A~t~ct-Therms expansion, specific heat and magnetic properties of the "residue" compounds of graphitenitrate were measured at low temperatures between 1.5 and 3OOK. Met&c behaviour of the compound is confirmed from high density of state at Fermi level which was evaluated from specific heat data and from magnetic susceptibility measurements. The effective modulation of structural parameters and of properties with doping of nitrate ions is shown. Phase transitions of the compound are found to occur at cu. 320 and 230 K.
The so-called residue compounds of graphite [ 11 have been studied only by a few investigators. One of the authors has found a special compound of graphite-nitrate[2], which was prepared by the decomposition of the lamellar compound. Its X-ray powder pattern is similar to that of graphite, except for the exact position of diffraction lines and the existence of extra peaks. By calculation of the apparent interlayer spacing (T, from the peaks corresponding to 001 lines of graphite, a smaller value than that for graphite was obtained (down to 3.31A). Five extra peaks with small intensities were found at the diffraction angles lower than the diffraction corresponding to 002 line and their d-spacings to be interrelated with each other and with the apparent interlayer spacing smaller than graphitic. Their metallic behaviour in electronic properties has been reportedl31; iow resistivity along the layer planes (ea. 2 x 10-'&I cm), a very small and negative Hall coefficient which is field inde~ndent and a negligibly small magnetoresistance at liquid nitrogen temperature. Possible explanation of the structure and electronic properties of the compound has been discussed [3].
In the present work, thermal expansion, specific heat, diamagnetic susceptibility, electron spin resonance and magnetic anisotropy were measured at temperatures between 1.5 and 300K on these special residue compounds of ~aphite-ni~ate. Prelimin~y investigations of phase transition of this compound were also carried out.
2 EXpF,RlMENTAL
The "residue" compounds of graphite-nitrate were prepared from the powder of Madagascar natural graphite and from stress-annealed pyrolytic graphite PGCCLJ The original graphites were kept in 96% concentrated nitric acid at room temperature so as to obtain the second stage lame&r compounds of graphitenitrate. After 2 days, they were taken out from the acid tExchange visitor under the program between JSPS and