LATTICE-CONSTANTS AND THERMAL-EXPANSION OF H2O AND D2O ICE IH BETWEEN10 AND 265 K

The lattice constants of powdered H2O and D2O ice Ih were measured in the temperature range 10-265 K with synchrotron radiation to a precisi on of typically 0.003% in a and 0.007% in c. The c/a ratio remains alm ost constant with temperature, thus the thermal expansion is virtually isotropic. Below 73 K, one observes a negative thermal expansion for both light and heavy ice Ih. The temperature dependency of the thermal expansion at higher temperatures follows roughly that of the specific heat. Thus, the Gruneisen function is negative at low temperatures an d is slowly varying above 120 K; the isotopic differences of the Grune isen function are smaller than previously assumed.