Homogeneous 3He– 4He solid solutions in the pre-separation region

• Published in: Physica. B, Condensed matter Condensed matter, 2011-10, Vol.406 (20), p.3870-3875
• Main Authors: Antsygina, T.N., Lisunov, A.A., Maidanov, V.A., Rubanskyi, V.Y., Rubets, S.P., Rudavskii, E.Ya, Chishko, K.A.
• Format: Article
• Language: English
• Subjects: 3He– 4He solid mixtures; Condensed matter: structure, mechanical and thermal properties; Density fluctuations; Exact sciences and technology; Phase separation; Physics; Quantum fluids and solids; liquid and solid helium; Solid helium and related quantum crystals
• ISSN: 0921-4526; 1873-2135
• DOI: 10.1016/j.physb.2011.07.015

Temperature dependences of the pressure P( T) in homogeneous solid 3He– 4He mixtures have been studied experimentally in the wide range of concentrations (35.0%, 62.0%, 68.3%, 74.1%, 75.0%, and 89.3% 3He) above and below the equilibrium phase separation temperature T s. An anomalous behaviour of the pressure in the vicinity of T s is found for all investigated samples. With decreasing temperature, as T s is approached, the pressure increases instead of expected reduction due to decrease in the phonon contribution ( P ph ∼ T 4 ). Such an increase in pressure continues in the metastable region below T s until the mixture separates. Theoretical interpretation of the observed effects based on a rigorous thermodynamic approach is proposed. The found experimentally pressure behaviour can be described only with the consistent account for fluctuations in the impurity subsystem which near T s dominates over phonon contribution into the pressure. The obtained theoretical results are in good quantitative agreement with the experimental data. Density fluctuations in the concentrated mixtures give rise to a spontaneous formation of impuriton nano-clusters containing several hundreds of atoms. The fluctuation can be rigorously interpreted as a nucleus of the second phase in the pre-separated homogeneous solid mixture. The estimated size of the fluctuation nano-clusters agrees with the corresponding value for second phase nuclei obtained from the Lifshits–Slesov phenomenological theory of homogeneous nucleation.