Structure of recovered ice VII at low temperatures

Water is the most fundamental hydrogen-bonded compound on Earth. We have recently carried out very successful measurements on recovered ice VIII at HRPD which determined for the first time the volume isotope effect in this ice phase (RB1820018). In this follow-up request we wish to compare these results with high-precision volume data of its H-disordered form, ice VII. Some literature data seem to indicate that recovered ice VII is ca. 0.5% less dense than its ordered counter-part, ice VIII. This is totally unexpected since the ice VII-VIII phase boundary has a negative slope over the entire stability range of the two phases. We will investigate this fundamental questions by determining the structure and thermal expansion of D2O VII with high resolution in the range 1.5-120 K. The data will allow us to finalize an important manuscript to be published together with the data of RB1820018.