Ice IX
Ice IX is a form of solid water stable at temperatures below 140 K and pressures between 200 and 400 MPa. It has a tetragonal crystal lattice and a density of 1.16 g/cm³, 26% higher than ordinary ice. It is formed by cooling ice III from 208 K to 165 K (rapidly—to avoid forming ice II). Its structure is identical to ice III other than being hydrogen-ordered.

Ordinary water ice is known as ice Ih in the Bridgman nomenclature. Different types of ice, from ice II to ice XVIII, have been created in the laboratory at different temperatures and pressures.
Q283
water
Concept
Q11579
K
Concept
Q44395
MPa
Concept
Q503601
tetragonal
Concept
Q2035889
ice III
DIS
Q3761725
ice II
DIS
Q23392
water ice
Concept
Q1051773
ice Ih
MISC
Q172118
Bridgman
PER
Q3761725
ice II
DIS
Q3375768
ice XVIII
Concept
Q2036633
Ice IX
DIS
+1.16^^http://www.w3.org/2001/XMLSchema#decimal
1.16
NUMBER
+26^^http://www.w3.org/2001/XMLSchema#decimal
26
NUMBER
crystal system
subclass of
subclass of