Ice XII in its second regime of metastability
We present neutron powder diffraction results which give unambiguous evidence for the formation of the recently identified new crystalline ice phase [2], labeled ice XII, in completely different conditions. Ice XII is produced here by compressing hexagonal ice I(h) at T = 77, 100, 140, and 160 K up to 1.8 GPa. It can be maintained at ambient pressure in the temperature range 1.5<T<135 K. Accurate structural properties are obtained from high-resolution diffraction carried out at T = 1.5 K. At T = 140 and 160 K additionally ice III/IX is formed. The increasing amount of ice III/IX with increasing temperature gives an upper limit of T approximately 150 K for the successful formation of ice XII with the presented procedure.
Koza
MM
Fachbereich Physik, Universitat Dortmund, D-44221 Dortmund, Germany.
Schober
H
Hansen
T
Tolle
A
Fujara
F