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Nonstoichiometric TiO2-x compacts were obtained via spark plasma sintering of titanium dioxide powder. The thermoelectric properties of the resulting materials were examined at temperatures varying from 297 to 973 K. Nonstoichiometric TiO2-x compacts were formed and controlled by varying the sintering temperature during the spark plasma sintering process. The as-prepared compacts possessed oxygen deficiencies and various Magnéli phases TinO2n-1 (n = 4–9), because of the complex interplay between the sintering temperature and stoichiometry. The results demonstrated that the introduction of more and more oxygen deficiencies and the resultant formation of Ti4O7 positively affected the electrical resistivity, but also diminished the Seebeck coefficient. Additionally, an increase in the sintering temperature led to a higher reduction degree, causing a further increase in the number of oxygen deficiencies and enhancement of phase evolution and thermal conductivity. Consequently, the introduction of a moderate number of oxygen deficiencies is advisable in upgrading the thermoelectric properties of TiO2. The compact obtained at a sintering temperature of 1073 K displayed a reasonable thermoelectric efficiency (ZT) of 0.169 at 773 K. Furthermore, first-principles calculations demonstrated that the TiO2 band gap is narrowed by the introduction of oxygen deficiencies, and the electrons near the oxygen vacancy can easily break away from atoms, thus leading to the associated electron transition responsible for the significant decrease in electrical resistivity. [ABSTRACT FROM AUTHOR]

P2-type Na2/3Co0.25Mn0.705Si0.045O2 (Si-NCM) high-rate cathode was designed by using silicon of the nonmetallic element as dopant and developed by the simple solid-state route for sodium-ion batteries. XRD refinements confirm the P2-type hexagonal structure with space group (SG: P63/mmc), in which Si4+ ions substitute the Mn site of P2-Na2/3Co0.25Mn0.75O2 (NCM) lattice without any impurity phases of Si-related substances. Si-NCM delivers the initial capacity of 144 mAh g−1 at 0.1 C with the capacity retention of 80.1% after 100 cycles, and the discharge capacity of 120 mAh g−1 at 1 C with 83.4% retention at 200th cycle. Particularly, excellent capacity retentions of 90.2% after 260 cycles and 85.8% after 500 cycles at 5 C have been achieved. Si-doping can expedite the superior cycle stability of Si-NCM compared to NCM, which is attributed to the more powerful Si–O, TM–O and O–O bonds, more stable occupancy rate in the Nae site of unit cell and particularly ascribed to the reversible two-phase transition of P2–P3–P2 in the process of Na+ extraction and intercalation. Hence, SiO2 as dopant is a novel strategy with regard to the development of high-rate cathode materials for SIBs. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNCs) possessing chiral nematic structures have been developed as liquid crystal templates for optical materials and devices. These templates provide materials with advanced structural and optical properties, leading to numerous promising discoveries of new functional materials. In this work, the chiral nematic CNC/silver nanoparticles (CNC/AgNPs) composite membranes were prepared and displayed striking iridescent colors. The addition of AgNPs strengthened the chiral structure of CNC-based composites by adjusting the pitch of the chiral nematic structure. As the AgNPs content decreased from 8 to 2 wt%, a redshift of the reflection wavelength was observed from 475 to 773 nm, and the distance between the two adjacent layers of the membrane increased from 155 to 254 nm, according to a fitted linear function. Therefore, this composite membrane exhibited excellent chiral optical properties, and the chiral reflectance could be tuned accurately by regulating the content ratio of CNCs to AgNPs. New insights into designing advanced functional optics were provided, herein to show their potential applications, such as in smart windows and anti-counterfeit labels. [ABSTRACT FROM AUTHOR]

The foaming behavior of a diglycidyl ether of bisphenol-A (DGEBA) epoxy resin-anhydride hardener system at varying accelerator (tertiary amine) concentration, using chemical foaming agent (CFA), was investigated. The microstructure of foams revealed a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher curing rate by varying accelerator contents, whereas not the same by varying foaming temperatures. The curing of epoxy system was studied by a differential scanning calorimetry, while the decomposition process of CFA was investigated by the foaming pressure measurement. Kinetics data showed that the addition of CFA in epoxy system produced obvious influence on the curing process of epoxy mixture; meanwhile, the decomposition reaction of CFA in epoxy system showed an autocatalytic behavior, which can be well predicted by Šesták-Berggren equation. Reaction rate constants of the curing of epoxy foaming system ( k ) and the degradation of CFA ( k ) were calculated, and the competition between these two simultaneously occurring reactions was expressed by the kinetic parameter k / k . The high specific value of k / k , which can be tuned by both accelerator concentration and foaming temperature, indicated that the curing rate was much higher than degradation rate of CFA. By further accelerating the curing rate in the foaming stage, a new two-step method was introduced to fabricate microcellular epoxy foam at relatively low viscosity. [ABSTRACT FROM AUTHOR]