Crystal structures and thermal expansion of the high pressure phases of ammonium bicarbonate, (ND4)DCO3

In an earlier high-pressure survey of the P,T phase diagram of deuterated ammonium bicarbonate, we observed changes in the neutron powder diffraction patterns that are consistent with a number of polymorphic phase changes. However, data suitable for unambiguous indexing of the powder patterns was not collected and there is a large degree of uncertainty as to whether some of the datasets truly reflect different phases or simply highly anisotropic peaks shifts. Our goal is to cryogenically recover the two high pressure phases (phases II and III) observed at room temperature using the multi-anvil press SAPHiR at the FRM II, Germany, and collect the highest-resolution neutron powder patterns using HRPD, such that we may index new phases with confidence, solve their structures, and observe their behaviour upon warming.