Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) is considered to be one of the promising solid-state electrolytes owing to its excellent chemical and thermal stability, wide potential range (~5.0 V), and high ionic conductivity (~10^-4 S/cm). LATP powders are typically prepared via the sol-gel method by adding and mixing nitrate or alkoxide precursors with chelating agents. Here, the thermal properties, crystallinity, density, particle size, and distribution of LATP powders based on chelating agents (citric acid, acetylacetone, EDTA) are compared to find the optimal conditions for densely sintered LATP with high purity. In addition, the three types of LATP powders are utilized to prepare sintered solid electrolytes and observe the microstructure changes during the sintering process. The pyrolysis onset temperature and crystallization temperature of the powder samples are in the order AC-LATP > CA-LATP > ED-LATP, and the LATP powder utilizing citric acid exhibits the highest purity, as no secondary phase other than LiTi₂PO₄ phase is observed. LATP with citric acid and acetylacetone has a value close to the theoretical density (2.8 g/cm³) after sintering. In comparison, LATP with EDTA has a low sintered density (2.2 g/cm³) because of the generation of many pores after sintering.

Epoxy-based composites find extensive application in electronic packaging due to their excellent processability and insulation properties. However, conventional epoxy-based polymers exhibit limitations in terms of thermal properties and insulation performance. In this study, we develop epoxy-based siloxane/silica composites that enhance the thermal, mechanical, and insulating properties of epoxy resins. This is achieved by employing a sol–gelsynthesized siloxane hybrid and spherical fused silica particles. Herein, we fabricate two types of epoxy-based siloxane/ silica composites with different siloxane molecular structures (branched and linear siloxane networks) and investigate the changes in their properties for different compositions (with or without silica particles) and siloxane structures. The presence of a branched siloxane structure results in hardness and low insulating properties, while a linear siloxane structure yields softness and highly insulating properties. Both types of epoxy-based siloxane/silica composites exhibit high thermal stability and low thermal expansion. These properties are considerably improved by incorporating silica particles. We expect that our developed epoxy-based composites to hold significant potential as advanced electronic packaging materials, offering high-performance and robustness.

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• Enhanced Epoxy Composites Reinforced by 3D-Aligned Aluminum Borate Nanowhiskers
  Hyunseung Song, Kiho Song, Haejin Hwang, Changui Ahn
  Materials.2024; 17(19): 4727.     CrossRef

Li_1.3Al_0.3Ti_1.7(PO₄)₃(LATP) is considered a promising material for all-solid-state lithium batteries owing to its high moisture stability, wide potential window (~6 V), and relatively high ion conductivity (10^-3–10^-4 S/cm). Solid electrolytes based on LATP are manufactured via sintering, using LATP powder as the starting material. The properties of the starting materials depend on the synthesis conditions, which affect the microstructure and ionic conductivity of the solid electrolytes. In this study, we synthesize the LATP powder using sol-gel and co-precipitation methods and characterize the physical properties of powder, such as size, shape, and crystallinity. In addition, we have prepared a disc-shaped LATP solid electrolyte using LATP powder as the starting material. In addition, X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopic measurements are conducted to analyze the grain size, microstructures, and ion conduction properties. These results indicate that the synthesis conditions of the powder are a crucial factor in creating microstructures and affecting the conduction properties of lithium ions in solid electrolytes.

