Netsu Sokutei, 32 (5), p. 232, (2005)


On the Unusual Thermal Conductivity of Ices at Elevated Pressures

Almost all the numerous forms of ice including 13 crystalline phases, several distinct amorphous states as well as clathrate hydrates have been characterized in terms of their thermal conductivity κ. A few deviations from both the typically strongly decreasing κ(T) (κT-1) associated with crystals and the weakly increasing κ(T) associated with glassy states are observed. In particular, the crystalline clathrate hydrates show glass-like k, whereas low-density amorphous (LDA) ice shows crystal-like κ(κT-0.6). The latter is unique for an amorphous state and indicates that LDA ice exhibits a surprisingly high degree of structural order that allows for high-frequency phonon propagation. It also implies that LDA ice is not the glassy counterpart of ambient liquid water that shows typical amorphous-like behavior. Moreover, the crystalline ices Ih and Ic and LDA ice exhibit abnormal negative pressure coefficients of κ. Both ices Ih and Ic demonstrate pressure-induced amorphization to high-density amorphous (HDA) ice, a state to which also LDA ice transforms on pressurization. The negative pressure coefficient is a signature of phonon softening which leads to a disordering transition upon pressurization.