Mapping the Mechanical Properties of Hierarchical Supercrystalline Ceramic-Organic Nanocomposites

Little Adjustments Significantly Simplify the Gram-Scale Synthesis of High-Quality Iron Oxide Nanocubes

This work presents a facile one-step protocol for the gram-scale synthesis of iron oxide nanocubes with adjustable sizes ranging from 13 to 20 nm and with size distributions between 7 and 12%. As X-ray diffraction indicated the initial formation of the wüstite phase, a formation mechanism of the nanocubes based on the wüstite crystal structure is proposed. When exposed to ambient conditions, the nanoparticles rapidly oxidize to magnetite/maghemite with a remaining wüstite core. The cubic morphology is attributed to the thermodynamic stability of the exposed {100} facets and the control over the growth rate via the use of a sodium oleate/oleic acid mixed ligand system. In contrast to previously reported procedures, the described synthetic approach does not require the initial preparation and isolation of iron oleate. Therefore, the amount of work and the consumption of hazardous solvents are significantly reduced. Thus, the method presented is much more efficient and environmentally more friendly while maintaining excellent control over the particles' shape, size, and size distribution.

Tunable Microwave Dielectric Properties of Ca0.6La0.8/3TiO3 and Ca0.8Sm0.4/3TiO3-Modified (Mg0.6Zn0.4)0.95Ni0.05TiO3 Ceramics with a Near-Zero Temperature Coefficient

The microstructures and microwave dielectric properties of (Mg_0.6Zn_0.4)_0.95Ni_0.05TiO₃ with Ca_0.6La_0.8/3TiO₃ and Ca_0.8Sm_0.4/3TiO₃ additions prepared by the solid-state method has been investigated. The crystallization and microstructures of these two mixed dielectrics were checked by XRD, EDX, BEI, and SEM to demonstrate two phase systems. Furthermore, the tunable dielectric properties can be achieved by adjusting the amounts of Ca_0.6La_0.8/3TiO₃ and Ca_0.8Sm_0.4/3TiO₃ additions, respectively. After optimization of processed parameters, a new dielectric material system 0.88(Mg_0.6Zn_0.4)_0.95Ni_0.05TiO₃-0.12Ca_0.6La_0.8/3TiO₃ possesses a permittivity (ε_r) of 24.7, a Qf value of 106,000 (GHz), and a τ_f value of 3.8 (ppm/°C), with sintering temperature at 1225 °C for 4 h. This dielectric system with a near-zero temperature coefficient and appropriate microwave properties revealed a high potential for high-quality substrates adopted in wireless communication devices.

Deformation Behavior of Cross-Linked Supercrystalline Nanocomposites: An in Situ SAXS/WAXS Study during Uniaxial Compression

With the ever-expanding functional applications of supercrystalline nanocomposites (a relatively new category of materials consisting of organically functionalized nanoparticles arranged into periodic structures), it becomes necessary to ensure their structural stability and understand their deformation and failure mechanisms. Inducing the cross-linking of the functionalizing organic ligands, for instance, leads to a remarkable enhancement of the nanocomposites' mechanical properties. It is however still unknown how the cross-linked organic phase redistributes applied loads, how the supercrystalline lattice accommodates the imposed deformations, and thus in general what phenomena govern the overall material's mechanical response. This work elucidates these aspects for cross-linked supercrystalline nanocomposites through an in situ small- and wide-angle X-ray scattering study combined with uniaxial pressing. Because of this loading condition, it emerges that the cross-linked ligands effectively carry and distribute loads homogeneously throughout the nanocomposites, while the superlattice deforms via rotation, slip, and local defects generation.

A Study of the Effect of Sintering Conditions of Mg0.95Ni0.05Ti3 on Its Physical and Dielectric Properties

Mg_0.95Ni_0.05TiO₃ ceramics were prepared by traditional solid-state route using sintering temperatures between 1300 and 1425 °C and holding time of 2–8 h. The sintered samples were characterized for their phase composition, micro-crystalline structure, unit–cell constant, and dielectric properties. A two-phase combination region was identified over the entire compositional range. The effect of sintering conditions was analyzed for various properties. Both permittivity (ε_r) and Q factor (Q_f) were sensitive to sintering temperatures and holding times, and the optimum performance was found at 1350 °C withholding time of 4 h. The temperature coefficient of resonant frequency (τ_f) in a range from −45.2 to −52 (ppm/°C) and unit–cell constant were not sensitive to both the sintering temperature and holding time. An optimized Q factor of 192,000 (GHz) related with a permittivity (ε_r) of 17.35 and a temperature coefficient (τ_f) of −47 (ppm/°C) was realized for the specimen sintered at 1350 °C withholding time of 4 h. For applications of 5G communication device (filter, antennas, etc.), Mg_0.95Ni_0.05TiO₃ is considered to be a suitable candidate for substrate materials.