Effect of cerium doping on optical and scintillation properties of transparent YAG ceramic

Cerium doped transparent YAG ceramics 0.15–2 at% cerium) were prepared using nano-powder technique and vacuum sintering. The effective solubility limit of cerium in YAG was found to lie between 1.0 and 1.5 at%. The PL intensity increases with the cerium content and attains a maximum for 1.0 at% doping. Lifetime of PL is not very sensitive to cerium content, however, a slight decrease in the life-time from 66 ns to 55 ns was observed with increase in cerium content from 0.15 to 2.0 at%. This decrease in PL intensity and life-time is attributed to concentration quenching for the YAG ceramics with cerium content higher than 1.0 at%. A red-shift in the PL peak position was observed and attributed to the local symmetry distortion in YAG matrix.     

Nanostructured insulators – A review of nanotechnology concepts for outdoor ceramic insulators

Nanotechnology is rapidly growing as a new technology alternative to create advance materials with unique characteristics and performance for different applications in several industrial sectors. In recent years, many nanotechnology-based products have appeared in our everyday life. On the other hand, industries have also considered nano-concepts to produce high-added value products with superior capacity, reliability and efficiency. Electric insulators are components with high importance in the electricity network system; reliability and high performance are essential characteristics demanded by actual markets. Recent studies have demonstrated the technical feasibility of innovative nano-concepts to improve the final properties of these electrical components. This paper reviews the state-of-the-art of nanotechnology applications for outdoor insulators. Nano-concepts for ceramic insulators are summarized and reported with the aim to provide an overview of applications and opportunities for electric industry. In addition, the future trends and challenges for this field are also considered in this work.     

Voronoi cell finite element modelling of the intergranular fracture mechanism in polycrystalline alumina

The mechanisms of fracture in polycrystalline alumina were investigated at the grain level using both the micromechanical tests and finite element (FE) model. First, the bending experiments were performed on the alumina microcantilever beams with a controlled displacement rate of 10 nm s^–1 at the free end; it was observed that the intergranular fracture dominates the failure process. The full scale 3D Voronoi cell FE model of the microcantilever bending tests was then developed and experimentally validated to provide the insight into the cracking mechanisms in the intergranular fracture. It was found that the crystalline morphology and orientation of grains have a significant impact on the localised stress in polycrystalline alumina. The interaction of adjacent grains as well as their different orientations determines the localised tensile and shear stress state in grain boundaries. In the intergranular fracture process, the crack formation and propagation are predominantly governed by tensile opening (mode I) and shear sliding (mode II) along grain boundaries. Additionally, the parametric FE predictions reveal that the bulk failure load of the alumina microcantilever increases with the cohesive strength and total fracture energy of grain boundaries.     

High temperature dielectrics in the ceramic system K0.5Bi0.5TiO3-Ba(Zr0.2Ti0.8)O3-Bi(Zn2/3Nb1/3)O3

Ceramics in the system (1-x)[0.5K_0.5Bi_0.5TiO₃-0.5Ba(Zr_0.2Ti_0.8)O₃]-xBi(Zn_2/3Nb_1/3)O₃ have been fabricated by a solid-state processing route for compositions x≤0.3. The materials are relaxor dielectrics. The temperature of maximum relative permittivity, T_m, decreased from 150 °C for composition x=0, to 70 °C for x=0.2. The x=0.2 sample displayed a wide temperature range of stable relative permittivity, ε_r, such that ε_r=805±15% from −20 to 600 °C (1 kHz). Dielectric loss tangent was ≤0.02 from 50 °C to 450 °C (1 kHz), but due to the tanδ dispersion peak, the value increased to 0.09 as temperatures fell from 50 °C to −20 °C. Values of dc resistivity were of the order of ~10⁹ Ω m at 300 °C. These properties are promising in the context of developing new high temperature capacitor materials.     

Bulk boron carbide nanostructured ceramics by reactive spark plasma sintering

Bulk boron carbide (B₄C) ceramics was fabricated from a boron and carbon mixture by use of one-step reactive spark plasma sintering (RSPS). It was also demonstrated that preliminary high-energy ball milling (HEBM) of the B+C powder mixture leads to the formation of B/C composite particles with enhanced reactivity. Using these reactive composites in RSPS permits tuning of synthesized B₄C ceramic microstructure. Optimization of HEBM + RSPS conditions allows rapid (less than 30 min of SPS) fabrication of B₄C ceramics with porosity less than 2%, hardness of ~35 GPa and fracture toughness of ~ 4.5 MPa m ^1/2     

Stability domains of (Ti,W)C and (Ti,W)(CN) during carbothermal reduction of TiO 2/WO3 mixture at 1500 K

Phase stability diagrams for the carbothermal reduction of a mixture of TiO₂ and WO₃ at 1500 K were constructed as a function of the carbon activity, oxygen pressure and characteristics of solution formation. Through this, it was found that the stable domains of carbides/carbonitrides, including (Ti,W)C/(Ti,W)(CN), are larger than the phases that are formed when solid-solution phases are not considered due to their greater stability. The use of a nitrogen atmosphere instead of vacuum expanded the stable domains of the solid-solution phases, indicating that they are made more stable under these conditions. Using these stability diagrams, the reaction sequence of carbothermal reduction can be predicted, and so this study can provide a guideline for preparing tougher carbide/carbonitride (Ti,W)C/(Ti,W)(CN) phases from TiO₂/WO₃ mixtures.     

From bulk to cellular structures: A review on ceramic/graphene filler composites

A revision on ceramic/graphene composites is presented. The more representative results for a wide number of bulk composites are compared, making special emphasis on their mechanical (fracture toughness, strength) and elastic properties, along with wear and friction topics. The electrical functionality boosted by the contacted graphene network is critically assessed for conducting and dielectric ceramic matrices. Regarding thermal transport, the enhancement or depletion of thermal conductivity is reviewed for different materials and specific orientations. Furthermore, new developments on layered materials and coatings, as well as on three-dimensional cellular composites, which certainly widen the scope of applications for this remarkable group of ceramic materials, are looked over.     

陶瓷材料与结构增材制造技术研究现状

增材制造技术在聚合物材料与结构、金属材料与结构制备中已经得到了大量应用。近年来,陶瓷材料与结构的增材制造技术得到了初步发展,受到了越来越多陶瓷工作者的关注。本文综述了目前几种常见的陶瓷材料与结构增材制造技术,并预测了未来陶瓷材料与结构增材制造技术发展的主要关注点,以期为陶瓷工作者提供关于增材制造技术一定的参考与思考。     

Correlating phase and microstructure development versus dielectric properties in La and Er co-doped Bi4Ti3O12 ferroelectric ceramics

Bi_3.25La_0.75−xEr_xTi₃O₁₂ and Bi_3.25La_0.75Ti_3−xEr_xO_12−δ ceramics were prepared and studied in this work in terms of dopant-induced phase and microstructure development as well as dielectric response. The results show that introduction of Er³⁺ tends to reduce the materials’ sintering temperature and average grain size. Moreover, it was noted that in these systems the substitution site of this dopant is controlled by valence state and ionic radii mismatch effects. In particular, even when a nominal substitution of Ti⁴⁺ is conceived, here it is found that Er³⁺ also incorporates at the (Bi,La)³⁺ sites. These and other interesting concluding remarks from this work, including Er³⁺ tolerance, were possible only after comparing, especially, the X-ray diffraction results and the intrinsic ferroelectric characteristics extracted from the dielectric measurements.