  A comprehensive study of the structural properties of the heavily
investigated rare-earth A2Ir2O7 series under extreme conditions is presented.
The series is covered by studying iridates with A = Pr, Sm, Dy-Lu. Temperature-
and pressure-dependent synchrotron X-ray powder diffraction experiments reveal
robustness of the pyrochlore structure throughout the rare-earth series, down
to 4 K and up to 20 GPa. The thermal expansivity and pressure compressibility
are determined, including Debye temperature, bulk modulus and Gr\"uneisen
parameter. Temperature and pressure evolution of the fractional coordinate of
oxygen at 48f Wyckoff position, the sole free atomic position parameter, is
investigated and discussed regarding the antiferromagnetic ordering of the Ir
magnetic moments. In addition, the pressure evolution of the crystal structure
of an IrO2 minority phase is followed. The tetragonal rutile-type structure is
orthorhombically distorted at 15 GPa, and the orthorhombic structure is not
fully stabilised up to 20 GPa.
