Fizika Nizkikh Temperatur: Volume 44, Number 9 (September 2018), p. 1196-1204    ( to contents , go back )

New features of pressure relaxation in nonequilibrium helium crystals

A.P. Bisrchenko, N.P. Mikhin, E.Ya. Rudavskii, S.N. Smirnov, and Ya.Yu. Fysun

B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
E-mail: mikhin@ilt.kharkov.ua

Received May 15, 2018, published online July 26, 2018

Abstract

The method of precision barometry has been used to study the processes of structural relaxation in nonequilibrium helium crystals obtained by liquid crystallization during rapid cooling in the temperature range 1.3–1.7 K. In the course of the experiment, the pressure at the ends of a cylindrical measuring cell with solid helium and their variation with time during a stepwise heating of the sample was measured. The experimental results on the kinetics of relaxation are analyzed in the paper, when the pressure values recorded by both sensors increased with time. Analysis of the experimental results gives estimates of the average atomic concentration of vacancies in the crystal, the values of the vacancy diffusion coefficient, and the activation energy of vacancy motion. The work continues the study of structural pressure relaxation started in the article published earlier (Low Temp. Phys. 44, 304 (2018)), where a model describing the relaxation of internal stresses in nonequilibrium helium crystals due to the diffusion current of vacancies was proposed to interpret the experimental data.

Key words: solid helium, structural relaxation, diffusion, vacancy.

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