Specific heat of a one-dimensional carbon phase synthesized by condensation of high-temperature carbon gas

We report on the specific heat, $C(T)$, measurements in the temperature ranges 4.5 K $<T<$ 30 K and 130 K $<T<$ 730 K of a one-dimensional carbon crystal phase synthesized by condensation of high-temperature carbon gas. Even at the lowest achieved temperatures, the measured $C(T)$ dependence, to the first approximation, is close to the linear dependence over the wide temperature range from 15 K to 30 K. For the adequate description of the measured low-temperature $C(T)$ dependence, the chainlike crystal structure of the material has been considered, and the model of specific heat for quasi-one-dimensional crystals has been applied. By means of x-ray and high-temperature specific-heat measurements it has been found that the material is a metastable phase under the normal conditions, undergoing complicated irreversible transformations to the amorphous state upon heating above $T\ensuremath{\approx}350$ K.