Illustrating the experimental method for determining the nucleation time in a bcc-hcp transition (against the background of the P-T diagram for 4He). The dashed curve corresponds to a plot of the maximum attainable supercooling of the bcc phase. 13
Typical time variation of the temperature and pressure during nucleation and the phase transition for two different amounts of supercooling, ΔT, K: 0.08 (a), 0.004 (b). The molar volume Vm = 21.00 ± 0.01 cm3/mole.
Typical temperature dependence of the time delay τ for the bcc-hcp transition. The vertical line on the right indicates the boundary of the region where an equilibrium bcc phase can exist for the given molar volume. The dashed lines are drawn through the experimental data points and the characteristic regions of the τ(T) curve are indicated by the numbers (see text).
Nucleation rate as a function of excess pressure in a supercooled bcc sample. Cell A (●), cell B (∇). The smooth curves J hom and J het are calculated using Eqs. (4) and (5) , respectively (see text).
A comparison of the nucleation rates as a function of supercooling (excess pressure) for annealed (●) and unannealed (▼) samples of crystalline 4He. The smooth curve is drawn through the data for the annealed crystals.
The effect of cyclical supercooling of a bcc sample on the attainable excess pressure ΔP for a molar volume of 21.05 cm3/mole (explanations are given in the text).
Nucleation rate as a function of excess pressure during bcc-hcp transitions in 3He-4He solutions with 1.0% 3He (Vm = 20.98 cm3/mole). The smooth curve is calculated using Eq. (7) and the dashed curve shows data for supercooled annealed samples of the bcc phase of pure 4He with the same molar volume.
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