Vapor Growth and Chemical Delithiation of Stoichiometric LiCoO₂ Crystals

Single crystals of LiCoO₂ have been grown by a vapor transport method at high temperature and normal atmospheric pressure. The plate-like single crystals have large (00<i>l</i>) facets (up to 1 mm²) and thicknesses ranging from 5 to 50 μm. A single-crystal X-ray diffraction study confirmed the trigonal <i>R</i>3̅<i>m</i> space group with lattice parameters <i>a</i> = 2.8150(3) Å and <i>c</i> = 14.0516(6) Å at room temperature. Electrical transport measurements indicated that as-grown crystals are highly insulating, with electrical resistivity in the order of TΩ cm at room temperature. This contrasts with the value of 5 Ω cm previously reported for a flux-grown crystal and suggests that vapor growth crystals may have fewer defects. Li-ion deintercalation of LiCoO₂ crystals was carried out by a chemical extraction process. A quasi-in situ XRD approach was utilized to monitor the structural evolution during the Li-ion extraction process, which exhibited the progression of phases widely established for this system, but also shows evidence of inhomogeneous delithiation mechanism. Transport measurements confirm metallic behavior for delithiated Li_<i>x</i>CoO₂ crystals (0.5 < <i>x</i> < 1.0) with anomalies in the temperature of 150–180 K

Investigation of Phase Transition and Ultrawide Band Gap Engineering in MgGaO Semiconductor Thin Films

Magnesium gallium oxide (MgGaO) ternary alloys with band gap energy larger than ∼5.0 eV can provide opportunities for optoelectronics in the deep ultraviolet spectral range and power electronics with extremely high critical field strength. It is important to grow high-quality MgGaO alloys with varied Mg compositions and understand their structural and optical properties. From this perspective, 20 MgGaO samples with Mg atomic percentages from 0 to 100% were grown by using oxygen plasma-assisted molecular beam epitaxy. Band gap tuning from 5.03 to 5.89 eV was achieved for the ternary alloys, and all samples had a transmittance of over ∼90% in the visible spectral range. The lattice structures were confirmed to transform from the β phase in Ga-rich materials to the β and rocksalt mixture phase in high-Ga high-Mg alloys and to the pure rocksalt phase in Mg-rich alloys. How lattice parameters change with the increase of Mg atom % and the epitaxy relationship between MgGaO films and c-sapphire substrates were revealed

Direct Synthesis of Bimetallic Pd₃Ag Nanoalloys from Bulk Pd₃Ag Alloy

We report a transformative, all inorganic synthesis method of preparing supported bimetallic Pd₃Ag alloy nanoparticles. The method involves breaking down bulk Pd₃Ag alloy into the nanoparticles in liquid lithium, converting metallic Li to LiOH, and transferring Pd₃Ag nanoparticles/LiOH mixture onto non-water-soluble supports, followed by leaching off the LiOH with water under ambient conditions. The size of the resulting Pd₃Ag nanoparticles was found narrowly distributed around 2.3 nm characterized by transmission electron microscope (TEM). In addition, studies by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy, and X-ray absorption near edge structure (XANES) spectroscopy showed that the resulting Pd₃Ag nanoparticles inherited similar atomic ratio and alloy structure as the starting material. The synthesized Pd₃Ag nanoparticles exhibited excellent catalytic activity toward hydrogenation of acrolein to propanal