We will investigate the structures of the high temperature (RT to 400K) phases of ammonium iodate, and the features that accompany these phase transitions. From our previous studies we believe that these involve changes in the halogen bond interactions at iodine and the hydrogen bonds between the hydrogen atoms of the ammonium ions and the oxygen atoms of the pseudo perovskite framework. Data collected from our experiment will be used to correlate the changes at the atomic level between the I---O (halogen bonds) N-H---O (hydrogen bonds) and molecular geometry of the iodate and ammonium ions, by a combination of accurate structural refinements and lattice parameter measurements. In addition to the fundamental interest in the properties of hydrogen bonded and halogen bonded systems, we will use the information obtained to rationalise the changes seen in the properties of this material.