anisotropic. The piezoelectric constant d ₃₃ is zero perpendicular and parallel to the hot pressing direction, and the P–E response is dominated by losses. The inability to pole the samples at room temperature is consistent with the T _f temperature (∼ ∼115 K) estimated from fitting the experimental data to the Vogel–Fulcher model. This suggests that it may be possible to observe piezoelectric and ferroelectric properties at very low temperatures.     

Phase stability, low temperature cofiring and microwave dielectric properties of BaTi5O11 ceramics with BaCu(B2O5) addition

The effects of BaCu(B₂O₅) (BCB) additions on the sintering temperature, microstructure and microwave dielectric properties of BaTi₅O₁₁ modified with 1.0 wt% CuO (BTC) ceramic have been investigated using X-ray diffraction, scanning electron microscopy and dielectric measurement. The BTC ceramic shows a high sintering temperature (~1,100 °C) and good microwave dielectric properties as Q × f = 44,530 GHz, ε _r = 40.5, τ _f  = 39 ppm/°C. The addition of BCB to BTC effectively reduced the sintering temperature from 1,100 to 925 °C. The reduced sintering temperature was attributed to the BCB liquid phase. The BTC ceramic doped with 4 wt% BCB has a good microwave dielectric properties with Q × f = 25,502 GHz, ε _r = 37.4, τ _f  = 33.1 ppm/°C. The chemical compatibility of silver electrodes and low-fired samples has also been investigated.     

Influence of sintering temperature on secondary phases formation and microwave dielectric properties of Ca2Ce2Ti5O16 ceramics

Ca₂Ce₂Ti₅O₁₆ dielectric ceramics prepared by conventional solid-state ceramic route was investigated. Phase composition and microwave dielectric properties were measured using XRD and Vector network analyzer, respectively. XRD analysis of the calcined and sintered samples revealed the formation of CeO₂ and another unidentified phase (that vanished at ? 1400 °C) as secondary phases along with the parent Ca₂Ce₂Ti₅O₁₆ phase. The amount of the parent Ca₂Ce₂Ti₅O₁₆ phase increased with increasing sintering temperature from 1350 °C to 1450 °C accompanied by a decrease in the apparent density. The density decreased but ? _r and Q _u f _o increased with sintering temperature. An ? _r ～ 81.5, Q _u f _o ～ 5915 GHz and τ _f ～ 219 GHz were achieved for the sample sintered at 1450 °C.     

Effect of V2O5 and CuO additives on sintering behavior and microwave dielectric properties of BiNbO4 ceramics

The influences of V₂O₅ and CuO additives on the sintering behavior and microwave dielectric properties of BiNbO₄ ceramics were investigated. The V₂O₅ and CuO additives lowered the sintering temperature of BiNbO₄ ceramics to the range 875 °C–935 °C. All BiNbO₄ compounds with additives had the orthorhombic structure. The dielectric constant _r was not significantly changed, while the unloaded Q value was affected with additives. The Qf value was found to be a function of the sintering temperatures and the amount of additives. It varied from 4500 to 15800 (GHz) and 1000 to 8000 (GHz) with additives V₂O₅ and CuO, respectively. The _f values were increased in positive values with V₂O₅ doped, while decreased in negative values with CuO addition. V₂O₅ and CuO additives effectively improved the densification and dielectric properties of BiNbO₄ ceramics. The correlation between the microstructure and the Qf value was observed with different additives.     

机械合金化和放电等离子烧结制备Y3Al5O12陶瓷

采用机械合金化和放电等离子烧结制备YAG陶瓷,研究了球磨时间对原料颗粒大小和烧结合成YAG纯度的影响,并利用x射线衍射(XRD)、扫描电镜(SEM)等手段对反应过程及产物形貌和物相进行了分析.研究结果表明,机械合金化Y2O3和Al2O3粉体,可明显细化氧化物颗粒,球磨20h后,Y2O3和Al2O3晶粒大小约为34nm和32nm.球磨处理的Y2O3和Al2O3粉体具有很高的活性,促进放电等离子烧结低温反应合成和获得致密的YAG.对球磨20h的粉体在不同温度进行放电等离子烧结,在1200℃即可获得纯YAG陶瓷,在1500℃烧结,可得到相对密度为99.5%的YAG陶瓷.1500℃烧结的块体在可见光范围内透过率为13.8%.     

Microwave dielectric properties of B2O3 doped LaAlO3 ceramics at low sintering temperature

The microwave dielectric properties and the microstructures of LaAlO₃ ceramics with B₂O₃ additions (0.25–1 wt%) prepared with conventional solid-state route have been investigated. Doping with B₂O₃ (up to 0.5 wt%) can effectively promote the densification of LaAlO₃ ceramics. It is found that LaAlO₃ ceramics can be sintered at 1400°C due to the liquid phase effect of B₂O₃ addition. The Q × f value as well as the dielectric constant decreases at higher B₂O₃ doping level (1 wt%) due to the increase of boundary phases. At 1460°C, LaAlO₃ ceramics with 0.5 wt% B₂O₃ addition possesses a dielectric constant ( _r ) of 22.9, a Q × f value of 44700 (at 9 GHz) and a temperature coefficients of resonant frequency ( _f ) of –36 ppm/°C. The B₂O₃-doped LaAlO₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

Properties of Mn-doped BaTi4O9-ZnO-Ta2O5 ceramics

In Part I, the reaction sequence, microstructural analysis and microwave dielectric properties of manganese-doped BaTi₄O₉ + ZnO + Ta₂O₅ ceramics are discussed. This composition undergoes complex intermediate reactions during calcination. However, the final crystal phases after the sintering process were identical regardless of calcination temperature. Meanwhile, different calcination temperatures affect the relative volume fractions of the BaZn₂Ti₄O₁₁ phase and result in variations in T _f values. To analyse the microstructure, SEM, TEM and EDS analysis were performed. Mn dopants greatly enhanced the Q factor, up to 11000 at 4.5 GHz, whereas undoped ceramics indicated a high loss, probably due to the formation of Ti³⁺ during sintering in air.     

