Pressure relaxation and diffusion of vacancies in rapidly grown helium crystals
A.P. Birchenko, 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
Received November 16, 2017
An experimental study of the features of pressure relaxation in rapidly grown crystals of a dilute solution of 3He in 4He was carried out at temperatures above 1.3 K.A cylindrical cell with capacitive pressure sensors at the ends was used for measuring. It was found that at the growth of the helium crystals at the cooling rate higher 4 mK/s, the pressure difference ΔP detected by the sensors at 1.3 K reached 2.4 bar. With a subsequent stepwise increase in temperature, the ΔP value decreased, but disappeared only after careful annealing at the pre-melting temperatures. The kinetics of pres-sure change at the ends of the sample at different temperatures is recorded. The obtained results are interpreted within the framework of the monovacancy model of the diffusion mechanism of structural relaxation. The proposed model made it possible to explain the dependence of ΔP on the time and temperature recorded in the experiment, to find the activation energy of the structural relaxation process and the diffusion coefficient of vacancies. Details of the vacancy model are described in a special appendix.
PACS: 67.80.dj Defects, impurities, and diffusion;
Key words: solid helium, structural relaxation, diffusion, vacancy.
Published online: February 26, 2018