Ultrasonic-Attenuation and Pressure Measurements in Phase-Separated Solid ³He-⁴He Mixtures

Abstract

The phase separation of solid ³He-⁴He mixtures is known to obey fairly well the regular solution theory, in which the phase separation temperature T_PS is given by

$$ {T_{PS}} = 2{T_c}(1 - 2{X_4})/1n((1 - {X_4})/{X_4}).$$

(1)

Here X₄ is the atomic concentration of ⁴He and T_c = 0.38 K is the critical temperature [1]. MULLIN [2] made a more detailed theory of phase separation based on the self-consistent phonon theory and found an excess volume on mixing ΔV given by

$$ \Delta V = - 0.4{X_4}(1 - {X_4})[c{m^3}/mole].$$

(2)

He predicted a pressure increase on phase separation at a constant volume, which was verified by PANCZYK et al. [3] by using a capacitive strain gauge.