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Homogeneous, nanocrystalline La1-xSrxMnO3 (LSM) powders, with x ∼ 0.15, were synthesized with the epoxide addition sol−gel method. Through this simple technique, sol−gel materials were prepared from methanolic solutions of metal chlorides without the need for alkoxides, polymeric gel agents, or elaborate reaction schemes. The gels were dried in ambient conditions, resulting in mesoporous xerogels with networked nanostructures interconnecting particulate regions. Calcination of the dried gels resulted in the crystallization of single-phase LSM by 700 °C, after decomposition of intermediate hydroxide, chloride, and oxychloride compounds. SEM analysis indicated that the calcined powders were nanocrystalline and consisted of discrete particles, free of hard agglomeration. The average crystallite size and equivalent spherical diameter determined from XRD line broadening and BET analysis, respectively, were in good agreement with the SEM results (∼100 nm). The activation energies for the electronic conductivity...

Various reaction conditions, such as reductant, time, procedure, concentration, and temperature, were investigated with the aim of finding a simple, optimized synthetic route for the synthesis of crystalline germanium nanoparticles. Results from these studies indicate that sodium naphthalide is an ideal reductant and that the reaction is virtually complete within 10 min. Furthermore, it was observed that a two-pot synthesis resulted in a cleaner, narrower distribution of nanoparticle size and that the narrowest size distribution (∼20%) was produced when a dilute Na(naphth) in glyme mixture was utilized. The optimum initial reduction temperature was found to be 0 °C. It was also shown that concentration and temperature play an important role in controlling nanoparticle size. The best reaction conditions, as stated above, produced nanoparticles with a size dispersion of ∼20% when combined. Transmission electron microscopy (TEM), selected-area electron diffraction (SAED), high-resolution TEM (HRTEM), energy-...

Butyl-capped crystalline germanium (Ge) nanoparticles were synthesized at room temperature in dimethoxyethane by reduction of GeCl4 with Na(naphthalide) and subsequent reaction with butyl Grignard. The nanoparticles were isolated in hexane and characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), elemental analysis, and X-ray powder diffraction (XRD). The product from this room-temperature reaction was heated under vacuum at temperatures of 200−600 °C at 50 °C intervals. The product obtained from the 300 °C treatment was soluble in hexane, while the products from temperatures greater than 300 °C were not. SAED was consistent with crystalline Ge from the initial synthesis at room temperature and amorphous Ge for the product heated under vacuum to 300 °C. X-ray powder diffraction of the 300 °C product shows the transition from amorphous to crystalline nanoparticles occurring between 550 and 600 °C. TEM shows that the n...

Homogeneous, nanocrystalline powders of yttria-stabilized zirconia (YSZ) were prepared using a non-alkoxide sol−gel method. Monolithic gels, free of precipitation, were prepared by addition of propylene oxide to aqueous solutions of Zr4+ and Y3+ chlorides at room temperature. The gels were dried with supercritical CO2(l), resulting in amorphous aerogels that crystallized into stabilized ZrO2 following calcination at 500 °C. The aerogels and resulting crystalline products were characterized using in situ temperature profile X-ray diffraction, Raman spectroscopy, thermal analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen adsorption/desorption analysis, and elemental analysis by inductively coupled plasma-atomic emission spectroscopy. TEM and N2 adsorption/desorption analysis of an aerogel prepared by this method indicated a porous network structure with a high surface area (409 m2/g). The crystallized YSZ maintained high surface area (159 m2/g) upon formation of h...

The effect of Y 2 O 3 -stabilized ZrO 2 (YSZ) particle size on composite YSZ -(La 0 . 8 5 Sr 0 . 1 5 ) 0 . 9 8 MnO 3 (LSM) cathode microstructure and performance was examined. Two nanocrystalline YSZ powders were compared withdifferent particle size and surface areas; a commercial powder with ∼100 nm particles and 11 m 2 /g surface area and a synthesized YSZ powder with ∼10 nm particles and 124 m 2 /g surface area. The LSM phase of the composite was the same in both systems. Anode supported single cells were fabricated and the electrochemical performances measured. The cathode microstructures for the high surface area YSZ composites were examined as a function of sintering temperature and compared to the lower surface area YSZ composite cathode sintered at 1150 °C. The larger surface area YSZ was prepared using a novel epoxide initiated sol-gel synthesis, followed by aerogel processing. The aerogels were characterized with TEM, SEM, BET surface area analysis, and powder XRD.

Homogeneous, nanocrystalline La1-xSrxMnO3 (LSM) powders, with x ∼ 0.15, were synthesized with the epoxide addition sol−gel method. Through this simple technique, sol−gel materials were prepared from methanolic solutions of metal chlorides without the need for alkoxides, polymeric gel agents, or elaborate reaction schemes. The gels were dried in ambient conditions, resulting in mesoporous xerogels with networked nanostructures interconnecting particulate regions. Calcination of the dried gels resulted in the crystallization of single-phase LSM by 700 °C, after decomposition of intermediate hydroxide, chloride, and oxychloride compounds. SEM analysis indicated that the calcined powders were nanocrystalline and consisted of discrete particles, free of hard agglomeration. The average crystallite size and equivalent spherical diameter determined from XRD line broadening and BET analysis, respectively, were in good agreement with the SEM results (∼100 nm). The activation energies for the electronic conductivity...

In situ high-resolution transmission electron microscopy (HRTEM) was used to investigate the effect of heating on an organo-Ge polymer/nanoparticle composite material containing 4-8 nm diameter alkyl-terminated Ge nanoparticles. The product was obtained from the reduction of GeCl4 with Na(naphthalide) with subsequent capping of the -Cl surface with n-butyl Grignard reagent. The in situ HRTEM micrographs show that the product undergoes significant changes upon heating from room temperature to 600 degrees C. Two pronounced effects were observed: (i) Ge nanoparticles coalesce and remain crystalline throughout the entire temperature range, and (ii) the organo-Ge polymer acts as a source for the in situ formation of additional Ge nanoparticles. The in situ-formed Ge nanoparticles are approximately 2-3 nm in diameter. These in situ-formed nanoparticles (2-3 nm) are so dense that, together with the original ones, they build up an almost continuous crystalline film in the temperatures between 300 and 500 degrees C. Above 480 degrees C, melting of the in situ formed Ge nanoparticles (2-3 nm) is observed, while nanoparticles greater than 5 nm remain crystalline. After cooling to room temperature, the 2-3 nm Ge nanoparticles recrystallized.