arXiv subjects

V. G. Manzhelii

Publications and source records attributed to V. G. Manzhelii.

At least 19 recordsLinked to original sources

arXiv2014

The low temperature heat capacity of solutions of methane isotopes in fullerite C60. Isotope effects

The heat capacity C(T) of the interstitial solid solution (CH4)0.4C60 has been investigated in the temperature interval 1.4-120 K. The contribution of CH4 molecules to the heat capacity has been separated. The contributions of CH4 and CD4 molecules to the heat capacity of the solutions (CH4)0.40C60 and (CD4)0.40C60 have been compared. It is found that above 80K the character of the rotational motion of CH4 and CD4 molecules changes from libration to hindered rotation. In the interval 14-35 K the heat capacities of CH4 and CD4 molecules are satisfactorily described by contributions of the translational and libration vibrations, as well as the tunnel rotation for the equilibrium distribution of the nuclear spin species. The isotope effect in heat capacity of CH4 and CD4 molecules is due, mainly, the difference in the frequencies of local tranlational and libration vibrations of molecules CH4 and CD4. The contribution of the tunnel rotation of the CH4 and CD4 molecules to the heat capacities of this gases is dominant below 8 K. The isotopic effect is caused by the difference between both the conversion rates and the rotational spectra of the nuclear spin species of CH4 and CD4 molecules. The conversion rate of CH4 molecules is several times lower than that of CD4 ones. Weak features observed in the curves of heat capacity of CH4 and CD4 near 6 K and 8 K, respectively, are most likely a manifestation of first-order phase transitions in the orientational glasses of these solutions.

cond-mat.mes-hall↗

arXiv2013

Sorption of 4He, H2, Ne, N2, CH4 and Kr impurities in graphene oxide at low temperatures. Quantum effects

Sorption and the subsequent desorption of 4He, H2,Ne, N2, CH4 and Kr gas impurities by graphene oxide (GO), glucose-reduced GO (RGO-Gl) and hydrazine-reduced GO (RGO-Hz) powders have been investigated in the temperature interval 2-290 K. It has been found that the sorptive capacity of the reduced sample RGO-Hz is three to six times higher than that of GO. The reduction of GO with glucose has only a slight effect on its sorptive properties. The temperature dependences of the diffusion coefficients of the GO, RGO-Gl and RGO-Hz samples have been obtained using the measured characteristic times of sorption. It is assumed that the temperature dependences of the diffusion coefficients are determined by the competition of the thermally activated and tunneling mechanisms, the tunneling contribution being dominant at low temperatures.

cond-mat.mes-hall↗

arXiv2012

The effect of the glass transition in fullerite C60 on Ar impurity diffusion

The kinetics of sorption and subsequent desorption of argon gas by a C60 powder has been investigated in the temperature interval 58-290 K. The temperature dependence of the coefficients of Ar diffusion in fullerite has been obtained using the measured characteristic times of sorption. The diffusion coefficients of Ar decrease monotonically with lowering temperature in the whole range of the investigated temperatures, which corresponds to the thermally activated diffusion of Ar atoms in fullerite. The glass transition in fullerite induces an order-of-magnitude decrease in the activation energy of Ar diffusion in fullerite. Most likely this is because new directions may appear due to the glass transition in which the barriers separating the interstitial voids in the C60 lattice are significantly lower

cond-mat.mes-hall↗

arXiv2011

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 investigated

cond-mat.mes-hall↗

arXiv2011

Quantum phenomena in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with 3He. A giant isotope effect

The radial thermal expansion αr of bundles of single-walled carbon nanotubes saturated with 3He up to the molar concentration 9.4% has been investigated in the temperature interval 2.1-9.5 K by high-sensitivity capacitance dilatometry. In the interval 2.1-7 K a negative αr was observed, with a magnitude which exceeded the largest negative αr values of pure and 4He-saturated nanotubes by three and two orders of magnitude, respectively. The contributions of the two He isotope impurities to the negative thermal expansion of the nanotube bundles are most likely connected with the spatial redistribution of 4He and 3He atoms by tunneling at the surface and inside nanotube bundles. The isotope effect turned out to be huge, probably owing to the higher tunneling probability of 3He atoms.

