ABSTRACT
We report the synthesis of the Delafossite honeycomb compounds Cu3Ni2SbO6 and Cu3Co2SbO6 via a copper topotactic reaction from the layered α-NaFeO2-like precursors Na3Ni2SbO6 and Na3Co2SbO6. The low-temperature exchange reaction exclusively produces the rhombahedral 3R polytype subcell, whereas only the hexagonal 2H polytype subcell has been made by conventional synthesis. The thus-synthesized 3R variants are visually striking; they are bright lime-green (Ni variant) and terracotta-orange (Co variant), while both of the conventionally synthesized 2H variants have a burnt-red color. The new structures are characterized by powder X-ray diffraction and Rietveld analysis as well as magnetic susceptibility, X-ray photoelectron spectroscopy (XPS), and diffuse-reflectance optical spectroscopy. Using thermogravimetric analysis, we identify a second order 3R â 2H phase transition as well as a first-order structural transition associated with rearrangement of the honeycomb stacking layers. The optical absorbance spectra of the samples show discrete edges that correlate well to their visual colors. Exposing Cu3Ni2SbO6 to O2 and heat causes the sample to change color. XPS confirms the presence of Cu(2+) in these samples, which implies that the difference in color between the polytypes is due to oxygen intercalation resulting from their different synthetic routes.
ABSTRACT
The siloxane film derived from the 30-carbon chain triacontyltrichlorosilane (TCTS) is studied as an anti-relaxation coating for atomic vapor cells. The longitudinal spin relaxation lifetime of optically pumped potassium atoms in the presence of TCTS is measured and the average number of non-relaxing atom-wall collisions, or bounces, enabled by the coated surface is determined. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) of TCTS were performed to investigate changes in chemical states and surface morphology of TCTS arising from K atom deposition on the film surface. TCTS was found to give approximately 530 bounces. Following lifetime measurements, K2p signals were clearly observed in XPS spectra. AFM images display non-preferential K deposition on the TCTS surface, however additional AFM studies with a TCTS surface exposed to Rb atoms show deposition occurs along surface defects. In agreement, Rb is found to preferentially deposit along the step edges of an 18-carbon chain monolayer film derived from 1-Octadecene. Finally, AFM indicates a much smoother surface for a tetracontane coating relative to TCTS. The importance of siloxane surface morphology versus film thickness with respect to coating performance is discussed.
