This thesis reports the results of neutron diffraction studies and first principles ab initio
simulations of two salt hydrates in the Na2SO4 – H2O and MgSO4 – H2O systems, namely
mirabilite (Na2SO4·10H2O) and meridianiite (MgSO4·11H2O). Neutron diffraction experiments
of deuterated mirabilite were carried on the High Resolution Powder Diffractometer (HPRD)
at the ISIS spallation neutron source to measure its thermal expansion from 4.2 - 300 K and its
incompressibility from 0 – 0.55 GPa. A detailed analysis of both the thermal expansion and
incompressibility data is presented including determination of the thermal expansion tensor
and elastic strain tensor. First principles ab initio calculations were also carried out on both
materials to complement the experimental studies and to extend the study to higher pressures
outside the experimental range. Mirabilite was simulated from 0 – 61 GPa; at least two new
phases were detected resulting from first-order phase transformations. Meridianiite was
simulated from 0 – 11GPa; this material shows one transition to a higher pressure phase
(probably second-order).Finally, a simple model has been developed, incorporating the density
of mirabilite determined in the experiments, to study the size and ascent speed of diapiric salt
hydrate structures as they interact with, and travel through, a more viscous overburden layer
within the upper crust of Earth, Mars and Ganymede, a large icy satellite of Jupiter
