The PVT equation of state of D2O ice III / IX

The high-pressure form of solid water, ice III, is the equilibrium phase in contact with liquid water at pressures from about 2.0 - 3.5 kbar. Consequently, its properties are important in calculating the volume changes on freezing of subsurface oceans inside icy planetary bodies and the buoyancy of icy volcanic melts. The incompressibility (bulk modulus) of ice III as found by quantum mechanical simulations is much lower (<60%) than that of the ice phases at neighbouring pressures and temperatures, but the very small stability field of ice III makes its experimental determination difficult. We have a few measurements within its stability field from a recent OSIRIS experiment, and we now intend to combine these with measurements on metastable ice III (= ice IX, when proton ordered) to much higher pressures on PEARL to obtain both the incompressibility and its temperature dependence.

固态水的高压相冰III（ice III）在约2.0~3.5千巴的压力下与液态水处于平衡态。因此，其物性参数对于计算冰质行星体内部地下海洋冻结时的体积变化，以及冰质火山熔体的浮力具有重要意义。通过量子力学模拟得到的冰III的不可压缩性（体积模量，bulk modulus）仅为相近压力与温度下其他冰相的60%以下，远低于后者，但冰III的稳定区间极窄，导致其实验测定难度极大。我们近期通过OSIRIS实验获取了其稳定区间内的少量测量数据，如今计划将这些数据与在PEARL装置上开展的、针对更高压力下亚稳态冰III（质子有序时即为冰IX，ice IX）的测量结果相结合，以同时获取其不可压缩性及其温度依赖性。