cond-mat.mes-hall↗

arXiv2010

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.

cond-mat.mes-hall↗

arXiv2010

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.

cond-mat.mes-hall↗

arXiv2009

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 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 CNTs) 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.

cond-mat.mes-hall↗

arXiv2008

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.

cond-mat.mtrl-sci↗

arXiv2008

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.

cond-mat.dis-nn↗

arXiv2006

Quantitative Evaluation of the Effects of Positional versus Orientational Disorder on the Scattering of Acoustic Phonons in Disordered Matter

The phonon scattering processes on the three solid phases of ethanol are investigated by means of thermal conductivity, light and neutron scattering measurements as well as molecular dynamics simulations on single-crystalline models for the two crystalline modifications (fully ordered monooclinic and orientationally disordered bcc phases). The orientationally disordered crystal is found to exhibit a temperature dependence of the thermal conductivity that is remarkably close to that found for the structurally amorphous solid, specially at low temperatures. The results, together with measurements of the Brillouin linewidths as derived from light scattering measurements emphasize the role of orientational disorder on phonon scattering. The experimental results obtained on polycrystal samples are then discussed with the aid of computer simulations on single-crystalline models of both bcc and monoclinic crystals. Our findings are in good agreement with the wealth of thermodynamic and dynamic data vailable so far [1], but are in stark contrast with inferences made from the analysis of inelastic X-ray data on polycrystalline samples [2], where a common nature for the excitations in all phases is postulated.

cond-mat.dis-nn↗

arXiv2006

Thermal expansion and polyamorphism of N2 - C60 solutions

The linear thermal expansion coefficients a(T) of N2 - C60 solutions with 9.9% and 100% of the C60 lattice interstitials filled with N2 have been investigated in the interval 2.2 - 24 K. The dependence a(T) has a hysteresis suggesting co-existence of two types of orientational glasses in these solutions. The features of the glasses are compared. The characteristic times of phase transformations in the solutions and reorientation of C60 molecules have been estimated.

cond-mat.mtrl-sci↗

arXiv2004

Thermal Conductivity of Methane-Hydrate

The thermal conductivity of the methane hydrate CH4 (5.75 H2O) was measured in the interval 2-140 K using the steady-state technique. The thermal conductivity corresponding to a homogeneous substance was calculated from the measured effective thermal conductivity obtained in the experiment. The temperature dependence of the thermal conductivity is typical for the thermal conductivity of amorphous solids. It is shown that after separation of the hydrate into ice and methane, at 240 K, the thermal conductivity of the ice exhibits a dependence typical of heavily deformed fine-grain polycrystal. The reason for the glass-like behavior in the thermal conductivity of clathrate compounds has been discussed. The experimental results can be interpreted within the phenomenological soft-potential model with two fitting parameters.

cond-mat.dis-nn↗

arXiv2004

Low temperature anomaly of heat capacity of CD4 rotors in solid CD4-Kr solution

The heat capacity of the solid Kr-CD4 (13% CD4) solution has been investigated. It is shown that the temperature dependence of the heat capacity Crot of the rotational subsystem in this solution is radically different from the corresponding dependences in the previously studied Kr-CD4 (1%, 5% CD4) and Kr-CH4 (5-60%) solutions. A model is proposed to explain the observed dependence Crot(T). The experimental results can be described taking into account the contribution to the heat capacity from CD4 molecules that are in weak, medium and strong molecular fields. The mean concentrations and energy differences between the ground and first excited energy levels of the CD4 molecules in these molecular fields have been estimated.

