Vacancy diffusion and stress relaxation in sup 4 He freezing in porous Vycor

Journal Article · Fri Nov 01 04:00:00 EST 1991 · Physical Review, B: Condensed Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.44.9314· OSTI ID:6380142

Beamish, J R; Mulders, N ^[1]; Hikata, A; Elbaum, C ^[2]

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1. Department of Physics and Astronomy, University of Delaware, Newark, Delaware (USA)
2. Department of Physics, Brown University, Providence, Rhode Island (USA)

We report results of ultrasonic-attenuation and -velocity measurements during freezing of {sup 4}He in porous Vycor glass. When solid helium is present, we observe attenuation peaks whose frequency and temperature dependences are characteristic of a thermally activated relaxation process. We identify the responsible mechanism as being the relaxation of ultrasonic stresses in the solid helium via vacancy diffusion. Since the pores of Vycor are very small ({similar to}10{sup {minus}6} cm), the relaxation time {tau} can be very short. For a sound wave with angular frequency {omega}, the resulting attenuation is largest at the temperature where {omega}{tau}=1. The activation energy for diffusion and the diffusion rates extracted from our measurements are consistent with those determined in other experiments on solid helium. In interpreting other freezing experiments in Vycor, it is important to consider mass transport due to this vacancy-diffusion mechanism, since it can allow pressure equilibrium to be maintained between the helium in the pores and bulk helium outside.

• OSTI ID: 6380142
• Journal Information: Physical Review, B: Condensed Matter; (United States), Journal Name: Physical Review, B: Condensed Matter; (United States) Vol. 44:17; ISSN 0163-1829; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

665420* -- Superfluidity-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACOUSTIC MEASUREMENTS
ACTIVATION ENERGY
ADSORPTION
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DIFFUSION
ENERGY
EVEN-EVEN NUCLEI
FREEZING
FREQUENCY DEPENDENCE
HELIUM 4
HELIUM ISOTOPES
ISOTOPES
LIGHT NUCLEI
MEDIUM PRESSURE
MELTING
NUCLEI
PHASE TRANSFORMATIONS
POINT DEFECTS
POROSITY
PRESSURE DEPENDENCE
RELAXATION
SELF-DIFFUSION
SORPTION
SOUND WAVES
STABLE ISOTOPES
STRESS RELAXATION
TEMPERATURE DEPENDENCE
ULTRALOW TEMPERATURE
ULTRASONIC WAVES
VACANCIES
VAN DER WAALS FORCES
VYCOR