Effect of sintering temperature on optical properties and microstructure of translucent zirconia prepared by high-pressure spark plasma sintering

Abstract

Aiming to characterize the effect of sintering temperature on transparency of zirconia, we have evaluated the optical properties and microstructure of translucent cubic zirconia prepared by high-pressure spark plasma sintering (SPS) at 1000–1200 ^○C. Color centers (oxygen vacancies with trapped electrons) and residual pores were primary defects in the samples. In SPS samples, the total forward transmittance and in-line transmittance are mainly affected by color centers with a limited contribution from residual pores; in contrast, the changes in reflectance are only related to the porosity. The amounts of color centers and residual pores increase with sintering temperature that reduces the total forward and in-line transmittance of the as-sintered zirconia. Annealing in oxidizing atmosphere improves the total forward and in-line transmittance. During the annealing, the concentration of color centers decreases but the porosity increases.     

Effect of sintering temperature on optical properties and microstructure of translucent zirconia prepared by high-pressure spark plasma sintering

Aiming to characterize the effect of sintering temperature on transparency of zirconia, we have evaluated the optical properties and microstructure of translucent cubic zirconia prepared by high-pressure spark plasma sintering (SPS) at 1000–1200 ^○C. Color centers (oxygen vacancies with trapped electrons) and residual pores were primary defects in the samples. In SPS samples, the total forward transmittance and in-line transmittance are mainly affected by color centers with a limited contribution from residual pores; in contrast, the changes in reflectance are only related to the porosity. The amounts of color centers and residual pores increase with sintering temperature that reduces the total forward and in-line transmittance of the as-sintered zirconia. Annealing in oxidizing atmosphere improves the total forward and in-line transmittance. During the annealing, the concentration of color centers decreases but the porosity increases.     

Effect of sintering temperature on microstructures and mechanical properties of spark plasma sintered nanocrystalline aluminum

Organic-coated aluminum nano-powders were consolidated by spark plasma sintering technique with low initial pressure of 1 MPa and high holding pressure of 300 MPa at different sintering temperature. The effect of sintering temperature on microstructures and mechanical properties of the compact bulks was investigated. The results indicate that both the density and the strain of the nanocrystalline aluminum increase with an increase in sintering temperature. However, the micro-hardness, compressive strength and tensile stress of the compact bulks increase initially and then decrease with increasing sintering temperature. The nanocrystalline aluminum sintered at 773 K has the highest micro-hardness of 3.06 GPa, the best compressive strength of 665 MPa and the supreme tensile stress of 282 MPa. A rapid grain growth of nanocrystalline aluminum sintered at 823 K leads to a decrease in micro-hardness, compressive strength and tensile stress. After annealing, a remarkable increase in strain and a slight rise in strength were obtained due to the relief of the residual stress in nanocrystalline Al and the formation of composite structure.     

Low temperature sintering and microwave dielectric properties of zinc silicate ceramics

Effects of ZnO–B₂O₃–SiO₂ glass on the sintering behavior, the microstructure, and the microwave dielectric properties of Zn₂SiO₄ ceramics have been investigated. The ZnO–B₂O₃–SiO₂ glass lowered the sintering temperature of Zn₂SiO₄ ceramics effectively from 1300 to 900 °C. The X-ray diffraction results showed that the secondary phase of SiO₂ in the Zn₂SiO₄ ceramics could be dissolved in the glass. The dielectric constant decreased slightly, and the quality factor decreased with increasing glass content. Especially, when the glass content was chosen as 20 wt%, the ceramics sintered at 900 °C for 2 h exhibited a low dielectric constant of 6.85, a high quality factor of 31,690 and the temperature coefficient of the resonant frequency of −28 ppm/°C, which demonstrated a good potential for use in low temperature co-fired ceramics field.     

四钛酸钡纤维陶瓷的制备及介电性研究

首次制备了BaTi4O9纤维陶瓷新材料。利用XRD分析烧结前后试样的相组分变化并在SEM和TEM下观察分析试样的微观结构。初步研究了材料的介电性能。     

Effects of sintering temperature on the microstructure and dielectric properties of titanium dioxide ceramics

Nanostructured (~200 nm grain size) titanium dioxide (TiO₂) ceramics were densified at temperature as low as 800 °C by pressureless sintering in a pure oxygen atmosphere. Phase transition and microstructural development of sintered samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Dielectric properties including d.c. conductivity, dielectric constant, loss tangent, and dielectric breakdown strength (BDS) were determined for samples sintered at various temperatures. The influence of sintering temperature on the microstructural development, defect chemistry, and dielectric properties of TiO₂ is discussed. Nanostructured TiO₂ ceramics with high sintering density (>98%) lead to improved dielectric properties; high BDS (~1800 kV/cm), low electrical conductivity (~5 × 10⁻¹⁵ S/cm), high dielectric constant (~130), and low loss tangent (~0.09% at 1 kHz), which is promising for application in high energy density capacitors.