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TT: Tiefe Temperaturen

TT 7: Superconductivity & Solids At Low Temperature - Poster Session

TT 7.65: Poster

Montag, 27. März 2006, 14:00–17:45, P1

The Kinetics Asymmetry of the BCC-HCP Phase Transition in Solid Helium-4 — •Yegor Vekhov, Nikolay Mikhin, Andrey Polev, Eduard Rudavskii, and Alexandr Birchenko — B.Verkin Institute for Low Temperature Physics and Engineering, 47 Lenin Ave., Kharkov 61103 , UKRAINE

The subject of research is a solid helium-4. Samples were made by blocking capillary technique. The kinetics of the BCC-HCP structure phase transition was investigated by precise pressure measurement under constant value. The precision of pressure measurement is about 3 mbar and of temperature one is about 5 mK. During step wise temperature changes, within one phase (BCC or HCP), pressure change is described by one-exponential time dependence. During step wise cooling of the sample from the BCC region to the HCP it was found the pressure, at first, is decreasing to the extent of thermal compression of the overcooling BCC phase then, after some delay (5-500 s), the pressure is relaxing once again that is accompanied by a heat generation. The second stage of the pressure relaxation is described by superposition of two exponential dependences with short time constant (1-3 s - directly the BCC-HCP transition) and with long time constant (5-10 s - the relaxation process of defects which were formed during lattice rebuilding). During the inverse HCP-BCC phase transition the delay is practically not observed that can be explained by less BCC nucleation energy [1,2].

[1] T.A.Johnson and C.Elbaum, J. Low Temp.Phys., 107, 317 (1997). [2] Y.Okuda, H.Fujii, Y.Okumura, and H.Mackana, J. Low Temp.Phys., 121, 725 (2000).