The rare-earth iridates, with general formula A2Ir2O7 (A = rare-earth ion), crystallise in a pyrochlore structure. They display a wide range of exotic magnetic and electronic low temperature properties, dependent on the specific rare-earth ion, due to the inherent magnetic geometric frustration of the rare-earth and Ir4+ (J = ½) corner-sharing tetrahedral lattices. Surprisingly however, initial magnetic ordering of the Ir4+ sublattice appears to be primarily dependent on the A ion size (and hence the interatomic distances/compound’s lattice parameter), rather than the rare-earth’s specific electronic properties. To investigate this relationship, we propose to measure the lattice compressibility and the structural evolution with pressure of several A2Ir2O7 members, to allow proper interpretation of property measurements under pressure. We request beam time to use synchrotron powder X-ray diffraction, in a DAC.