Fan Fang,Haochen Liu,Zuoliang Wen,Chenxi Liu,Bing Xu,Zhikuan Zhang,Kai Wang,Mehmet Ertugrul,Wei Lei,Xiao Wei Sun
Colloidal quantum dots (QDs) are promising luminescent materials for display and lighting, but their stability has long been an issue. Here, we designed a passivation strategy of doping Ti ions into the shell of alloyed CdZnSeS@ZnS QDs. The results showed that Ti ions were successfully doped into the ZnS shell and the stability of QDs was improved. In the aging test, the Ti ions doped QDs maintained 51.4% of the initial performance after 90 h of aging, while the pristine QDs decreased to less than 25% of the initial value. In addition, we discuss the reasons why Ti ions doping improves the stability of QDs. Ti ions are found to form Ti–S bonds in the ZnS shell, which has high binding energy and strong oxidation resistance. Most importantly, since there is no external physical insulating coating, the optimized QDs can also be directly used in electroluminescent devices, showing great potential in electroluminescence applications.
Co-doped TiO 2 ceramics exhibit great potential as high-performance giant dielectric materials. However, their excessively high sintering temperature renders them unsuitable for economical industrial production. The giant permittivity of these ceramics is closely correlated with the concentration of Ti 3+ ions present. Adding a sintering aid to the ceramics is an effective method to reduce the sintering temperature. CuO, a common sintering aid, not only reduces the sintering temperature but also potentially enhances the Ti 3+ ions concentration through the multivalence of Cu element, further optimizing their giant dielectric properties. Therefore, the effects of CuO addition on the sintering condition, microstructure, and dielectric properties of In and Nb co-doped TiO 2 ceramics were investigated. The results indicate that CuO effectively lowers the sintering temperature of the ceramics. However, the presence of a large number of Cu + ions inhibits the formation of Ti 3+ ions, resulting in the disappearance of their giant dielectric properties. Upon annealing at 1150 °C for 2 h in air, the Ti 3+ ions concentration significantly increases in the ceramics, consequently restoring their giant dielectric properties. Additionally, a new dielectric relaxation appears around 100 kHz, likely arising from the conductivity difference between the shallow layers and cores of grains induced by annealing. Furthermore, annealing enhances the grain boundary resistance, thereby reducing the low-frequency dielectric loss of the ceramics.
A novel Ca x Y 3−x Al 5−x Ti x O 12 (0 ≤ x ≤ 2.0) solid solution with garnet structure was synthesized by solid-state reaction technique. Ca 2+ and Ti 4+ substituted for Y 3+ and Al 3+ , respectively. Ca 2+ /Ti 4+ doping reduced the sintering temperature of Ca x Y 3−x Al 5−x Ti x O 12 ceramics to 1450 °C, and it also improved corresponding densification process. Meanwhile, the doping strongly influenced microwave dielectric properties. For the samples sintered at 1550 °C for 3 h, the dielectric constant (ε r ) increased from 7.2 to 34.7 by increasing Ca 2+ /Ti 4+ content, and at the same time the quality factor (Q × f) values increased from 12,000 to 45,200 GHz and then slightly declined to 41,000 GHz. The temperature coefficient of resonant frequency (τ f ) values of these samples increased monotonically from − 40 to + 31 ppm/°C by increasing Ca 2+ /Ti 4+ content. Therefore, Ca x Y 3−x Al 5−x Ti x O 12 solid solution ceramics with x = 1.5 sintered at 1550 °C for 3 h showed optimum microwave dielectric properties: ε r = 32.6, Q × f = 45,200 GHz and τ f = + 7 ppm/°C. Ca x Y 3−x Al 5−x Ti x O 12 (0 ≤ x ≤ 2.0) solid solution ceramics with garnet structure were new promising aluminate ceramics for microwave dielectric application.
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