arXiv subjects

V. A. Konstantinov

Publications and source records attributed to V. A. Konstantinov.

6 recordsLinked to original sources

arXiv2018

Thermal expansion of organic superconductor a-(BEDT-TTF)2 NH4Hg(SCN)4

The temperature dependence of the linear thermal expansion coefficients (LTEC) of a single crystal of a-(BEDT-TTF)2NH4Hg(SCN)4 where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene was studied by the method of precision capacitive dilatometry in the temperature range 2-250 K along the crystallographic direction b* (perpendicular to the crystal layers). Negative values of LTEC were found below 4 K. Probably it is due to charge fluctuations as the temperature approaches the temperature of transition to the superconducting state Tc. It has been suggested that the bends on temperature dependence of LTEC observed in the temperature range 25-45 K are related to order-disorder arrangement of NH4+ ions. Weak maximum of the LTEC, detected at a temperature of about 200-220 K, can be caused by the processes of charge redistribution and the associated intermolecular interaction fluctuations.

cond-mat.supr-con↗

arXiv2017

Thermal expansion of organic superconductor k-(D4-BEDT-TTF)2Cu{N(CN)2}Br. Isotopic effect

Linear thermal expansion coefficient (LTEC) of single crystal k-(D4-BEDT-TTF)2Cu[N(CN)2]Br was studied across the crystal layers in the temperature range 2-290 K using the method of precise capacitive dilatometry. Below Tc = 11,6 K the LTEC of the sample had a small negative value, which is apparently due to the transition from the paramagnetic metal in the superconducting state. There was a bend of temperature dependence of the LTEC, which shows broad peak around 40 K and can be attributed to the elastic lattice anomaly around the end-point of Mott boundary. A sharp jump in the LTEC values and hysteresis was observed in the area of Tg ~ 75-77 K, what is likely explained by the transition in a glass-like state. The isotope effect in the thermal expansion is discusses, which manifested itself in a shift of the phase transitions in comparison with fully deuterated BEDT-TTF sample.

cond-mat.mes-hall↗

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↗

arXiv2003

Influence of rotational motion of molecules on the thermal conductivity of solid SF6, CHCl3, C6H6, and CCl4

The thermal conductivity of solid SF6, CHCI3, C6H6, and CCl4 was investigated by the linear-flow method under saturated vapor pressures in the temperature range from 80 K to the corresponding melting temperatures and then recalculated for a constant density of the samples.The contributions of the phonon -phonon and phonon -rotation interactions to the total thermal resis tance were separated using the modified method of reduced coordinates.It is shown that the phonon- rotation contribution to the thermal resistance of the crystals decreases as the rotational motion of the molecules attains more freedom.

cond-mat.dis-nn↗

arXiv2003

Heat transfer by mobile low-frequency phonons and "localized" modes in cryocrystal solutions

The temperature and volume dependences of the thermal conductivity of solid Kr(1-x)Xe(x)solution are analyzed within the model in which heat is transferred by mobile low-frequency phonons; above the phonon mobility edge this is done by "localized" modes migrating randomly from site to site. The phonon mobility edge (w0)is determined from the condition that the phonon mean -free path restricted by Umklapp processes and point defects scattering cannot be smaller than one-half the phonon wavelength. The Bridgman coefficient is the weighted - mean over these modes whose volume dependences differ widely. It is shown that the amount of heat transferred by the "localized" modes above 100 K is quite large even in pure Kr and it increases with rising temperature and impurity concentration.

cond-mat.mtrl-sci↗