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• Controlling the All-Solid Surface Reaction Between an Li1.3Al0.3Ti1.7(PO4)3 Electrolyte and Anode Through the Insertion of Ag and Al2O3 Nano-Interfacial Layers
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Cost-effective functional phosphor nanoparticles are prepared by introducing low-cost SiO₂ spheres to rareearth phosphor (YVO₄:Eu³⁺, YVO₄:Er³⁺, and YVO₄:Nd³⁺) shells using a sol-gel synthetic method. These functional nanoparticles are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and general photoluminescence spectra. The SiO₂ sphere occupying the interior of the conventional phosphor is advantageous in significantly reducing the cost of expensive rare-earth phosphor nanoparticles. The sol-gel process facilitates the core–shell structure formation; the rare-earth shell phosphor has strong interactions with chelating agents on the surfaces of SiO₂ nanoparticles and thus forms layers of several nanometers in thickness. The photoluminescence wavelength is simply tuned by replacing the active materials of Eu³⁺, Er³⁺, and Nd³⁺. Moreover, the photoluminescent properties of the core–shell nanoparticles can be optimized by manipulating the specific contents of active materials in the phosphors. Our simple approach substitutes low-cost SiO₂ for expensive rare-earth-based phosphor materials to realize cost-effective phosphor nanoparticles for various applications.

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• Enhanced Energy-Transfer Properties in Core-Shell Photoluminescent Nanoparticles Using Mesoporous SiO₂ Intermediate Layers
  Woo Hyeong Sim, Seyun Kim, Weon Ho Shin, Hyung Mo Jeong
  Korean Journal of Metals and Materials.2020; 58(2): 137.     CrossRef

The sol-gel method is the simplest method for synthesizing monodispersed silica particles. The purpose of this study is to synthesize uniform, monodisperse spherical silica nanoparticles using tetraethylorthosilicate (TEOS) as the silica precursor, ethanol, and deionized water in the presence of ammonia as a catalyst. The reaction time and temperature and the concentration of the reactants are controlled to investigate the effect of the reaction parameters on the size of the synthesized particles. The size and morphology of the obtained silica particles are investigated using transmission electron microscopy and particle size analysis. The results show that monodispersed silica particles over a size range of 54-504 nm are successfully synthesized by the sol-gel method without using any additional process. The nanosized silica particles can be synthesized at higher TEOS/H2O ratios, lower ammonia concentrations, and especially, higher reaction temperatures.

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• Nanostructure Construction of SiO₂@Au Core-Shell by In-situ Synthesis
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10 wt.% and 20 wt.%Li-TiO₂ composite powders are synthesized by a sol-gel method using titanium isopropoxide and Li₂CO₃ as precursors. The as-received amorphous 10 wt.%Li-TiO₂ composite powders crystallize into the anatase-type crystal structure upon calcination at 450°C, which then changes to the rutile phase at 750°C. The asreceived 20 wt%Li-TiO₂ composite powders, on the other hand, crystallize into the anatase-type structure. As the calcination temperature increases, the anatase TiO₂ phase gets transformed to the LiTiO₂ phase. The peaks for the samples obtained after calcination at 900°C mainly exhibit the LiTiO₂ and Li₂TiO₃ phases. For a comparison of the photocatalytic activity, 10 wt.% and 20 wt.% Li-TiO₂ composite powders calcined at 450°C, 600°C, and 750°C are used. The 20 wt.%Li-TiO₂ composite powders calcined at 600°C show excellent efficiency for the removal of methylorange.

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  journal of Korean Powder Metallurgy Institute.2018; 25(3): 257.     CrossRef
• Synthesis and characterization of nitrogen-doped TiO 2 coatings on reduced graphene oxide for enhancing the visible light photocatalytic activity
  Yifan Zhang, Hye Mee Yang, Soo-Jin Park
  Current Applied Physics.2018; 18(2): 163.     CrossRef

Tungsten trioxide thin films are successfully synthesized by a sol-gel method using tungsten hexachloride as precursors. The structural, chemical, and optical properties of the prepared films are characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-Vis spectrophotometry. The electrochemical and electrochromic properties of the films before and after heat treatment are also investigated by cyclic voltammetry, chronoamperometry, and in situ transmittance measurement system. Compared to as-prepared films, heattreated tungsten trioxide thin films exhibit a higher electrochemical reversibility of 0.81 and superior coloration efficiency of 65.7 cm²/C, which implies that heat treatment at an appropriate temperature is a crucial process in a sol-gel method for having a better electrochromic performance.