Structural, thermodynamic and electronic aspects of the lambda transformation in graphite nitrates

✍ Scribed by A.R. Ubbelohde

• Publisher: Elsevier Science
• Year: 1968
• Tongue: English
• Weight: 587 KB
• Volume: 6
• Category: Article
• ISSN: 0008-6223
• DOI: 10.1016/0008-6223(68)90301-1

✦ Synopsis

Graphite nitrates of several sequences have been prepared by vapour phase nitration. Properties measured over a wide range of temperatures include thermal expansions, X-ray diffractions, electrical resistivities and thermoelectric power (TEP). The good metallic conduction and strongly positive TEP of these nitrates points to structures with carbon hexagon networks as macro-cations. Nitrate anions and nitric acid molecules are intercalated to an approximate formula C,,+NO,-JHNO, for the first sequence. On cooling several of these compounds pass through a lambda type transformation at around -21°C. From X-ray data, the intercalated layers pass from liquid like disorder to crystalline order over a range of temperatures. Electrical resistivities decrease with falling temperatures more steeply in the lambda region where there is marked hysteresis, as is characteristic of lambda transformations generally. A peak value of TEP is observed in the lambda region; this novel effect is attributed to scattering of charge carriers by domains in "hybrid" crystal structures formed in this region.