X-ray study of phases and structures in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">−</mml:mi></mml:mrow><mml:mrow/><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow/><mml:mrow/><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>He solid solutions

X-ray diffraction has been used to study structural and thermodynamic aspects of isotopic phase separation in solid mixtures of $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$. The phase-separation process has been followed in crystals of 51%, 28%, and 12% $^{3}\mathrm{He}$ and melting pressures between 3.0 and 6.1 MPa. The phase-separation temperatures determined in this work on massive crystals are in general agreement with previous work using other techniques. The pressure dependence of ${T}_{c}$, the highest temperature on the coexistence curve, is found to be linear: ${\mathrm{dT}}_{c}$/dP=-34 mdeg/MPa. The resulting molar volume of mixing is ${v}^{E}$=-0.54x(1-x) ${\mathrm{cm}}^{3}$. Deviation from regular solution behavior, reported in the literature, while possible, is not confirmed. The results of these x-ray measurements also yield detailed structural information which modifies previous understanding of the low-temperature, low-pressure phase diagram of helium isotopic mixtures.

Hali tarjima qilinmagan