Superionic to superionic phase change in water: consequences for the   interiors of Uranus and Neptune
  Using density functional molecular dynamics free energy calculations, we show that the body-centered-cubic phase of superionic ice previously believed to be the only phase is in fact thermodynamically unstable compared to a novel phase with oxygen positions in fcc lattice sites. The novel phase has a lower proton mobility than the bc phase and may exhibit a higher melting temperature. We predict a transition between the two phases at a pressure of 1 +/- 0.5 Mbar, with potential consequences for the interiors of ice giants such as Uranus and Neptune. 
Hugh F. Wilson, Michael L. Wong, Burkhard Militzer
astro-ph.EP cond-mat.mtrl-sci