The effect of O2 impurities on the low temperature radial thermal expansion of bundles of closed single-walled carbon nanotubes

The effect of oxygen impurities upon the radial thermal expansion (ar) of bundles of closed single-walled carbon nanotubes has been investigated in the temperature interval 2.2-48 K by the dilatometric method. Saturation of bundles of nanotubes with oxygen caused an increase in the positive ar-values in the whole interval of temperatures used. Also, several peaks appeared in the temperature dependence ar(T) above 20 K. The low temperature desorption of oxygen from powders consisting of bundles of single-walled nanotubes with open and closed ends has been investigatedComment: 7 pages, 3 figure

Quantum effects in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with 4He

The radial thermal expansion (ar) of bundles of single-walled carbon nanotubes saturated with 4He impurities to the molar concentration 9.4% has been investigated in the interval 2.5-9.5 K using the dilatometric method. In the interval 2.1-3.7 K (ar) is negative and is several times higher than the negative (ar) for pure nanotube bundles. This most likely points to 4He atom tunneling between different positions in the nanotube bundle system. The excess expansion was reduced with decreasing 4He concentration.Comment: 4 pages, 1 figure, will be published in Fiz.Nizk Temp. #7, 201

The effect of the noncentral impurity-matrix interaction upon the thermal expansion and polyamorphism of solid CO-C60 solutions at low temperatures

Orientational glasses with CO molecules occupying 26% and 90% of the octahedral interstitial sites in the C60 lattice have been investigated by the dilatometric method in a temperature interval of 2.5 - 23 K. At temperatures 4 - 6 K the glasses undergo a first-order phase transition which is evident from the hysteresis of the thermal expansion and the maxima in the temperature dependences of the linear thermal expansion coefficients, and the thermalization times of the samples. The effect of the noncentral CO-C60 interaction upon the thermal expansion and the phase transition in these glasses was clarified by comparing the behavior of the properties of the CO-C60 and N2-C60 solutions.Comment: 11 pages, 7 figure

Kinetics of 4He gas sorption by fullerite C60. Quantum effects

The kinetics of helium gas sorption by a C60 powder and subsequent desorption of the 4He impurity from the saturated powder has been investigated in the temperature interval T = 2-292 K. Evidence is obtained that supports the existence of two stages in the temperature dependences of sorption and desorption. The stages account for the different times taken by helium to occupy the octahedral and tetrahedral interstices in the C60 lattice. The characteristic times of sorption and desorption coincide. It is found that the temperature dependences of the characteristic times of occupying the octahedral and tetrahedral interstices are nonmonotonic. As the temperature is lowered from 292 K to 79.3 K, the characteristic times increase, which indicates a predominance of thermally activated diffusion of helium in C60. On a further decrease to T = 10 K the characteristic times reduce over an order of magnitude. Below 8 K the characteristic times of sorption and desorption are temperature-independent. This suggests a tunnel character of 4He diffusion in C60.Comment: 6 pages, 2 figure

Radial thermal expansion of single-walled carbon nanotube bundles at low temperatures

The linear coefficient of the radial thermal expansion has been measured on a system of SWNT bundles in an interval of 2.2 - 120K. The measurement was performed using a dilatometer with a sensitivity of 2*10-9 cm. The cylindrical sample 7 mm high and 10 mm in diameter was obtained by compressing powder. The resulting bundles of the nanotubes were oriented perpendicular to the sample axis. The starting powder contained over 90% of SWNTs with the outer diameter 1.1 nm, the length varying within 5-30 um.Comment: 4 pages, 1 figur

The effect of sorbed hydrogen on low temperature radial thermal expansion of single-walled carbon nanotube bundles

The effect of a normal H₂ impurity upon the radial thermal expansion ar of single-walled carbon nanotube (SWNT) bundles has been investigated in the interval T = 2.2–27 K using the dilatometric method. It is found that H₂ saturation of SWNT bundles causes a shift of the temperature interval of the negative thermal expansion towards lower (as compared to pure carbon nanotubes) temperatures and a sharp increase in the magnitude of ar in the whole range of temperatures investigated. The low temperature desorption of H₂ from a powder consisting of bundles of SWNTs, open and closed at the ends, has been investigated