This proposal seeks PEARL and HRPD beam time to study the pressure and temperature dependence of the crystal structures of deuterated caesium, ammonium and thallium bifluoride. The PEARL experiment will investigate the behaviour of all three bifluoride salts at room temperature for pressures up to 9 GPa. In so doing, we will be able to further contrast and compare the phase transition behaviour of the monovalent bifluorides and azides, which have also been studied recently on PEARL. The HRPD experiment will consist of an investigation at ambient pressure of the full crystal structure of thallium bifluoride over the temperature interval 10-320 K. The main aims here will be to obtain the first complete structure solution of this system and investigate the temperature dependence of the intriguing ...Tl...F-H-F...Tl... chain motif reported in the original early X-ray structure solution.