Visual Observations of Crystal Morphologies and Melting of Ice IV at Pressures up to 1GPa.

Morphologies of ice IV crystals were observed and their melting pressure (P) -temperature (T) relations were determined in a hydrothermal diamond-anvil cell at pressures up to 1 GPa. Water sample and a chip of BaTiO3 were sealed in the sample chamber of the cell, and were observed under a microscope during isochoric cooling-heating cycles. Images of the sample, together with time and T, information, were recorded continuously on VCR tapes. The tetragonal to cubic phase transition in BaTiO3 observed in heating was used to provide pressure and water density information for the sample. Our ice IV melting P-T data are in excellent agreement with those predicted by the equation formulated previously based on the data collected at pressures between 0. 4 and 0. 6 GPa.