cond-mat.other↗

arXiv2004

Heat transfer in gama-phase of oxygen

The isochoric thermal conductivity of gama-O2 has been studied on samples of varying density in the temperature interval from 44 K to the onset of melting. The thermal conductivity of nearly free sample decreases at rising temperature along the isochores. It is shown that the absolute value of thermal conductivity in the gama-phase of O2 is close to its lower limit and most of the heat is transported by "diffusive" modes. The growth of thermal conductivity in gama-O2 is attributed to the decay of the phonon scattering at the rotational excitations of the molecules and at the short-range magnetic order fluctuations at rising temperature.

cond-mat.dis-nn↗

arXiv2004

Isochoric thermal conductivity of solid nitrogen

The isochoric thermal conductivity of solid nitrogen has been investigated on four samples of different densities in the temperature interval from 20 K to the onset of melting. In alfa-N2 the isochoric thermal conductivity exhibits a dependence weaker than 1/T; in beta-N2 it increases slightly with temperature. The experimental results are discussed within a model in which the heat is transported by low-frequency phonons or by "diffusive" modes above the mobility boundary. The growth of the thermal conductivity in beta-N2 is attributed to the decreasing "rotational" component of the total thermal resistance, which occurs as the rotational correlations between the neighboring molecules become weaker.

cond-mat.dis-nn↗

arXiv2004

On the polyamorphism of fullerite-based orientational glasses

The dilatometric investigation in the temperature range of 2-28K shows that a first-order polyamorphous transition occurs in the orientational glasses based on C60 doped with H2, D2 and Xe. A polyamorphous transition was also detected in C60 doped with Kr and He. It is observed that the hysteresis of thermal expansion caused by the polyamorphous transition (and, hence, the transition temperature) is essentially dependent on the type of doping gas. Both positive and negative contributions to the thermal expansion were observed in the low temperature phase of the glasses. The relaxation time of the negative contribution occurs to be much longer than that of the positive contribution. The positive contribution is found to be due to phonon and libron modes, whilst the negative contribution is attributed to tunneling states of the C60 molecules. The characteristic time of the phase transformation from the low-T phase to the high-T phase has been found for the C60-H2 system at 12K. A theoretical model is proposed to interpret these observed phenomena. The theoretical model proposed, includes a consideration of the nature of polyamorphism in glasses, as well as the thermodynamics and kinetics of the transition. A model of non-interacting tunneling states is used to explain the negative contribution to the thermal expansion. The experimental data obtained is considered within the framework of the theoretical model. From the theoretical model the order of magnitude of the polyamorphous transition temperature has been estimated. It is found that the late stage of the polyamorphous transformation is described well by the Kolmogorov law with an exponent of n=1. At this stage of the transformation, the two-dimensional phase boundary moves along the normal, and the nucleation is not important.

cond-mat.dis-nn↗

arXiv2003

Quantum Effects in Thermal Conductivity of Solid Krypton - Methane Solutions

The dynamic interaction of a quantum rotor with its crystalline environment has been studied by measurement of the thermal conductivity of solid Kr1_c(CH4)_c solutions at c = 0.05-0.75 in the temperature region from 2 up to 40K. The thermal resistance of the solutions was mainly determined by the resonance scattering of phonons by CH4 molecules with the nuclear spin I=1 (the nuclear spin of T-species). The influence of the nuclear spin conversion on the temperature dependence of the thermal conductivity k(T) was found: a clearly defined minimum on k(T), its temperature position depending on the CH4 concentration. It was shown that the anisotropy molecular field not increase monotonously with the CH4 concentration. A compensation effect in the mutual orientation arrangement of the neighboring rotors is observed at c > 0.5. The temperature dependence of Kr1_c(CH4)_c is described within the Debye model of thermal conductivity taking into account the lower limit of the phonon mean free path. The anomalous temperature dependence of the thermal resistance shows the evolution of the phonon-rotation coupling at varying temperature. It increases strongly when the character of CH4 rotation changes from the quantum at low temperatures to classical at high temperatures. Also, a jump of thermal conductivity (a sharp increase in k(T) within a narrow temperature range) was observed, whose position varies from 9.7 K to 8.4 K when the CH4 concentration changes from 0.25 to 0.45.

cond-mat.mtrl-sci↗