Helium Phases

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© Recreated from graphics by Low Temperature Laboratory, Helsinki University of Technology.

The phase diagram of 3He is shown in the figure. Note the logarithmic temperature scale. The dot in the lower right hand corner denotes room temperature and pressure. There are two superfluid phases of 3He, A and B. The line within the solid phase indicates a transition between spin-ordered and spin disordered structures (at low and high temperatures, respectively). 4He is the more common isotope of helium. The figure shows the phase diagram of 4He at low temperatures. 4He remains liquid at zero temperature if the pressure is below 2.5 MPa (approximately 25 atmospheres). The liquid has a phase transition to a superfluid phase, also known as He-II, at the temperature of 2.17 K (at vapor pressure). The solid phase has either hexagonal close packed (hcp) or body centered cubic (bcc) symmetry. (Unit: 8)