Kinetics of the bcc–hcp transition in He4 off the melting curve

• Published in: Low temperature physics (Woodbury, N.Y.) N.Y.), 2006-12, Vol.32 (12), p.1118-1122
• Main Authors: Birchenko, A. P., Vekhov, Ye. O., Mikhin, N. P., Polev, A. V., Rudavskii, E. Ya
• Format: Article
• Language: English
• ISSN: 1063-777X; 1090-6517
• DOI: 10.1063/1.2400684

The kinetics of the bcc–hcp structural phase transition in He4 is investigated by the method of precision barometry in the pressure range 25–31 bar and temperature range 1.25–1.90K. Under constant-volume conditions the kinetics of the pressure and temperature variations is recorded in the range of molar volumes Vm=20.85–21.10cm3∕mole. It is found that the process of cooling is accompanied by an unusual two-stage relaxation of the pressure: initially an exponential decrease of the pressure occurs due to thermal contraction of the supercooled bcc phase, and then the structural transition itself occurs very rapidly. The latter is accompanied by a pronounced thermal effect due to the release of the heat of the phase transition. It is shown that the inverse, hcp–bcc phase transition occurs in one stage (without a delay) and is accompanied by absorption of the heat of transition. Experimental data on the variation of the pressure are obtained in the bcc and hcp single-phase regions and along the bcc–hcp phase equilibrium line.